                                       
                                       
                       Technical Support Document (TSD)
                         for the final Transport Rule
                      Docket ID No. EPA-HQ-OAR-2009-0491
                                       
                                       
                                       
                                       
                                       
                                       
                            Power Sector Variability
                                Final Rule TSD

                                       
                                       

                     U.S. Environmental Protection Agency
                          Office of Air and Radiation
                                   June 2011
                           Power Sector Variability
      
      This Technical Support Document (TSD) provides information in support of section VI.E, "Approach to Power Sector Emissions Variability," of the preamble to the final Transport Rule.  This TSD is organized as follows:
      
      1. Introduction
      2. Estimating variability in power system operations and emissions
      3. Numerical simulation of 1 and 3-year variability
      4. Results of an analysis using the air quality assessment tool
      
      1. Introduction.
      Section VI of the preamble to the final Transport Rule discusses EPA's approach to define "significant contribution" and "interference with maintenance" with respect to the 1997 8-hour ozone and annual fine particle (PM2.5) National Ambient Air Quality Standards (NAAQS) and the 2006 24-hour PM2.5 NAAQS.  As discussed in preamble section VI, EPA has identified the emissions that must be reduced by each state to address the state's significant contribution and interference with maintenance.  To facilitate implementation of the requirement that these emissions be eliminated, EPA also developed SO2, annual NOX, and ozone-season NOX state budgets based on its projections of state-by-state power sector emissions in an average year reflecting these emission reductions. 
      However, because of inherent variability in year-to-year baseline emissions  -  resulting from the inherent variability in power system operations  -  state-level emissions may vary somewhat from year to year even after all the significant contribution and interference with maintenance that EPA has identified in the Transport Rule has been eliminated.  Therefore, and for the reasons discussed in preamble sections VI.E and VI.F, EPA has determined that it is appropriate to develop variability limits for each state budget.  These limits are used to identify the range of emissions that EPA believes may occur in each state following the elimination of all emissions identified by EPA as significantly contributing to nonattainment or interfering with maintenance in one or more other states.  
      Preamble sections VI.A through VI.D discuss EPA's approach to quantify for each upwind state the emissions that significantly contribute to nonattainment or interfere with maintenance downwind for the existing ozone and PM2.5 NAAQS and to determine state emissions budgets for SO2, annual NOX, and ozone season NOX.  Preamble sections VI.E and VI.F discuss the inherent variability in electric power system operations and EPA's approach to determine appropriate variability limits on emissions for each state covered by the final Transport Rule to account for this variability.  As explained in preamble section VI.E, EPA calculated variability limits for each state emissions budget.  The final Transport Rule applies those variability limits in addition to the state budgets (which are based on expected average conditions) to determine the "assurance level" for each state in each compliance period.  The Agency believes that because baseline power system operations (and therefore emissions) are variable at the state level, emissions after the elimination of all significant contribution and interference with maintenance are also variable and thus it is appropriate to take this variability into account while assuring that each state makes necessary reductions.  
      In the final Transport Rule, EPA derived "1-year" variability limits from an assessment of historical year-to-year variability in heat input, which was originally described in the "Power Sector Variability" TSD from the proposed Transport Rule and is re-analyzed in this TSD for all states included in the final Transport Rule, as well as for the additional states EPA is proposing, through a supplemental proposal, to include in the Transport Rule ozone program.  For the reasons discussed in section VI.E of the preamble, although EPA proposed to implement both 1-year variability limits and 3-year average variability limits, the final Transport Rule decided to finalize only the 1-year limits.  Section 3 of this TSD presents an analysis of 1 and 3-year variability that supports EPA's decision to finalize only the 1-year variability limits in the final rule.
      Section 4 of this TSD describes an analysis using the air quality assessment tool (AQAT) to estimate the resulting air quality effects in a given year assuming several potential degrees of variability in year-to-year emissions from the power sector.  
      
      2. Estimating variability in power system operations and emissions.    
      This section describes the method that the Agency used to estimate the year-to-year ("1-year") variability in power system operations and thereby annual SO2, annual NOX and ozone season NOX emissions.  As discussed above, the goal of this assessment is to determine the amount of variability in state-level emissions that is due to inherent variability in power system operations.  To quantify this expected variability, EPA used variation in historic heat input.  EPA considered the use of variation in historic emissions but determined this to be inappropriate because it reflected factors such as the installation of new emissions controls and changes in the operation of existing controls.  These factors are not directly related to variability in power system operations.  In fact, these factors are activities that EPA is attempting to regulate with the implementation of the state budgets themselves.  EPA believes that all controls  (existing or newly installed) should be operated with consistency under the rule's programs.  As such, EPA is assuming a constant relationship between heat input variability and emissions variability for the purposes of this historic variability analysis (i.e., variation in heat input is a proxy for variation in emissions holding the effectiveness of emissions control in that state constant).  This section in the TSD provides information on:
   * The historical data set EPA established on a state-by-state basis of yearly heat input values applicable to each of the pollutants regulated in the final Transport Rule (SO2, annual NOx, and ozone season NOx).  EPA used these historical heat input values to estimate the inherent variability in emissions due to power system operation.
   * The method EPA utilized to estimate the year-to-year variability in the heat input values.  The year-to-year variability in heat input was estimated on a state-by-state basis.
   * The approach EPA used to link inherent heat input variability with projected pollutant emission levels to estimate the resulting variation expected in future pollutant emissions on a year-to-year basis.


   (a) Establishing a historical data set for use in estimating inherent variability in emissions.
       The objective of this section is to describe the inherent year-to-year (1-year) variability in emissions by characterizing the year-to-year variance in total annual heat input for each state in the Transport Rule.  EPA is concerned with variation in total emissions from year to year (or the variation in total emissions from one ozone season to the next), as compliance with the Transport Rule programs must be demonstrated for total tonnage emitted during a single year or ozone season.  For this assessment, EPA used total yearly heat input values equaling the sum of heat input from all units operating in each state during a particular year.
      EPA estimated the expected variation in power sector emissions for a yearly time period based on the "standard deviation" of yearly power sector heat input (HI) assessed over a 7-year time frame (2002 through 2008).  EPA believes such data would capture inherent variation in year-to-year emissions due to factors such as variation in power demand, timing of maintenance activities, and unexpected shutdown of units.  These factors are strongly correlated with heat input and variation in electric generation. 
      EPA chose the time period 2002 through 2008 for the analysis of variation in heat input because it features nearly comprehensive reporting of heat input across many states and EGUs while also minimizing unusual (i.e., statistically misleading for long-run averaging) upswings or downswings in state-level heat input.  EPA selected 2002 as the first baseline year because prior years (2000 and 2001) experienced large, uneven changes in annual heat input from fossil units for some states due, in part, to structural changes in the composition of the power sector fleet and a significant increase in newly reported heat input due to the commencement of the second phase of the Acid Rain Program (ARP).  Consequently, incorporating data from years prior to 2002 in the analysis would lead to the inclusion of a year where there is large change in heat input that is not representative of typical year-to-year variability in power system operation, thereby leading to overestimates of variability.  EPA determined that including years marked by significant changes in the number of units reporting heat input data or years experiencing significant shifts in state-level EGU fleet composition (i.e., sharp regional swings from coal to gas generation) would skew the variability estimates.  EPA maintained 2008 as the final year for the assessment for a similar reason:  The economic downturn in 2009 resulted in an atypical dropoff in electric demand and, thus, in heat input, that would overstate long-run year-to-year variability in heat input.  
      For each year of the 7-year time period, EPA estimated total power sector heat input on a state-by-state basis using the sum of reported heat input for all units within each of three general classes of EGUs:  (1) coal-fired units; (2) combined cycle turbines; and (3) a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.  Total annual heat input values (in million MMBtu) for the coal-fired EGUs and for all EGUs can be found in Table 1 and Table 2, respectively.  Ozone-season heat input values for all EGUs can be found in Table 3.  EPA assessed the inherent year-to-year variability in annual and ozone season NOx emissions using the total yearly heat inputs summed across all EGUs (Tables 2 and 3, respectively), because heat input from each of these sources is related to significant NOx emissions.  The Agency assessed year-to-year variability in annual SO2 emissions using the yearly heat inputs from the coal-fired EGUs (Table 1) which account for a substantial majority of the SO2 emissions.  SO2 emission rates are considerably higher at most coal-fired units compared to other types of generators; as a result, heat input variation at coal-fired units has a disproportionate impact on a state's SO2 emissions.  For this reason, in this assessment, we analyzed historic variability in heat input at coal-fired units as a better proxy for SO2 emissions variability.
      EGUs built prior to 2002 that reported heat input and emissions data between 2002 and 2008 and new EGUs built in 2002 or later were included for this analysis.  EGUs that were built prior to 2002 but that did not start reporting until after 2002 were excluded from the assessment, in order to prevent their newly reported heat input from falsely registering as "additional" heat input gained in that state in that year. 
Table 1: Annual Heat Input* (million MMBtu) from Coal-Fired Units for Each Year.
                                     State
                                                                           2002
                                                                           2003
                                                                           2004
                                                                           2005
                                                                           2006
                                                                           2007
                                                                           2008
                                                                     Average HI
                                      AL
                                                                          779.0
                                                                          822.6
                                                                          784.5
                                                                          828.3
                                                                          813.0
                                                                          818.8
                                                                          768.9
                                                                          802.1
                                      GA
                                                                          781.2
                                                                          787.4
                                                                          808.8
                                                                          871.6
                                                                          872.5
                                                                          910.6
                                                                          861.1
                                                                          841.9
                                      IA
                                                                          393.1
                                                                          389.6
                                                                          386.7
                                                                          384.5
                                                                          378.9
                                                                          415.9
                                                                          431.2
                                                                          397.1
                                      IL
                                                                          930.9
                                                                          961.9
                                                                        1,027.1
                                                                        1,002.1
                                                                        1,002.1
                                                                        1,030.5
                                                                        1,032.9
                                                                          998.2
                                      IN
                                                                        1,231.4
                                                                        1,236.3
                                                                        1,266.0
                                                                        1,281.2
                                                                        1,269.9
                                                                        1,256.9
                                                                        1,243.6
                                                                        1,255.0
                                      KS
                                                                          427.5
                                                                          427.5
                                                                          411.9
                                                                          405.2
                                                                          377.6
                                                                          405.4
                                                                          373.5
                                                                          404.1
                                      KY
                                                                          946.5
                                                                          931.1
                                                                          938.1
                                                                          970.3
                                                                          987.0
                                                                          977.9
                                                                          978.5
                                                                          961.3
                                      MD
                                                                          276.9
                                                                          278.0
                                                                          269.9
                                                                          273.7
                                                                          274.7
                                                                          277.1
                                                                          256.0
                                                                          272.3
                                      MI
                                                                          700.1
                                                                          706.9
                                                                          709.7
                                                                          721.1
                                                                          699.7
                                                                          736.0
                                                                          714.4
                                                                          712.5
                                      MN
                                                                          389.2
                                                                          411.0
                                                                          386.7
                                                                          380.1
                                                                          370.3
                                                                          362.9
                                                                          349.8
                                                                          378.6
                                      MO
                                                                          724.5
                                                                          769.6
                                                                          770.8
                                                                          783.6
                                                                          783.5
                                                                          762.0
                                                                          732.8
                                                                          761.0
                                      NC
                                                                          693.3
                                                                          689.1
                                                                          696.5
                                                                          719.7
                                                                          699.1
                                                                          726.4
                                                                          713.2
                                                                          705.3
                                      NE
                                                                          227.0
                                                                          238.3
                                                                          231.2
                                                                          238.3
                                                                          234.0
                                                                          222.4
                                                                          233.8
                                                                          232.1
                                      NJ
                                                                           80.0
                                                                           75.3
                                                                           79.6
                                                                           92.2
                                                                           81.9
                                                                           77.8
                                                                           62.8
                                                                           78.5
                                      NY
                                                                          234.1
                                                                          235.9
                                                                          226.7
                                                                          213.4
                                                                          211.2
                                                                          211.0
                                                                          181.0
                                                                          216.2
                                      OH
                                                                        1,290.2
                                                                        1,316.3
                                                                        1,247.3
                                                                        1,315.1
                                                                        1,294.0
                                                                        1,319.7
                                                                        1,290.0
                                                                        1,296.1
                                      PA
                                                                        1,026.9
                                                                        1,050.1
                                                                        1,078.6
                                                                        1,090.2
                                                                        1,090.5
                                                                        1,105.2
                                                                        1,065.1
                                                                        1,072.4
                                      SC
                                                                          381.5
                                                                          384.7
                                                                          401.4
                                                                          407.7
                                                                          410.4
                                                                          422.6
                                                                          417.1
                                                                          403.7
                                      TN
                                                                          624.7
                                                                          574.9
                                                                          589.4
                                                                          586.3
                                                                          606.9
                                                                          617.2
                                                                          578.0
                                                                          596.8
                                      TX
                                                                        1,529.9
                                                                        1,572.9
                                                                        1,580.3
                                                                        1,581.3
                                                                        1,546.5
                                                                        1,590.7
                                                                        1,565.7
                                                                        1,566.7
                                      VA
                                                                          340.5
                                                                          312.5
                                                                          296.7
                                                                          298.4
                                                                          288.0
                                                                          298.9
                                                                          264.2
                                                                          299.9
                                      WI
                                                                          457.1
                                                                          475.9
                                                                          482.9
                                                                          473.2
                                                                          451.2
                                                                          447.5
                                                                          450.8
                                                                          462.6
                                      WV
                                                                          898.8
                                                                          898.5
                                                                          851.0
                                                                          861.2
                                                                          852.4
                                                                          883.3
                                                                          851.6
                                                                          871.0
*Source:  EPA, March 2010. All relevant ARP units in the Transport Rule region.  These data are available at http://www.epa.gov/airmarkets/ through Data and Maps.Table 2: Total Annual Heat Input* (million MMBtu) from All Three** EGU Categories for Units Greater Than or Equal to 25 MW for Each Year.
                                     State
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
                                  Average HI
                                      AL
                                                                          901.0
                                                                          916.0
                                                                          904.6
                                                                          936.6
                                                                          964.1
                                                                        1,000.0
                                                                          938.9
                                                                          937.3
                                      GA
                                                                          841.9
                                                                          822.4
                                                                          853.4
                                                                          948.0
                                                                          968.5
                                                                        1,033.0
                                                                          958.2
                                                                          917.9
                                      IA
                                                                          393.2
                                                                          390.3
                                                                          391.2
                                                                          401.3
                                                                          396.3
                                                                          438.0
                                                                          446.5
                                                                          408.1
                                      IL
                                                                          976.1
                                                                          982.7
                                                                        1,046.2
                                                                        1,053.8
                                                                        1,038.2
                                                                        1,086.2
                                                                        1,059.9
                                                                        1,034.7
                                      IN
                                                                        1,256.8
                                                                        1,257.5
                                                                        1,283.6
                                                                        1,315.1
                                                                        1,300.4
                                                                        1,301.2
                                                                        1,282.2
                                                                        1,285.3
                                      KS
                                                                          429.2
                                                                          429.4
                                                                          412.5
                                                                          406.8
                                                                          381.2
                                                                          410.0
                                                                          378.6
                                                                          406.8
                                      KY
                                                                          962.4
                                                                          935.1
                                                                          942.4
                                                                          988.3
                                                                          999.0
                                                                          997.2
                                                                          987.8
                                                                          973.2
                                      MD
                                                                          288.2
                                                                          290.6
                                                                          280.8
                                                                          287.8
                                                                          282.6
                                                                          286.0
                                                                          263.7
                                                                          282.8
                                      MI
                                                                          726.9
                                                                          725.1
                                                                          727.3
                                                                          760.5
                                                                          730.7
                                                                          776.5
                                                                          743.8
                                                                          741.5
                                      MN
                                                                          399.0
                                                                          423.1
                                                                          396.4
                                                                          401.8
                                                                          391.7
                                                                          394.6
                                                                          371.6
                                                                          396.9
                                      MO
                                                                          752.1
                                                                          788.7
                                                                          792.2
                                                                          813.6
                                                                          812.5
                                                                          800.6
                                                                          770.3
                                                                          790.0
                                      NC
                                                                          718.8
                                                                          706.3
                                                                          718.4
                                                                          747.2
                                                                          727.1
                                                                          767.7
                                                                          749.7
                                                                          733.6
                                      NE
                                                                          228.4
                                                                          240.5
                                                                          233.5
                                                                          245.3
                                                                          240.7
                                                                          231.9
                                                                          240.3
                                                                          237.2
                                      NJ
                                                                          139.3
                                                                          132.9
                                                                          151.5
                                                                          154.9
                                                                          158.8
                                                                          172.7
                                                                          172.8
                                                                          154.7
                                      NY
                                                                          288.3
                                                                          297.3
                                                                          309.9
                                                                          322.9
                                                                          380.6
                                                                          393.1
                                                                          366.6
                                                                          337.0
                                      OH
                                                                        1,309.6
                                                                        1,330.3
                                                                        1,258.3
                                                                        1,340.0
                                                                        1,313.6
                                                                        1,354.5
                                                                        1,310.4
                                                                        1,316.7
                                      PA
                                                                        1,060.2
                                                                        1,090.0
                                                                        1,155.1
                                                                        1,172.4
                                                                        1,185.4
                                                                        1,240.9
                                                                        1,200.0
                                                                        1,157.7
                                      SC
                                                                          418.2
                                                                          402.7
                                                                          442.1
                                                                          454.9
                                                                          461.5
                                                                          474.0
                                                                          464.4
                                                                          445.4
                                      TN
                                                                          635.7
                                                                          580.5
                                                                          592.1
                                                                          592.6
                                                                          613.2
                                                                          623.8
                                                                          582.3
                                                                          602.9
                                      TX
                                                                        2,247.3
                                                                        2,378.4
                                                                        2,540.8
                                                                        2,650.2
                                                                        2,658.4
                                                                        2,752.9
                                                                        2,698.6
                                                                        2,561.0
                                      VA
                                                                          356.6
                                                                          333.6
                                                                          329.5
                                                                          339.5
                                                                          324.0
                                                                          354.8
                                                                          312.3
                                                                          335.7
                                      WI
                                                                          475.3
                                                                          494.1
                                                                          498.4
                                                                          528.5
                                                                          492.3
                                                                          497.4
                                                                          490.0
                                                                          496.6
                                      WV
                                                                          900.5
                                                                          899.9
                                                                          852.0
                                                                          863.3
                                                                          855.8
                                                                          887.1
                                                                          853.3
                                                                          873.1
*Source:  EPA, March 2010. All relevant ARP units in the Transport Rule region.  These data are available at http://www.epa.gov/airmarkets/ through Data and Maps.
** Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.
                                       
                                       
                                       
                                       
Table 3: Total Annual Heat Input* (million MMBtu) from All Three** EGU Categories for Units Greater Than or Equal to 25 MW for Ozone Season.

                                     State
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
                                  Average HI
                                      AL
                                                                          427.4
                                                                          428.8
                                                                          423.6
                                                                          427.2
                                                                          456.9
                                                                          469.9
                                                                          432.5
                                                                          438.1
                                      AR
                                                                          124.0
                                                                          152.5
                                                                          149.2
                                                                          142.0
                                                                          173.6
                                                                          170.4
                                                                          150.5
                                                                          151.7
                                      FL
                                                                          548.6
                                                                          554.9
                                                                          563.3
                                                                          615.1
                                                                          639.0
                                                                          656.3
                                                                          646.0
                                                                          603.3
                                      GA
                                                                          403.8
                                                                          382.9
                                                                          407.1
                                                                          461.8
                                                                          469.5
                                                                          489.6
                                                                          449.9
                                                                          437.8
                                      IA
                                                                          170.8
                                                                          161.8
                                                                          161.8
                                                                          183.5
                                                                          168.9
                                                                          189.8
                                                                          182.0
                                                                          174.1
                                      IL
                                                                          454.9
                                                                          430.2
                                                                          449.6
                                                                          478.0
                                                                          460.8
                                                                          474.6
                                                                          452.6
                                                                          457.2
                                      IN
                                                                          557.2
                                                                          545.4
                                                                          540.7
                                                                          578.4
                                                                          566.4
                                                                          559.8
                                                                          550.5
                                                                          556.9
                                      KS
                                                                          183.2
                                                                          180.9
                                                                          176.8
                                                                          180.6
                                                                          172.2
                                                                          177.1
                                                                          160.7
                                                                          175.9
                                      KY
                                                                          433.3
                                                                          400.1
                                                                          401.0
                                                                          434.4
                                                                          435.3
                                                                          436.1
                                                                          417.8
                                                                          422.6
                                      LA
                                                                           94.7
                                                                          121.7
                                                                          144.9
                                                                          149.9
                                                                          161.8
                                                                          150.7
                                                                          152.2
                                                                          139.4
                                      MD
                                                                          134.8
                                                                          118.8
                                                                          121.8
                                                                          131.5
                                                                          123.3
                                                                          126.8
                                                                          117.1
                                                                          124.9
                                      MI
                                                                          331.0
                                                                          312.1
                                                                          304.6
                                                                          339.9
                                                                          328.5
                                                                          344.5
                                                                          321.1
                                                                          326.0
                                      MO
                                                                          337.7
                                                                          347.6
                                                                          348.0
                                                                          354.2
                                                                          362.8
                                                                          357.7
                                                                          341.7
                                                                          349.9
                                      MS
                                                                          117.8
                                                                          116.2
                                                                          129.5
                                                                          137.3
                                                                          147.7
                                                                          155.9
                                                                          143.2
                                                                          135.4
                                      NC
                                                                          332.9
                                                                          308.5
                                                                          314.0
                                                                          341.5
                                                                          340.4
                                                                          351.5
                                                                          344.8
                                                                          333.4
                                      NJ
                                                                           68.7
                                                                           59.9
                                                                           73.9
                                                                           76.1
                                                                           79.9
                                                                           86.1
                                                                           86.6
                                                                           75.9
                                      NY
                                                                          126.1
                                                                          121.4
                                                                          136.3
                                                                          152.5
                                                                          174.7
                                                                          170.5
                                                                          158.9
                                                                          148.6
                                      OH
                                                                          583.7
                                                                          562.8
                                                                          538.4
                                                                          574.4
                                                                          562.0
                                                                          596.7
                                                                          553.3
                                                                          567.3
                                      OK
                                                                          204.5
                                                                          223.4
                                                                          220.0
                                                                          248.4
                                                                          244.6
                                                                          241.1
                                                                          247.9
                                                                          232.8
                                      PA
                                                                          465.4
                                                                          468.7
                                                                          494.6
                                                                          529.3
                                                                          530.6
                                                                          550.8
                                                                          515.5
                                                                          507.8
                                      SC
                                                                          203.1
                                                                          178.4
                                                                          204.8
                                                                          214.1
                                                                          215.8
                                                                          222.7
                                                                          222.0
                                                                          208.7
                                      TN
                                                                          291.2
                                                                          244.3
                                                                          256.2
                                                                          270.1
                                                                          273.2
                                                                          278.9
                                                                          261.2
                                                                          267.9
                                      TX
                                                                        1,031.9
                                                                        1,089.9
                                                                        1,170.0
                                                                        1,229.1
                                                                        1,255.4
                                                                        1,262.8
                                                                        1,252.7
                                                                        1,184.6
                                      VA
                                                                          160.0
                                                                          146.9
                                                                          150.9
                                                                          154.3
                                                                          151.5
                                                                          167.9
                                                                          144.5
                                                                          153.7
                                      WI
                                                                          218.5
                                                                          211.1
                                                                          207.4
                                                                          240.0
                                                                          223.0
                                                                          219.8
                                                                          208.5
                                                                          218.3
                                      WV
                                                                          379.5
                                                                          384.5
                                                                          361.0
                                                                          375.4
                                                                          373.1
                                                                          390.3
                                                                          366.9
                                                                          375.8
*Source:  EPA, March 2010; All relevant ARP units in the Transport Rule region.  These data are available at http://www.epa.gov/airmarkets/ through Data and Maps.
** Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.

                                       

      (b) Estimating the state-by-state variability in heat input using historical heat input data sets.
      This subsection describes the method EPA used to estimate the variability in heat input for each state covered by the final Transport Rule.  It repeats some of the relevant data and calculations presented in the proposed Transport Rule TSD "Power Sector Variability" with updates reflecting the states covered by the final Transport Rule.  
      In the final Transport Rule, EPA used the method presented in the proposed Transport Rule and assessed the year-to-year variability over the 7-year time period of the yearly total heat input values or ozone season heat input values by deriving a standard deviation for each state while "screening out" overall growth or decline in heat input over that time period.  This method is described in detail in this and the following subsections and was selected for two reasons: First, it held constant any longer trend in growth or decline in a state's heat input over the baseline period analyzed.  Second, a statistical approach (i.e., using the standard deviation) is less sensitive to data anomalies present in finite data sets; in other words, it effectively screens out extraneous information to characterize long-run variability.   
      For each state, it was important to first adjust the data set to screen out trends (growth or decline) in heat input over the 7-year time period, so that the data would then reflect year-to-year variability independent of trends in electricity demand.  After controlling for growth in heat input over time, the year-to-year variation in heat input was assessed, as the differences between the actual yearly heat input values and the "yearly" average heat input values estimated according to the trend.  To account for trends, a simple least-squares linear regression equation was fit to the heat input data as a function of time.  In other words, this step of the analysis attempts to define the amount of variability in the data set for each state that can be attributed to a trend over time, which EPA is attempting to hold constant in this analysis to determine year-to-year variability independent of longer-run trends in heat input (e.g., rising electricity demand).
      This process fits a straight line to the data points using an equation of the form (y = mx+b).  In this equation, "y" is the estimated heat input (million MMBtu) for a particular year "x", m is the slope of the line (with units of million MMBtu/year), and b is the "y-intercept" (the heat input value when the line is extrapolated to x = 0).  The value of r[2], the square of the Pearson product moment correlation coefficient, describes the proportion of variance in "y" that is accounted for by knowing "x".  It indicates how significant a trend (growth or decline) is present in the data.  Large r[2] values (r[2] values are maximized at 1) indicate that the least squares fit picks up a strong trend (upward or downward) in the data which should be removed by the procedure described below.  This is important for states where there was substantial growth or decline in heat input over the time period (i.e., for states that have slopes for the regression line that are substantially different than zero).  Small r[2] values, on the other hand, indicate that the least squares fit did not detect a strong trend (upward or downward) in the heat input data.  Consequently, the procedure described below has less of a corrective role to play, since there is no strong trend that needs to be controlled for (held constant) when characterizing the data set's year-to-year variability.  
      For each state, the slopes of the regression equations, y-intercepts, and r[2] values can be found in Tables 4, 5, and 6.  Using the slope and y-intercept from the regression equation for each state, yearly heat input values were estimated for each state for each year between 2002 and 2008 (Tables 4, 5, and 6).  Year-to-year variation was assessed for each year or for each ozone season as the difference between the actual heat input (from Tables 1-3) and the heat input estimated using the regression equation (Tables 4-6).
      
      
Table 4: Heat Input (million MMBtu) from Coal-Fired Units for Each Year Estimated Using the Regression Equation.

                                     State
                Slope of Linear Regression (million MMBtu/year)
                                   Intercept
                                  r[2] Value
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
                                      AL
                                                                          -0.34
                                                                          1,492
                                                                           0.00
                                                                          803.2
                                                                          802.8
                                                                          802.5
                                                                          802.1
                                                                          801.8
                                                                          801.5
                                                                          801.1
                                      GA
                                                                          19.64
                                                                        -38,527
                                                                           0.74
                                                                          783.0
                                                                          802.6
                                                                          822.3
                                                                          841.9
                                                                          861.5
                                                                          881.2
                                                                          900.8
                                      IA
                                                                           5.69
                                                                        -11,002
                                                                           0.41
                                                                          380.1
                                                                          385.8
                                                                          391.4
                                                                          397.1
                                                                          402.8
                                                                          408.5
                                                                          414.2
                                      IL
                                                                          14.94
                                                                        -28,960
                                                                           0.70
                                                                          953.4
                                                                          968.3
                                                                          983.3
                                                                          998.2
                                                                        1,013.2
                                                                        1,028.1
                                                                        1,043.0
                                      IN
                                                                           2.92
                                                                         -4,592
                                                                           0.12
                                                                        1,246.3
                                                                        1,249.2
                                                                        1,252.1
                                                                        1,255.0
                                                                        1,257.9
                                                                        1,260.9
                                                                        1,263.8
                                      KS
                                                                          -8.59
                                                                         17,633
                                                                           0.74
                                                                          429.9
                                                                          421.3
                                                                          412.7
                                                                          404.1
                                                                          395.5
                                                                          386.9
                                                                          378.3
                                      KY
                                                                           8.52
                                                                        -16,113
                                                                           0.68
                                                                          935.8
                                                                          944.3
                                                                          952.8
                                                                          961.3
                                                                          969.9
                                                                          978.4
                                                                          986.9
                                      MD
                                                                          -2.13
                                                                          4,545
                                                                           0.36
                                                                          278.7
                                                                          276.6
                                                                          274.5
                                                                          272.3
                                                                          270.2
                                                                          268.1
                                                                          265.9
                                      MI
                                                                           3.26
                                                                         -5,825
                                                                           0.30
                                                                          702.8
                                                                          706.0
                                                                          709.3
                                                                          712.5
                                                                          715.8
                                                                          719.1
                                                                          722.3
                                      MN
                                                                          -8.25
                                                                         16,915
                                                                           0.80
                                                                          403.3
                                                                          395.1
                                                                          386.8
                                                                          378.6
                                                                          370.3
                                                                          362.1
                                                                          353.8
                                      MO
                                                                           0.80
                                                                           -836
                                                                           0.01
                                                                          758.6
                                                                          759.4
                                                                          760.2
                                                                          761.0
                                                                          761.8
                                                                          762.6
                                                                          763.4
                                      NC
                                                                           4.90
                                                                         -9,111
                                                                           0.54
                                                                          690.6
                                                                          695.5
                                                                          700.4
                                                                          705.3
                                                                          710.2
                                                                          715.1
                                                                          720.0
                                      NE
                                                                          -0.32
                                                                            869
                                                                           0.01
                                                                          233.1
                                                                          232.8
                                                                          232.5
                                                                          232.1
                                                                          231.8
                                                                          231.5
                                                                          231.2
                                      NJ
                                                                          -1.58
                                                                          3,241
                                                                           0.15
                                                                           83.2
                                                                           81.7
                                                                           80.1
                                                                           78.5
                                                                           76.9
                                                                           75.4
                                                                           73.8
                                      NY
                                                                          -8.01
                                                                         16,282
                                                                           0.85
                                                                          240.2
                                                                          232.2
                                                                          224.2
                                                                          216.2
                                                                          208.2
                                                                          200.2
                                                                          192.2
                                      OH
                                                                           1.88
                                                                         -2,480
                                                                           0.03
                                                                        1,290.4
                                                                        1,292.3
                                                                        1,294.2
                                                                        1,296.1
                                                                        1,298.0
                                                                        1,299.8
                                                                        1,301.7
                                      PA
                                                                           8.46
                                                                        -15,880
                                                                           0.46
                                                                        1,047.0
                                                                        1,055.5
                                                                        1,063.9
                                                                        1,072.4
                                                                        1,080.8
                                                                        1,089.3
                                                                        1,097.7
                                      SC
                                                                           6.84
                                                                        -13,312
                                                                           0.90
                                                                          383.1
                                                                          390.0
                                                                          396.8
                                                                          403.7
                                                                          410.5
                                                                          417.3
                                                                          424.2
                                      TN
                                                                          -1.36
                                                                          3,314
                                                                           0.02
                                                                          600.8
                                                                          599.5
                                                                          598.1
                                                                          596.8
                                                                          595.4
                                                                          594.1
                                                                          592.7
                                      TX
                                                                           3.89
                                                                         -6,231
                                                                           0.15
                                                                        1,555.1
                                                                        1,559.0
                                                                        1,562.9
                                                                        1,566.7
                                                                        1,570.6
                                                                        1,574.5
                                                                        1,578.4
                                      VA
                                                                          -9.45
                                                                         19,252
                                                                           0.77
                                                                          328.2
                                                                          318.8
                                                                          309.3
                                                                          299.9
                                                                          290.4
                                                                          281.0
                                                                          271.5
                                      WI
                                                                          -3.84
                                                                          8,161
                                                                           0.34
                                                                          474.2
                                                                          470.3
                                                                          466.5
                                                                          462.6
                                                                          458.8
                                                                          455.0
                                                                          451.1
                                      WV
                                                                          -6.09
                                                                         13,082
                                                                           0.36
                                                                          889.2
                                                                          883.2
                                                                          877.1
                                                                          871.0
                                                                          864.9
                                                                          858.8
                                                                          852.7

                                       
Table 5: Total Heat Input (million MMBtu) from All Three* EGU Categories for Each Year Estimated Using the Regression Equation.

                                     State
                Slope of Linear Regression (million MMBtu/year)
                                   Intercept
                                  r[2] Value
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
                                      AL
                                                                          12.18
                                                                        -23,490
                                                                           0.55
                                                                          900.8
                                                                          913.0
                                                                          925.1
                                                                          937.3
                                                                          949.5
                                                                          961.7
                                                                          973.9
                                      GA
                                                                          31.61
                                                                        -62,466
                                                                           0.75
                                                                          823.1
                                                                          854.7
                                                                          886.3
                                                                          917.9
                                                                          949.5
                                                                          981.1
                                                                        1,012.8
                                      IA
                                                                           9.30
                                                                        -18,233
                                                                           0.72
                                                                          380.2
                                                                          389.5
                                                                          398.8
                                                                          408.1
                                                                          417.4
                                                                          426.7
                                                                          436.0
                                      IL
                                                                          16.09
                                                                        -31,231
                                                                           0.73
                                                                          986.5
                                                                        1,002.5
                                                                        1,018.6
                                                                        1,034.7
                                                                        1,050.8
                                                                        1,066.9
                                                                        1,083.0
                                      IN
                                                                           6.44
                                                                        -11,635
                                                                           0.39
                                                                        1,265.9
                                                                        1,272.4
                                                                        1,278.8
                                                                        1,285.3
                                                                        1,291.7
                                                                        1,298.2
                                                                        1,304.6
                                      KS
                                                                          -7.92
                                                                         16,295
                                                                           0.70
                                                                          430.6
                                                                          422.7
                                                                          414.8
                                                                          406.8
                                                                          398.9
                                                                          391.0
                                                                          383.1
                                      KY
                                                                           9.17
                                                                        -17,418
                                                                           0.56
                                                                          945.7
                                                                          954.8
                                                                          964.0
                                                                          973.2
                                                                          982.3
                                                                          991.5
                                                                        1,000.7
                                      MD
                                                                          -2.89
                                                                          6,080
                                                                           0.47
                                                                          291.5
                                                                          288.6
                                                                          285.7
                                                                          282.8
                                                                          279.9
                                                                          277.0
                                                                          274.1
                                      MI
                                                                           5.60
                                                                        -10,480
                                                                           0.37
                                                                          724.7
                                                                          730.3
                                                                          735.9
                                                                          741.5
                                                                          747.1
                                                                          752.7
                                                                          758.3
                                      MN
                                                                          -5.14
                                                                         10,702
                                                                           0.53
                                                                          412.3
                                                                          407.2
                                                                          402.0
                                                                          396.9
                                                                          391.7
                                                                          386.6
                                                                          381.5
                                      MO
                                                                           3.53
                                                                         -6,280
                                                                           0.12
                                                                          779.4
                                                                          782.9
                                                                          786.5
                                                                          790.0
                                                                          793.5
                                                                          797.0
                                                                          800.6
                                      NC
                                                                           8.00
                                                                        -15,302
                                                                           0.63
                                                                          709.6
                                                                          717.6
                                                                          725.6
                                                                          733.6
                                                                          741.6
                                                                          749.6
                                                                          757.6
                                      NE
                                                                           0.92
                                                                         -1,612
                                                                           0.11
                                                                          234.4
                                                                          235.4
                                                                          236.3
                                                                          237.2
                                                                          238.1
                                                                          239.1
                                                                          240.0
                                      NJ
                                                                           6.69
                                                                        -13,250
                                                                           0.90
                                                                          134.6
                                                                          141.3
                                                                          148.0
                                                                          154.7
                                                                          161.4
                                                                          168.1
                                                                          174.8
                                      NY
                                                                          17.76
                                                                        -35,264
                                                                           0.82
                                                                          283.7
                                                                          301.4
                                                                          319.2
                                                                          337.0
                                                                          354.7
                                                                          372.5
                                                                          390.2
                                      OH
                                                                           3.79
                                                                         -6,281
                                                                           0.07
                                                                        1,305.3
                                                                        1,309.1
                                                                        1,312.9
                                                                        1,316.7
                                                                        1,320.5
                                                                        1,324.3
                                                                        1,328.1
                                      PA
                                                                          26.84
                                                                        -52,648
                                                                           0.85
                                                                        1,077.2
                                                                        1,104.0
                                                                        1,130.9
                                                                        1,157.7
                                                                        1,184.5
                                                                        1,211.4
                                                                        1,238.2
                                      SC
                                                                          10.75
                                                                        -21,104
                                                                           0.79
                                                                          413.2
                                                                          423.9
                                                                          434.6
                                                                          445.4
                                                                          456.1
                                                                          466.9
                                                                          477.6
                                      TN
                                                                          -1.88
                                                                          4,376
                                                                           0.04
                                                                          608.5
                                                                          606.6
                                                                          604.8
                                                                          602.9
                                                                          601.0
                                                                          599.1
                                                                          597.2
                                      TX
                                                                          79.30
                                                                       -156,429
                                                                           0.86
                                                                        2,323.1
                                                                        2,402.4
                                                                        2,481.7
                                                                        2,561.0
                                                                        2,640.3
                                                                        2,719.6
                                                                        2,798.8
                                      VA
                                                                          -3.42
                                                                          7,203
                                                                           0.21
                                                                          346.0
                                                                          342.6
                                                                          339.2
                                                                          335.7
                                                                          332.3
                                                                          328.9
                                                                          325.5
                                      WI
                                                                           1.60
                                                                         -2,711
                                                                           0.05
                                                                          491.8
                                                                          493.4
                                                                          495.0
                                                                          496.6
                                                                          498.2
                                                                          499.8
                                                                          501.4
                                      WV
                                                                          -5.83
                                                                         12,568
                                                                           0.33
                                                                          890.6
                                                                          884.8
                                                                          879.0
                                                                          873.1
                                                                          867.3
                                                                          861.5
                                                                          855.6
                                       
* Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.
Table 6: Heat Input (million MMBtu) from All Three* EGU Categories for Ozone Season Estimated Using the Regression Equation.

                                     State
                Slope of Linear Regression (million MMBtu/year)
                                   Intercept
                                  r[2] Value
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
                                      AL
                                                                           4.68
                                                                         -8,936
                                                                           0.32
                                                                          424.0
                                                                          428.7
                                                                          433.4
                                                                          438.1
                                                                          442.7
                                                                          447.4
                                                                          452.1
                                      AR
                                                                           4.99
                                                                         -9,850
                                                                           0.41
                                                                          136.8
                                                                          141.8
                                                                          146.8
                                                                          151.7
                                                                          156.7
                                                                          161.7
                                                                          166.7
                                      FL
                                                                          20.38
                                                                        -40,256
                                                                           0.90
                                                                          542.2
                                                                          562.5
                                                                          582.9
                                                                          603.3
                                                                          623.7
                                                                          644.1
                                                                          664.4
                                      GA
                                                                          14.80
                                                                        -29,231
                                                                           0.64
                                                                          393.4
                                                                          408.2
                                                                          423.0
                                                                          437.8
                                                                          452.6
                                                                          467.4
                                                                          482.2
                                      IA
                                                                           3.44
                                                                         -6,732
                                                                           0.45
                                                                          163.7
                                                                          167.2
                                                                          170.6
                                                                          174.1
                                                                          177.5
                                                                          181.0
                                                                          184.4
                                      IL
                                                                           3.33
                                                                         -6,214
                                                                           0.20
                                                                          447.3
                                                                          450.6
                                                                          453.9
                                                                          457.2
                                                                          460.6
                                                                          463.9
                                                                          467.2
                                      IN
                                                                           1.23
                                                                         -1,911
                                                                           0.04
                                                                          553.2
                                                                          554.4
                                                                          555.7
                                                                          556.9
                                                                          558.1
                                                                          559.4
                                                                          560.6
                                      KS
                                                                          -2.84
                                                                          5,880
                                                                           0.65
                                                                          184.5
                                                                          181.6
                                                                          178.8
                                                                          175.9
                                                                          173.1
                                                                          170.3
                                                                          167.4
                                      KY
                                                                           2.15
                                                                         -3,883
                                                                           0.08
                                                                          416.1
                                                                          418.3
                                                                          420.4
                                                                          422.6
                                                                          424.7
                                                                          426.9
                                                                          429.0
                                      LA
                                                                           8.84
                                                                        -17,590
                                                                           0.67
                                                                          112.9
                                                                          121.7
                                                                          130.6
                                                                          139.4
                                                                          148.3
                                                                          157.1
                                                                          166.0
                                      MD
                                                                          -1.27
                                                                          2,671
                                                                           0.18
                                                                          128.7
                                                                          127.4
                                                                          126.1
                                                                          124.9
                                                                          123.6
                                                                          122.3
                                                                          121.1
                                      MI
                                                                           2.10
                                                                         -3,891
                                                                           0.10
                                                                          319.7
                                                                          321.8
                                                                          323.9
                                                                          326.0
                                                                          328.1
                                                                          330.2
                                                                          332.3
                                      MO
                                                                           1.68
                                                                         -3,026
                                                                           0.17
                                                                          344.9
                                                                          346.6
                                                                          348.3
                                                                          349.9
                                                                          351.6
                                                                          353.3
                                                                          355.0
                                      MS
                                                                           6.21
                                                                        -12,325
                                                                           0.80
                                                                          116.7
                                                                          122.9
                                                                          129.1
                                                                          135.4
                                                                          141.6
                                                                          147.8
                                                                          154.0
                                      NC
                                                                           5.29
                                                                        -10,265
                                                                           0.50
                                                                          317.5
                                                                          322.8
                                                                          328.1
                                                                          333.4
                                                                          338.7
                                                                          343.9
                                                                          349.2
                                      NJ
                                                                           4.01
                                                                         -7,956
                                                                           0.82
                                                                           63.9
                                                                           67.9
                                                                           71.9
                                                                           75.9
                                                                           79.9
                                                                           83.9
                                                                           87.9
                                      NY
                                                                           8.39
                                                                        -16,679
                                                                           0.74
                                                                          123.4
                                                                          131.8
                                                                          140.2
                                                                          148.6
                                                                          157.0
                                                                          165.4
                                                                          173.8
                                      OH
                                                                           0.01
                                                                            552
                                                                           0.00
                                                                          567.3
                                                                          567.3
                                                                          567.3
                                                                          567.3
                                                                          567.3
                                                                          567.3
                                                                          567.3
                                      OK
                                                                           6.80
                                                                        -13,402
                                                                           0.75
                                                                          212.4
                                                                          219.2
                                                                          226.0
                                                                          232.8
                                                                          239.6
                                                                          246.4
                                                                          253.2
                                      PA
                                                                          12.52
                                                                        -24,588
                                                                           0.69
                                                                          470.3
                                                                          482.8
                                                                          495.3
                                                                          507.8
                                                                          520.4
                                                                          532.9
                                                                          545.4
                                      SC
                                                                           5.58
                                                                        -10,974
                                                                           0.62
                                                                          192.0
                                                                          197.5
                                                                          203.1
                                                                          208.7
                                                                          214.3
                                                                          219.8
                                                                          225.4
                                      TN
                                                                          -0.12
                                                                            517
                                                                           0.00
                                                                          268.2
                                                                          268.1
                                                                          268.0
                                                                          267.9
                                                                          267.7
                                                                          267.6
                                                                          267.5
                                      TX
                                                                          39.05
                                                                        -77,113
                                                                           0.85
                                                                        1,067.4
                                                                        1,106.5
                                                                        1,145.5
                                                                        1,184.6
                                                                        1,223.6
                                                                        1,262.7
                                                                        1,301.7
                                      VA
                                                                          -0.14
                                                                            434
                                                                           0.00
                                                                          154.1
                                                                          154.0
                                                                          153.9
                                                                          153.7
                                                                          153.6
                                                                          153.4
                                                                          153.3
                                      WI
                                                                           0.10
                                                                             24
                                                                           0.00
                                                                          218.0
                                                                          218.1
                                                                          218.2
                                                                          218.3
                                                                          218.4
                                                                          218.5
                                                                          218.6
                                      WV
                                                                          -0.50
                                                                          1,387
                                                                           0.01
                                                                          377.3
                                                                          376.8
                                                                          376.3
                                                                          375.8
                                                                          375.3
                                                                          374.8
                                                                          374.3
      
* Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.
      
      
      On a state-by-state basis, EPA calculated the difference between the actual heat input and the estimated heat input using the regression equation for each year (2002 through 2008).  The differences for SO2, annual NOx, and ozone season NOx can be found in Tables 7, 8, and 9, respectively.  Some of these yearly differences are positive, while others are negative; the size of the variation on either side of the regression line is meaningful for this analysis.  EPA assessed the differences between actual and estimated heat input across all years for each state and pollutant by calculating the standard deviation.  
      The standard deviation is defined as the square root of the variance (the sum of the square of the differences divided by the number of samples minus one).  The state- and pollutant-specific representative differences (defined using the standard deviation) were used for the remaining steps in the variability analyses.  In using the standard deviation as a representative difference, we assume that:  (1) differences between the actual and modeled heat inputs are "normally" distributed; and that (2) yearly mean values are independent. 
      For each state, the standard deviation of the differences is a conventional statistical measure of the year-to-year (1-year) variation in heat input.  The statistical definition of a standard deviation in this context conveys that, on average, 68% of all the year-specific heat input values over the long run would be no farther from the average annual heat input (either higher or lower) than by the amount measured as the standard deviation.  
       The standard deviation can also be used to estimate, on average, the probability of larger variations in heat input (for example a difference that we would expect less than 1% of the time).  Using the standard deviation, "confidence levels" representing the variability difference in heat input that could be expected at different probabilities were found for each state for each pollutant.  Following the analysis from the proposed Transport Rule and after reviewing all relevant public comment, the two-tailed 95[th] percent confidence level was selected as the appropriate level of variation.  The two-tailed 95[th] percent confidence level indicates that we could expect that, on average, the total heat input for a particular year for a particular state will be within 1.960 standard deviations of the variation from its mean value 95 percent of the time.  This statistical confidence interval is very commonly used to make future projections from data sets similar to EPA's purpose in this analysis.  As described in the proposal, EPA believes that using the 95[th] percent confidence level provides a high degree of confidence that sources subject to the rule will be able to operate within the constraints of the variability limits while still meeting their obligations to provide a reliable electricity supply across the states affected.  
      The 95% upper confidence level heat inputs and fractions (the 95% heat input difference divided by the average heat input over the 2002-2008 time period) can be found in Tables 7, 8, and 9.  
      The standard deviation in the heat input in million MMBtu rounded to three significant digits can be found in Tables 7, 8, and 9.  The standard deviation of the heat input was divided by the average heat input value, resulting in a fraction (when the fraction is multiplied by one hundred, the result is the standard deviation percent variation).
Table 7: Difference between Heat Input (million MMBtu) Measured and Estimated for Coal-Fired Units for Each Year Using the Regression Equation.

                                     State
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
               Standard Deviation of Heat Input (million MMBtu)
                 Average Heat Input (2002-2008 (from Table 1)
                Standard Deviation as a Fraction of Average HI
            95% Confidence Level Variability in HI (million MMBtu)
       95% Confidence Level Variability in HI (as a Fraction of Avg. HI)
                                      AL
                                                                          -24.1
                                                                           19.7
                                                                          -18.0
                                                                           26.1
                                                                           11.2
                                                                           17.3
                                                                          -32.2
                                                                           24.0
                                                                          802.1
                                                                           0.03
                                                                           47.0
                                                                          0.059
                                      GA
                                                                           -1.8
                                                                          -15.2
                                                                          -13.5
                                                                           29.7
                                                                           11.0
                                                                           29.4
                                                                          -39.7
                                                                           25.4
                                                                          841.9
                                                                           0.03
                                                                           49.7
                                                                          0.059
                                      IA
                                                                           13.0
                                                                            3.9
                                                                           -4.8
                                                                          -12.7
                                                                          -23.9
                                                                            7.4
                                                                           17.0
                                                                           14.6
                                                                          397.1
                                                                          0.037
                                                                           28.7
                                                                          0.073
                                      IL
                                                                          -22.5
                                                                           -6.4
                                                                           43.8
                                                                            3.8
                                                                          -11.0
                                                                            2.4
                                                                          -10.1
                                                                           21.3
                                                                          998.2
                                                                          0.021
                                                                           41.7
                                                                          0.041
                                      IN
                                                                          -14.9
                                                                          -12.9
                                                                           13.9
                                                                           26.1
                                                                           11.9
                                                                           -4.0
                                                                          -20.2
                                                                           17.5
                                                                        1,255.0
                                                                          0.014
                                                                           34.3
                                                                          0.027
                                      KS
                                                                           -2.4
                                                                            6.3
                                                                           -0.8
                                                                            1.1
                                                                          -17.9
                                                                           18.4
                                                                           -4.8
                                                                           11.0
                                                                          404.1
                                                                          0.027
                                                                           21.6
                                                                          0.053
                                      KY
                                                                           10.7
                                                                          -13.2
                                                                          -14.8
                                                                            9.0
                                                                           17.2
                                                                           -0.5
                                                                           -8.4
                                                                           12.6
                                                                          961.3
                                                                          0.013
                                                                           24.7
                                                                          0.025
                                      MD
                                                                           -1.8
                                                                            1.4
                                                                           -4.6
                                                                            1.4
                                                                            4.5
                                                                            9.0
                                                                          -10.0
                                                                            6.2
                                                                          272.3
                                                                          0.023
                                                                           12.1
                                                                          0.045
                                      MI
                                                                           -2.7
                                                                            0.8
                                                                            0.5
                                                                            8.5
                                                                          -16.1
                                                                           16.9
                                                                           -7.9
                                                                           10.7
                                                                          712.5
                                                                          0.015
                                                                           21.0
                                                                          0.029
                                      MN
                                                                          -14.1
                                                                           16.0
                                                                           -0.2
                                                                            1.6
                                                                            0.0
                                                                            0.8
                                                                           -4.0
                                                                            8.9
                                                                          378.6
                                                                          0.023
                                                                           17.4
                                                                          0.045
                                      MO
                                                                          -34.0
                                                                           10.2
                                                                           10.7
                                                                           22.6
                                                                           21.7
                                                                           -0.6
                                                                          -30.6
                                                                           23.4
                                                                          761.0
                                                                          0.031
                                                                           45.9
                                                                          0.061
                                      NC
                                                                            2.7
                                                                           -6.5
                                                                           -4.0
                                                                           14.3
                                                                          -11.1
                                                                           11.3
                                                                           -6.8
                                                                            9.7
                                                                          705.3
                                                                          0.014
                                                                           19.1
                                                                          0.027
                                      NE
                                                                           -6.1
                                                                            5.6
                                                                           -1.3
                                                                            6.2
                                                                            2.2
                                                                           -9.1
                                                                            2.6
                                                                            5.8
                                                                          232.1
                                                                          0.025
                                                                           11.4
                                                                          0.049
                                      NJ
                                                                           -3.3
                                                                           -6.4
                                                                           -0.5
                                                                           13.7
                                                                            5.0
                                                                            2.4
                                                                          -11.0
                                                                            8.1
                                                                           78.5
                                                                          0.103
                                                                           15.8
                                                                          0.202
                                      NY
                                                                           -6.2
                                                                            3.7
                                                                            2.5
                                                                           -2.8
                                                                            3.1
                                                                           10.8
                                                                          -11.1
                                                                            7.3
                                                                          216.2
                                                                          0.034
                                                                           14.2
                                                                          0.067
                                      OH
                                                                           -0.2
                                                                           24.0
                                                                          -46.9
                                                                           19.0
                                                                           -4.0
                                                                           19.8
                                                                          -11.8
                                                                           24.8
                                                                        1,296.1
                                                                          0.019
                                                                           48.5
                                                                          0.037
                                      PA
                                                                          -20.1
                                                                           -5.4
                                                                           14.7
                                                                           17.8
                                                                            9.7
                                                                           15.9
                                                                          -32.7
                                                                           19.9
                                                                        1,072.4
                                                                          0.019
                                                                           39.1
                                                                          0.037
                                      SC
                                                                           -1.6
                                                                           -5.3
                                                                            4.6
                                                                            4.1
                                                                           -0.1
                                                                            5.3
                                                                           -7.1
                                                                            4.9
                                                                          403.7
                                                                          0.012
                                                                            9.7
                                                                          0.024
                                      TN
                                                                           23.8
                                                                          -24.6
                                                                           -8.7
                                                                          -10.4
                                                                           11.5
                                                                           23.1
                                                                          -14.7
                                                                           19.3
                                                                          596.8
                                                                          0.032
                                                                           37.8
                                                                          0.063
                                      TX
                                                                          -25.2
                                                                           14.0
                                                                           17.5
                                                                           14.5
                                                                          -24.2
                                                                           16.1
                                                                          -12.8
                                                                           19.8
                                                                        1,566.7
                                                                          0.013
                                                                           38.8
                                                                          0.025
                                      VA
                                                                           12.3
                                                                           -6.3
                                                                          -12.7
                                                                           -1.5
                                                                           -2.4
                                                                           17.9
                                                                           -7.3
                                                                           11.1
                                                                          299.9
                                                                          0.037
                                                                           21.7
                                                                          0.073
                                      WI
                                                                          -17.1
                                                                            5.6
                                                                           16.4
                                                                           10.5
                                                                           -7.7
                                                                           -7.5
                                                                           -0.3
                                                                           11.7
                                                                          462.6
                                                                          0.025
                                                                           22.9
                                                                          0.049
                                      WV
                                                                            9.5
                                                                           15.4
                                                                          -26.1
                                                                           -9.7
                                                                          -12.5
                                                                           24.5
                                                                           -1.1
                                                                           17.6
                                                                          871.0
                                                                           0.02
                                                                           34.5
                                                                          0.039

Table 8: Difference between Total Heat Input (million MMBtu) Measured and Estimated from All Three* EGU Categories for Each Year Using the Regression Equation.

                                     State
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
               Standard Deviation of Heat Input (million MMBtu)
                 Average Heat Input (2002-2008 (from Table 2)
                Standard Deviation as a Fraction of Average HI
            95% Confidence Level Variability in HI (million MMBtu)
       95% Confidence Level Variability in HI (as a Fraction of Avg. HI)
                                      AL
                                                                            0.2
                                                                            3.0
                                                                          -20.5
                                                                           -0.7
                                                                           14.6
                                                                           38.3
                                                                          -35.0
                                                                           23.6
                                                                          937.3
                                                                          0.025
                                                                           46.2
                                                                          0.049
                                      GA
                                                                           18.8
                                                                          -32.3
                                                                          -32.9
                                                                           30.1
                                                                           18.9
                                                                           51.8
                                                                          -54.5
                                                                           39.6
                                                                          917.9
                                                                          0.043
                                                                           77.6
                                                                          0.084
                                      IA
                                                                           13.0
                                                                            0.8
                                                                           -7.7
                                                                           -6.8
                                                                          -21.2
                                                                           11.3
                                                                           10.5
                                                                           12.6
                                                                          408.1
                                                                          0.031
                                                                           24.8
                                                                          0.061
                                      IL
                                                                          -10.4
                                                                          -19.8
                                                                           27.5
                                                                           19.1
                                                                          -12.6
                                                                           19.3
                                                                          -23.1
                                                                           21.2
                                                                        1,034.7
                                                                          0.020
                                                                           41.5
                                                                          0.039
                                      IN
                                                                           -9.2
                                                                          -14.8
                                                                            4.8
                                                                           29.8
                                                                            8.7
                                                                            3.0
                                                                          -22.3
                                                                           17.3
                                                                        1,285.3
                                                                          0.013
                                                                           33.9
                                                                          0.025
                                      KS
                                                                           -1.4
                                                                            6.7
                                                                           -2.3
                                                                           -0.1
                                                                          -17.7
                                                                           19.1
                                                                           -4.4
                                                                           11.2
                                                                          406.8
                                                                          0.027
                                                                           21.9
                                                                          0.053
                                      KY
                                                                           16.8
                                                                          -19.7
                                                                          -21.6
                                                                           15.1
                                                                           16.6
                                                                            5.7
                                                                          -12.9
                                                                           17.5
                                                                          973.2
                                                                          0.018
                                                                           34.3
                                                                          0.035
                                      MD
                                                                           -3.3
                                                                            2.0
                                                                           -4.9
                                                                            5.0
                                                                            2.7
                                                                            8.9
                                                                          -10.4
                                                                            6.6
                                                                          282.8
                                                                          0.023
                                                                           12.9
                                                                          0.045
                                      MI
                                                                            2.2
                                                                           -5.3
                                                                           -8.7
                                                                           19.0
                                                                          -16.5
                                                                           23.7
                                                                          -14.5
                                                                           15.9
                                                                          741.5
                                                                          0.021
                                                                           31.1
                                                                          0.041
                                      MN
                                                                          -13.3
                                                                           15.9
                                                                           -5.6
                                                                            4.9
                                                                           -0.1
                                                                            8.0
                                                                           -9.8
                                                                           10.4
                                                                          396.9
                                                                          0.026
                                                                           20.4
                                                                          0.051
                                      MO
                                                                          -27.3
                                                                            5.7
                                                                            5.8
                                                                           23.6
                                                                           19.0
                                                                            3.6
                                                                          -30.3
                                                                           21.1
                                                                          790.0
                                                                          0.027
                                                                           41.3
                                                                          0.053
                                      NC
                                                                            9.2
                                                                          -11.3
                                                                           -7.2
                                                                           13.6
                                                                          -14.5
                                                                           18.1
                                                                           -7.9
                                                                           13.2
                                                                          733.6
                                                                          0.018
                                                                           25.9
                                                                          0.035
                                      NE
                                                                           -6.1
                                                                            5.1
                                                                           -2.7
                                                                            8.1
                                                                            2.5
                                                                           -7.2
                                                                            0.3
                                                                            5.7
                                                                          237.2
                                                                          0.024
                                                                           11.2
                                                                          0.047
                                      NJ
                                                                            4.7
                                                                           -8.4
                                                                            3.5
                                                                            0.2
                                                                           -2.6
                                                                            4.6
                                                                           -1.9
                                                                            4.8
                                                                          154.7
                                                                          0.031
                                                                            9.4
                                                                          0.061
                                      NY
                                                                            4.6
                                                                           -4.1
                                                                           -9.3
                                                                          -14.1
                                                                           25.9
                                                                           20.6
                                                                          -23.6
                                                                           18.1
                                                                          337.0
                                                                          0.054
                                                                           35.5
                                                                          0.106
                                      OH
                                                                            4.3
                                                                           21.2
                                                                          -54.6
                                                                           23.3
                                                                           -6.9
                                                                           30.3
                                                                          -17.6
                                                                           29.6
                                                                        1,316.7
                                                                          0.023
                                                                           58.1
                                                                          0.045
                                      PA
                                                                          -17.0
                                                                          -14.0
                                                                           24.2
                                                                           14.7
                                                                            0.8
                                                                           29.5
                                                                          -38.3
                                                                           24.6
                                                                        1,157.7
                                                                          0.021
                                                                           48.2
                                                                          0.041
                                      SC
                                                                            5.0
                                                                          -21.2
                                                                            7.4
                                                                            9.5
                                                                            5.3
                                                                            7.2
                                                                          -13.2
                                                                           12.1
                                                                          445.4
                                                                          0.027
                                                                           23.7
                                                                          0.053
                                      TN
                                                                           27.2
                                                                          -26.1
                                                                          -12.7
                                                                          -10.3
                                                                           12.2
                                                                           24.7
                                                                          -15.0
                                                                           21.1
                                                                          602.9
                                                                          0.035
                                                                           41.3
                                                                          0.069
                                      TX
                                                                          -75.7
                                                                          -23.9
                                                                           59.2
                                                                           89.2
                                                                           18.2
                                                                           33.3
                                                                         -100.2
                                                                           69.8
                                                                        2,561.0
                                                                          0.027
                                                                          136.9
                                                                          0.053
                                      VA
                                                                           10.5
                                                                           -9.0
                                                                           -9.7
                                                                            3.8
                                                                           -8.3
                                                                           25.9
                                                                          -13.2
                                                                           14.2
                                                                          335.7
                                                                          0.042
                                                                           27.9
                                                                          0.082
                                      WI
                                                                          -16.5
                                                                            0.7
                                                                            3.4
                                                                           31.9
                                                                           -5.9
                                                                           -2.3
                                                                          -11.3
                                                                           15.7
                                                                          496.6
                                                                          0.032
                                                                           30.7
                                                                          0.063
                                      WV
                                                                            9.8
                                                                           15.1
                                                                          -26.9
                                                                           -9.8
                                                                          -11.5
                                                                           25.7
                                                                           -2.4
                                                                           18.0
                                                                          873.1
                                                                          0.021
                                                                           35.2
                                                                          0.041

* Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines.

Table 9: Difference between Total Heat Input Measured and Estimated (million MMBtu) from All Three* EGU Categories for Ozone Season Using the Regression Equation.

                                     State
                                     2002
                                     2003
                                     2004
                                     2005
                                     2006
                                     2007
                                     2008
               Standard Deviation of Heat Input (million MMBtu)
                 Average Heat Input (2002-2008 (from Table 3)
                Standard Deviation as a Fraction of Average HI
            95% Confidence Level Variability in HI (million MMBtu)
       95% Confidence Level Variability in HI (as a Fraction of Avg. HI)
                                      AL
                                                                            3.4
                                                                            0.1
                                                                           -9.8
                                                                          -10.8
                                                                           14.1
                                                                           22.5
                                                                          -19.5
                                                                           14.8
                                                                          438.1
                                                                          0.034
                                                                           29.0
                                                                          0.067
                                      AR
                                                                          -12.7
                                                                           10.7
                                                                            2.5
                                                                           -9.7
                                                                           16.8
                                                                            8.6
                                                                          -16.2
                                                                           12.9
                                                                          151.7
                                                                          0.085
                                                                           25.3
                                                                          0.167
                                      FL
                                                                            6.4
                                                                           -7.6
                                                                          -19.6
                                                                           11.8
                                                                           15.3
                                                                           12.2
                                                                          -18.5
                                                                           15.0
                                                                          603.3
                                                                          0.025
                                                                           29.4
                                                                          0.049
                                      GA
                                                                           10.4
                                                                          -25.3
                                                                          -15.9
                                                                           24.0
                                                                           16.9
                                                                           22.2
                                                                          -32.3
                                                                           23.8
                                                                          437.8
                                                                          0.054
                                                                           46.7
                                                                          0.106
                                      IA
                                                                            7.1
                                                                           -5.4
                                                                           -8.8
                                                                            9.4
                                                                           -8.6
                                                                            8.8
                                                                           -2.5
                                                                            8.2
                                                                          174.1
                                                                          0.047
                                                                           16.1
                                                                          0.092
                                      IL
                                                                            7.6
                                                                          -20.4
                                                                           -4.3
                                                                           20.8
                                                                            0.3
                                                                           10.7
                                                                          -14.6
                                                                           14.5
                                                                          457.2
                                                                          0.032
                                                                           28.3
                                                                          0.063
                                      IN
                                                                            4.0
                                                                           -9.1
                                                                          -15.0
                                                                           21.5
                                                                            8.3
                                                                            0.5
                                                                          -10.1
                                                                           12.6
                                                                          556.9
                                                                          0.023
                                                                           24.7
                                                                          0.045
                                      KS
                                                                           -1.3
                                                                           -0.7
                                                                           -2.0
                                                                            4.7
                                                                           -0.9
                                                                            6.9
                                                                           -6.7
                                                                            4.5
                                                                          175.9
                                                                          0.026
                                                                            8.8
                                                                          0.051
                                      KY
                                                                           17.1
                                                                          -18.2
                                                                          -19.4
                                                                           11.8
                                                                           10.5
                                                                            9.3
                                                                          -11.2
                                                                           15.6
                                                                          422.6
                                                                          0.037
                                                                           30.6
                                                                          0.073
                                      LA
                                                                          -18.2
                                                                           -0.1
                                                                           14.4
                                                                           10.5
                                                                           13.5
                                                                           -6.4
                                                                          -13.7
                                                                           13.3
                                                                          139.4
                                                                          0.095
                                                                           26.1
                                                                          0.186
                                      MD
                                                                            6.1
                                                                           -8.6
                                                                           -4.4
                                                                            6.6
                                                                           -0.3
                                                                            4.5
                                                                           -4.0
                                                                            5.9
                                                                          124.9
                                                                          0.047
                                                                           11.6
                                                                          0.092
                                      MI
                                                                           11.4
                                                                           -9.7
                                                                          -19.2
                                                                           13.9
                                                                            0.4
                                                                           14.4
                                                                          -11.2
                                                                           13.7
                                                                          326.0
                                                                          0.042
                                                                           26.8
                                                                          0.082
                                      MO
                                                                           -7.2
                                                                            1.0
                                                                           -0.3
                                                                            4.3
                                                                           11.2
                                                                            4.4
                                                                          -13.3
                                                                            8.1
                                                                          349.9
                                                                          0.023
                                                                           15.8
                                                                          0.045
                                      MS
                                                                            1.1
                                                                           -6.8
                                                                            0.3
                                                                            1.9
                                                                            6.1
                                                                            8.1
                                                                          -10.8
                                                                            6.7
                                                                          135.4
                                                                          0.050
                                                                           13.2
                                                                          0.098
                                      NC
                                                                           15.3
                                                                          -14.3
                                                                          -14.0
                                                                            8.2
                                                                            1.7
                                                                            7.5
                                                                           -4.4
                                                                           11.4
                                                                          333.4
                                                                          0.034
                                                                           22.4
                                                                          0.067
                                      NJ
                                                                            4.8
                                                                           -7.9
                                                                            2.1
                                                                            0.2
                                                                            0.0
                                                                            2.2
                                                                           -1.3
                                                                            4.0
                                                                           75.9
                                                                          0.053
                                                                            7.9
                                                                          0.104
                                      NY
                                                                            2.6
                                                                          -10.5
                                                                           -3.9
                                                                            3.9
                                                                           17.7
                                                                            5.1
                                                                          -14.9
                                                                           10.8
                                                                          148.6
                                                                          0.073
                                                                           21.3
                                                                          0.143
                                      OH
                                                                           16.4
                                                                           -4.5
                                                                          -28.9
                                                                            7.1
                                                                           -5.4
                                                                           29.3
                                                                          -14.0
                                                                           19.4
                                                                          567.3
                                                                          0.034
                                                                           38.0
                                                                          0.067
                                      OK
                                                                           -8.0
                                                                            4.1
                                                                           -6.0
                                                                           15.6
                                                                            4.9
                                                                           -5.3
                                                                           -5.3
                                                                            8.6
                                                                          232.8
                                                                          0.037
                                                                           16.8
                                                                          0.073
                                      PA
                                                                           -4.9
                                                                          -14.1
                                                                           -0.8
                                                                           21.5
                                                                           10.2
                                                                           17.9
                                                                          -29.9
                                                                           18.3
                                                                          507.8
                                                                          0.036
                                                                           35.8
                                                                          0.071
                                      SC
                                                                           11.1
                                                                          -19.1
                                                                            1.7
                                                                            5.5
                                                                            1.5
                                                                            2.8
                                                                           -3.4
                                                                            9.5
                                                                          208.7
                                                                          0.046
                                                                           18.6
                                                                          0.090
                                      TN
                                                                           22.9
                                                                          -23.9
                                                                          -11.8
                                                                            2.2
                                                                            5.5
                                                                           11.3
                                                                           -6.3
                                                                           15.5
                                                                          267.9
                                                                          0.058
                                                                           30.3
                                                                          0.114
                                      TX
                                                                          -35.5
                                                                          -16.5
                                                                           24.5
                                                                           44.5
                                                                           31.8
                                                                            0.1
                                                                          -49.0
                                                                           35.4
                                                                        1,184.6
                                                                          0.030
                                                                           69.4
                                                                          0.059
                                      VA
                                                                            5.8
                                                                           -7.1
                                                                           -3.0
                                                                            0.6
                                                                           -2.1
                                                                           14.5
                                                                           -8.8
                                                                            8.0
                                                                          153.7
                                                                          0.052
                                                                           15.7
                                                                          0.102
                                      WI
                                                                            0.5
                                                                           -7.0
                                                                          -10.8
                                                                           21.6
                                                                            4.5
                                                                            1.3
                                                                          -10.2
                                                                           11.3
                                                                          218.3
                                                                          0.052
                                                                           22.1
                                                                          0.102
                                      WV
                                                                            2.2
                                                                            7.6
                                                                          -15.3
                                                                           -0.4
                                                                           -2.2
                                                                           15.5
                                                                           -7.4
                                                                           10.0
                                                                          375.8
                                                                          0.027
                                                                           19.5
                                                                          0.053

* Coal-fired units; combined cycle turbines; and a combination of oil- and gas-fired boilers and simple-cycle combustion turbines

       

      (c) Estimation of variability in emissions using the year-to-year variability in historical heat input. 
      The analysis described in the sections above results in estimated 95% confidence level historic variabilities in heat input for each state and pollutant (Tables 7, 8, and 9).  As described in the preamble in section VI.E.2, from these variability values, EPA identified a specific variability percentage level for each state (Table 10).  This was typically 10%, unless the state's historic heat input variability was higher than 10%.  In those cases, EPA rounded those budgets' variability limit percentages up to the next five-percent increment (e.g., 15 percent, 20 percent) that successfully accommodated the historically observed variability, up to a maximum of 20%.  The relationship between the historic variability values and the variability percentage levels can be found in Table 10.
      As described in section VI.E.2 of the preamble, the final step in estimating state-by-state year-to-year (1-year) variability in emissions is to convert the variability percentage level in each state into variability in pollutant emissions (i.e., a "variability limit").  EPA did this by multiplying the variability percentage level in each state for each pollutant by the state emissions budgets for each pollutant (section VI.D of the preamble discusses EPA's approach to determine the final Transport Rule budgets, and lists the budgets in Tables VI.D-3 and VI.D-4).  For each state, Tables VI.F-1, VI.F-2, and VI.F-3 list the resulting variability limits for each state for SO2, annual NOX and ozone-season NOX, respectively.

Table 10. Relationship between 95% Confidence Level Historic Variability in Heat Input and Variability Limit Used in the Transport Rule*.
                                       
                                      SO2
                                  Annual NOX
                               Ozone-Season NOX
                                     State
                             Historic Variability
                       Transport Rule Variability Limit
                             Historic Variability
                       Transport Rule Variability Limit
                             Historic Variability
                       Transport Rule Variability Limit
                                      AL
                                     5.9%
                                      10%
                                     4.9%
                                      10%
                                     6.7%
                                      10%
                                      AR
                                       
                                       
                                       
                                       
                                     16.7%
                                      20%
                                      FL
                                       
                                       
                                       
                                       
                                     4.9%
                                      10%
                                      GA
                                     5.9%
                                      10%
                                     8.4%
                                      10%
                                     10.6%
                                      15%
                                      IL
                                     4.1%
                                      10%
                                     3.9%
                                      10%
                                     6.3%
                                      10%
                                      IN
                                     2.7%
                                      10%
                                     2.5%
                                      10%
                                     4.5%
                                      10%
                                      IA*
                                     7.3%
                                      10%
                                     6.1%
                                      10%
                                     9.2%
                                      10%
                                      KS*
                                     5.3%
                                      10%
                                     5.3%
                                      10%
                                     5.1%
                                      10%
                                      KY
                                     2.5%
                                      10%
                                     3.5%
                                      10%
                                     7.3%
                                      10%
                                      LA
                                       
                                       
                                       
                                       
                                     18.6%
                                      20%
                                      MD
                                     4.5%
                                      10%
                                     4.5%
                                      10%
                                     9.2%
                                      10%
                                      MI*
                                     2.9%
                                      10%
                                     4.1%
                                      10%
                                     8.2%
                                      10%
                                      MN
                                     4.5%
                                      10%
                                     5.1%
                                      10%
                                       
                                       
                                      MS
                                       
                                       
                                       
                                       
                                     9.8%
                                      10%
                                      MO*
                                     6.1%
                                      10%
                                     5.3%
                                      10%
                                     4.5%
                                      10%
                                      NE
                                     4.9%
                                      10%
                                     4.7%
                                      10%
                                       
                                       
                                      NJ
                                      20%
                                      20%
                                     6.1%
                                      10%
                                     10.4%
                                      15%
                                      NY
                                     6.7%
                                      10%
                                     10.6%
                                      15%
                                     14.3%
                                      15%
                                      NC
                                     2.7%
                                      10%
                                     3.5%
                                      10%
                                     6.7%
                                      10%
                                      OH
                                     3.7%
                                      10%
                                     4.5%
                                      10%
                                     6.7%
                                      10%
                                      OK*
                                       
                                       
                                       
                                       
                                     7.3%
                                      10%
                                      PA
                                     3.7%
                                      10%
                                     4.1%
                                      10%
                                     7.1%
                                      10%
                                      SC
                                     2.4%
                                      10%
                                     5.3%
                                      10%
                                     9.0%
                                      10%
                                      TN
                                     6.3%
                                      10%
                                     6.9%
                                      10%
                                     11.4%
                                      15%
                                      TX
                                     2.5%
                                      10%
                                     5.3%
                                      10%
                                     5.9%
                                      10%
                                      VA
                                     7.3%
                                      10%
                                     8.2%
                                      10%
                                     10.2%
                                      15%
                                      WV
                                     3.9%
                                      10%
                                     4.1%
                                      10%
                                     5.3%
                                      10%
                                      WI*
                                     4.9%
                                      10%
                                     6.3%
                                      10%
                                     10.2%
                                      15%
*Indicates a state (IA, KS, MI, OK, WI, and MO) that is included in the supplemental notice of proposed rulemaking for ozone-season NOx emission reductions. See the preamble for details.

3. Numerical simulation of 1- and 3-year variability
      For the reasons discussed in section VI.E of the preamble, although EPA proposed to implement both 1-year variability limits and 3-year average variability limits, the final Transport Rule includes only the 1-year limits.  In the proposal, EPA first established 1-year variability limits (following the procedure outlined above) and then established corresponding 3-year variability limits to be statistically indistinguishable from the 1-year variability limits.  In other words, the proposal's 3-year variability limits were calculated on a statistical basis to offer states the same degree of future variability (based on historic variability) as the 1-year variability limits.  For the final rule, EPA analyzed the relationship between the 1-year and 3-year variability limits, performing a numerical verification of equal likelihood of potential violations of a state's assurance level when evaluating random variation (10% at the 95% two-tailed confidence level) around a constant budget. 
      As discussed in section VI.E of the final Transport Rule preamble, the state-by-state emissions budgets are based on the availability of emission reductions at an equal cost threshold (within each of the programs).  As such, EPA expects the sources in each covered state to make these cost-effective reductions and to meet the emission budgets each year.  On average EPA does not expect any systematic bias in emissions (against the established state budgets) to occur.  Thus, a non-biased assessment of variability is appropriate.  EPA simulated 1- and 3-year variation around a constant budget for a hypothetical state, and found, as described below, comparable results affirming that on a statistical basis, the 3-year variability limits are no more likely to be exceeded than the 1-year variability limits.
      Using a random-number generator within Microsoft Excel, EPA numerically simulated random variation using the 95% two-tailed confidence level 1-year variability of 10%.  The 1-year variability standard deviation is 10% divided by 1.960, or 5.1%.   Using the formula, =NORMINV(RAND(),100,(10/1.960)), EPA simulated yearly emissions for a "state" with a budget of 100, with random variation of 5.1%.  EPA simulated five consecutive "years" of emissions, then calculated three 3-year consecutive averages ("years" 1, 2, and 3; 2, 3, and 4; and 3, 4, and 5) .  EPA, then, assessed the average number of "exceedances" of the 1-year and 3-year "budgets plus variability limits".  The 1-year budget plus variability limit is 110, while the 3-year budget plus variability limit (as defined in the proposal) is 105.77.  EPA simulated 10,000 5-year time-periods, and averaged the number of exceedances of the 1-year (50,000 data points) and 3-year limits (30,000 data points).  For both the 1-year and 3-year cases, the average number of exceedances was 2.5%, conforming to the expected 95% two-tailed confidence exceedance value of 2.5%.
      This finding confirms that the proposed 3-year variability limits are statistically indistinguishable from the 1-year variability limits for each state; therefore, EPA has determined that the 3-year variability limits are redundant with the 1-year variability limits and are thus unnecessary.
      
      4. Results of an analysis using the air quality assessment tool
      The objective of this section is to estimate the possible effects on air quality in 2014 of the variability limits. This analysis used the air quality assessment tool, or AQAT, and state-by-state emissions to estimate downwind state-by-state air quality contributions at receptors with nonattainment and maintenance problems in the CAMx air quality modeling of 2012 base case (section VI.C of the final Transport Rule preamble discusses AQAT; section V of the final Transport Rule preamble discusses air quality modeling).  This analysis is similar to the analyses performed for the proposed Transport Rule (and reported in the proposed Transport Rule "Power Sector Variability" TSD).  It concludes that, as estimated using AQAT, while variability in power system operation (and thereby SO2 emissions from EGUs under the Transport Rule) does have perceptible downwind air quality effects on PM2.5 concentrations, these effects are minimal.  EPA believes that variation in other factors such as SO2 and NOx emission patterns from non-EGU sources, contributions from other pollutants (i.e., ammonia, elemental and organic carbon for PM2.5 and volatile organic carbon for ozone), and meteorological factors play important roles in downwind air quality.
      For this analysis, EPA varied the EGU SO2 emissions of upwind states included in the final Transport Rule that are "linked" to downwind receptors (as described in section V of the preamble).  The variation in emissions was designed to reflect the allowance of inherent year-to-year (1-year) variability in power system operations above average state-level emissions equal to the $2,300/ton and $500/ton SO2 cost thresholds for group 1 and group 2 states respectively ("$2,300/ton" for the purposes of this discussion).  Details on this scenario (TR_SO2_2300_Final) can be found in appendix A of the Significant Contribution and State Emissions Budgets Final Rule TSD.  EPA estimated the air quality impacts using the change in the maximum daily PM2.5 design value.   This analysis focused on variability limits related to annual SO2 emissions and the 24-hour PM2.5 concentrations for the same reasons listed in the proposed Transport Rule "Power Sector Variability" TSD, with the addition that the improved "calibrated" AQAT used in the final Transport Rule only allows SO2 emissions to be varied for estimating downwind ammonium sulfate concentrations (which is discussed further in section VI.C in the final rule's preamble).
      In contrast to the analyses in the proposed Transport Rule, this analysis focuses on the "worst-case" emissions variability in 2014.  This is intended to estimate upper bounds for the effects of year-to-year variability in power system operations on air quality.   For this analysis, the "worst case" situation is defined as the hypothetical scenario in which all states that are linked to a particular receptor increase their SO2 emissions to a "variability maximum" equal to the 2014 emissions equal to the final Transport Rule cost thresholds plus a fixed percentage (variability level) of the state budget.  States that were not linked to the receptor were held at base case SO2 emission levels.  Four variability levels were examined (5, 10, 15, and 20%).  These levels were chosen to bracket the variability level selected for most states (i.e., 10%).  To be consistent with the analysis of significant contribution and interference with maintenance, the SO2 emissions from the state containing the receptor were also increased to the final Transport Rule cost thresholds plus variability level.  A second assessment of this analysis focused on the effects of variation in emissions due only to the upwind states.  The emissions from the state containing the receptor (home state) were maintained at a constant level, equal to its final Transport Rule cost threshold.  By comparing the two assessments it is possible to get a sense of the relative importance of variation of upwind power system operations compared with variation in the home state's power system operations.
      This variability analysis does not balance emission increases in some states with emission decreases in other states (as was done in the analysis for the proposed Transport Rule).  Specifically, this analysis does not account for corresponding decreases from other states included in the final Transport Rule which are not contributing above the 1% threshold to a particular receptor.  
      EPA specifically notes that this analysis is intended to demonstrate the potential air quality impacts from year-to-year variability under "extreme" worst-case scenarios, where states linked to a downwind receptor simultaneously need to utilize the maximum power sector variability; it is distinct from the "typical" operating conditions represented in an "average" year under which significant contribution and interference with maintenance are examined to inform EPA's determination of emission reductions available at various cost thresholds. In other words, the Transport Rule state budgets are established on the basis of conditions in an average year, while the variability provisions address the inherent year-to-year fluctuations of power sector operations around those average conditions.    This analysis examines the fluctuations in downwind air quality that may be attributable to various potential degrees of year-to-year power sector emission variability around upwind state budgets.  Such an analysis is fundamentally different from the Transport Rule's analysis to determine significant contribution and interference with maintenance, which includes an examination of downwind air quality impacts not on a fluctuating year-to-year basis, but on the basis of the degree of stringency of upwind emissions control under expected (i.e., average) operating conditions as represented by EPA's power sector modeling projections.  Therefore, the results of this TSD's analysis are not pertinent to the Agency's consideration of downwind air quality impacts as one factor in its multifactor analysis of significant contribution and interference with maintenance.
      The results of the analysis can be found in Table 11 and in Figure 1, below.  The estimated increases in maximum design value PM2.5 concentrations across the range of variability levels examined are relatively small, with a maximum of 0.57 g/m[3] at 20% variability for Jefferson County, AL.  Averaged across the receptors with nonattainment and maintenance problems in the CAMx air quality modeling of the 2012, the increase was 0.29 g/m[3] at 20% variability.  For the second variation of the analysis, when the home state emissions are held constant at the final Transport Rule cost threshold, the increase averaged 0.19 g/m[3].  (Table 11 and Figure 2).   The maximal increase was 0.41g/m[3] for receptor number 420031008 in Allegheny, Pennsylvania.  For most locations, the largest contributor to increased PM2.5 concentration from a single upwind state will be from sources within the state containing the receptor itself (this conclusion is drawn from comparing the Worst Case (All States) and Worst Case (Upwind States) columns in Table 22 from the "Power Sector Variability" TSD from the proposed Transport Rule as well as by comparing the difference in air quality estimates between 0 and 20% variation for the two cases (compare the differences from Tables 11 and 12).
      

*The six sites are Allegheny, PA (64); Lancaster, PA (07); Wayne, MI (16 and 19); Cook, IL (16); and Lake, IN (22). 
**The eight sites include the six sites listed above as well as Cuyahoga, OH (38) and Wayne, MI (33).


Figure 1.  Increase in maximum PM2.5 design value (g/m[3]) in 2014 at the $2300/ton cost threshold level as the variability level is increased from 0 to 20 percent, individually for the eight sites (left panel) as well as for various combinations of sites (right panel).  The combinations of sites can be found in Table 10.
      

Table 11. Maximum PM2.5 DVs (g/m[3]) in 2014 With Linked States at the Final Transport Rule Cost Threshold Level with Various Additional Amounts of Emissions Due to Variability.
                                    Site ID
                                     State
                                    County
                                Variability (%)
Difference in air quality between the 0% variability level and another level. 
                                       
                                       
                                       
                                       0
                                       5
                                      10
                                      15
                                      20
                                       0
                                       5
                                      10
                                      15
                                      20
avg. of 6 sites*
                                                                          38.39
                                                                          38.44
                                                                          38.50
                                                                          38.55
                                                                          38.60
                                                                           0.00
                                                                           0.05
                                                                           0.11
                                                                           0.16
                                                                           0.21
avg. of 8 sites**
                                                                          37.62
                                                                          37.68
                                                                          37.74
                                                                          37.80
                                                                          37.85
                                                                           0.00
                                                                           0.06
                                                                           0.12
                                                                           0.17
                                                                           0.23
max of all 2012 base case
                                                                          48.63
                                                                          48.72
                                                                          48.85
                                                                          48.97
                                                                          49.09
                                                                           0.00
                                                                           0.14
                                                                           0.29
                                                                           0.44
                                                                           0.57
                                   420030064
                                 Pennsylvania
                                   Allegheny
                                     48.63
                                     48.72
                                     48.85
                                     48.97
                                     49.09
                                     0.00
                                     0.09
                                     0.21
                                     0.34
                                     0.46
                                   420030093
                                 Pennsylvania
                                   Allegheny
                                     34.80
                                     34.90
                                     35.01
                                     35.11
                                     35.21
                                     0.00
                                     0.10
                                     0.21
                                     0.31
                                     0.41
                                   390350038
                                     Ohio
                                   Cuyahoga
                                     35.41
                                     35.44
                                     35.47
                                     35.50
                                     35.53
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   261630016
                                   Michigan
                                     Wayne
                                     35.65
                                     35.69
                                     35.73
                                     35.77
                                     35.81
                                     0.00
                                     0.04
                                     0.08
                                     0.12
                                     0.16
                                   390350060
                                     Ohio
                                   Cuyahoga
                                     33.04
                                     33.10
                                     33.14
                                     33.16
                                     33.18
                                     0.00
                                     0.06
                                     0.10
                                     0.12
                                     0.15
                                   170311016
                                   Illinois
                                     Cook
                                     36.54
                                     36.62
                                     36.70
                                     36.78
                                     36.85
                                     0.00
                                     0.08
                                     0.16
                                     0.24
                                     0.31
                                   261630033
                                   Michigan
                                     Wayne
                                     35.23
                                     35.35
                                     35.46
                                     35.58
                                     35.69
                                     0.00
                                     0.12
                                     0.23
                                     0.35
                                     0.46
                                   180890022
                                    Indiana
                                     Lake
                                     36.51
                                     36.57
                                     36.61
                                     36.64
                                     36.67
                                     0.00
                                     0.07
                                     0.10
                                     0.14
                                     0.17
                                   540090011
                                 West Virginia
                                    Brooke
                                     30.02
                                     30.14
                                     30.26
                                     30.38
                                     30.49
                                     0.00
                                     0.12
                                     0.24
                                     0.36
                                     0.47
                                   420710007
                                 Pennsylvania
                                   Lancaster
                                     37.18
                                     37.19
                                     37.20
                                     37.21
                                     37.22
                                     0.00
                                     0.01
                                     0.02
                                     0.03
                                     0.04
                                   390350045
                                     Ohio
                                   Cuyahoga
                                     27.60
                                     27.67
                                     27.75
                                     27.83
                                     27.90
                                     0.00
                                     0.08
                                     0.15
                                     0.23
                                     0.31
                                   390811001
                                     Ohio
                                   Jefferson
                                     28.03
                                     28.14
                                     28.26
                                     28.37
                                     28.49
                                     0.00
                                     0.12
                                     0.23
                                     0.35
                                     0.46
                                   261630019
                                   Michigan
                                     Wayne
                                     35.83
                                     35.86
                                     35.89
                                     35.92
                                     35.95
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   390350065
                                     Ohio
                                   Cuyahoga
                                     27.00
                                     27.10
                                     27.20
                                     27.30
                                     27.41
                                     0.00
                                     0.10
                                     0.20
                                     0.30
                                     0.41
                                   170313301
                                   Illinois
                                     Cook
                                     32.84
                                     32.90
                                     32.95
                                     33.01
                                     33.07
                                     0.00
                                     0.06
                                     0.11
                                     0.17
                                     0.22
                                   420070014
                                 Pennsylvania
                                    Beaver
                                     28.70
                                     28.77
                                     28.86
                                     28.96
                                     29.06
                                     0.00
                                     0.06
                                     0.16
                                     0.26
                                     0.36
                                   420033007
                                 Pennsylvania
                                   Allegheny
                                     28.81
                                     28.90
                                     28.99
                                     29.08
                                     29.17
                                     0.00
                                     0.09
                                     0.18
                                     0.27
                                     0.37
                                   010730023
                                    Alabama
                                   Jefferson
                                     32.12
                                     32.26
                                     32.41
                                     32.55
                                     32.69
                                     0.00
                                     0.14
                                     0.29
                                     0.44
                                     0.57
                                   550790026
                                   Wisconsin
                                   Milwaukee
                                     33.21
                                     33.26
                                     33.31
                                     33.36
                                     33.42
                                     0.00
                                     0.05
                                     0.11
                                     0.16
                                     0.21
                                   180970043
                                    Indiana
                                    Marion
                                     27.82
                                     27.91
                                     28.00
                                     28.09
                                     28.18
                                     0.00
                                     0.09
                                     0.18
                                     0.27
                                     0.35
                                   261470005
                                   Michigan
                                   St Clair
                                     33.38
                                     33.41
                                     33.44
                                     33.47
                                     33.51
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.13
                                   550790043
                                   Wisconsin
                                   Milwaukee
                                     33.92
                                     33.96
                                     34.00
                                     34.04
                                     34.07
                                     0.00
                                     0.04
                                     0.08
                                     0.12
                                     0.15
                                   180890026
                                    Indiana
                                     Lake
                                     33.37
                                     33.40
                                     33.44
                                     33.47
                                     33.50
                                     0.00
                                     0.03
                                     0.07
                                     0.10
                                     0.14
                                   180970081
                                    Indiana
                                    Marion
                                     27.59
                                     27.72
                                     27.83
                                     27.94
                                     28.05
                                     0.00
                                     0.13
                                     0.24
                                     0.35
                                     0.46
                                   180970066
                                    Indiana
                                    Marion
                                     29.13
                                     29.27
                                     29.40
                                     29.51
                                     29.62
                                     0.00
                                     0.14
                                     0.28
                                     0.38
                                     0.49
                                   171191007
                                   Illinois
                                    Madison
                                     30.66
                                     30.76
                                     30.82
                                     30.88
                                     30.95
                                     0.00
                                     0.10
                                     0.16
                                     0.22
                                     0.28
                                   550790010
                                   Wisconsin
                                   Milwaukee
                                     33.13
                                     33.18
                                     33.23
                                     33.29
                                     33.34
                                     0.00
                                     0.05
                                     0.11
                                     0.16
                                     0.21
                                   390170003
                                     Ohio
                                    Butler
                                     27.33
                                     27.42
                                     27.53
                                     27.65
                                     27.76
                                     0.00
                                     0.09
                                     0.20
                                     0.32
                                     0.43
                                   170316005
                                   Illinois
                                     Cook
                                     34.82
                                     34.86
                                     34.90
                                     34.95
                                     34.99
                                     0.00
                                     0.04
                                     0.09
                                     0.13
                                     0.18
                                   420031008
                                 Pennsylvania
                                   Allegheny
                                     25.62
                                     25.76
                                     25.89
                                     26.03
                                     26.17
                                     0.00
                                     0.14
                                     0.27
                                     0.41
                                     0.54
                                   261610008
                                   Michigan
                                   Washtenaw
                                     29.33
                                     29.36
                                     29.40
                                     29.43
                                     29.47
                                     0.00
                                     0.03
                                     0.07
                                     0.10
                                     0.14
                                   170312001
                                   Illinois
                                     Cook
                                     32.33
                                     32.38
                                     32.44
                                     32.49
                                     32.54
                                     0.00
                                     0.05
                                     0.10
                                     0.15
                                     0.20
                                   170310052
                                   Illinois
                                     Cook
                                     30.31
                                     30.36
                                     30.40
                                     30.45
                                     30.49
                                     0.00
                                     0.04
                                     0.09
                                     0.13
                                     0.18
                                   421330008
                                 Pennsylvania
                                     York
                                     33.91
                                     33.94
                                     33.97
                                     34.00
                                     34.03
                                     0.00
                                     0.03
                                     0.06
                                     0.08
                                     0.11
                                   261630015
                                   Michigan
                                     Wayne
                                     31.99
                                     32.04
                                     32.08
                                     32.14
                                     32.25
                                     0.00
                                     0.04
                                     0.09
                                     0.15
                                     0.26
                                   010732003
                                    Alabama
                                   Jefferson
                                     31.91
                                     31.99
                                     32.06
                                     32.13
                                     32.20
                                     0.00
                                     0.07
                                     0.15
                                     0.22
                                     0.29
                                   390618001
                                     Ohio
                                   Hamilton
                                     26.73
                                     26.81
                                     26.89
                                     26.98
                                     27.06
                                     0.00
                                     0.08
                                     0.17
                                     0.25
                                     0.33
                                   171190023
                                   Illinois
                                    Madison
                                     29.50
                                     29.57
                                     29.65
                                     29.72
                                     29.79
                                     0.00
                                     0.07
                                     0.15
                                     0.22
                                     0.29
                                   420031301
                                 Pennsylvania
                                   Allegheny
                                     26.15
                                     26.23
                                     26.30
                                     26.38
                                     26.45
                                     0.00
                                     0.08
                                     0.15
                                     0.23
                                     0.30
                                   391130032
                                     Ohio
                                  Montgomery
                                     24.62
                                     24.70
                                     24.79
                                     24.87
                                     24.96
                                     0.00
                                     0.09
                                     0.17
                                     0.26
                                     0.34
                                   420030116
                                 Pennsylvania
                                   Allegheny
                                     26.34
                                     26.42
                                     26.50
                                     26.59
                                     26.67
                                     0.00
                                     0.08
                                     0.17
                                     0.25
                                     0.33
*The six sites are Allegheny, PA (64); Lancaster, PA (07); Wayne, MI (16 and 19); Cook, IL (16); and Lake, IN (22). 
**The eight sites include the six sites listed above as well as Cuyahoga, OH (38) and Wayne, MI (33).
      
      


Table 12. Maximum PM2.5 DVs (g/m[3]) in 2014 with Linked States at the Final Transport Rule Cost Threshold Level with Various Additional Amounts of Emissions Due to Variability with the Home State Held Constant with No Variability at the 2014 Final Transport Rule Cost Threshold. 
                                    Site ID
                                     State
                                    County
                                Variability (%)
Difference in air quality between the 0% variability level and another level. 
                                       
                                       
                                       
                                       0
                                       5
                                      10
                                      15
                                      20
                                       0
                                       5
                                      10
                                      15
                                      20
avg. of 6 sites*
                                                                          38.39
                                                                          38.42
                                                                          38.46
                                                                          38.49
                                                                          38.52
                                                                           0.00
                                                                           0.03
                                                                           0.07
                                                                           0.10
                                                                           0.13
avg. of 8 sites**
                                                                          37.62
                                                                          37.66
                                                                          37.69
                                                                          37.73
                                                                          37.76
                                                                           0.00
                                                                           0.03
                                                                           0.07
                                                                           0.10
                                                                           0.14
max of all 2012 base case
                                                                          48.63
                                                                          48.69
                                                                          48.78
                                                                          48.87
                                                                          48.95
                                                                           0.00
                                                                           0.10
                                                                           0.21
                                                                           0.31
                                                                           0.41
                                   420030064
                                 Pennsylvania
                                   Allegheny
                                     48.63
                                     48.69
                                     48.78
                                     48.87
                                     48.95
                                     0.00
                                     0.06
                                     0.14
                                     0.23
                                     0.32
                                   420030093
                                 Pennsylvania
                                   Allegheny
                                     34.80
                                     34.88
                                     34.95
                                     35.03
                                     35.10
                                     0.00
                                     0.08
                                     0.15
                                     0.23
                                     0.30
                                   390350038
                                     Ohio
                                   Cuyahoga
                                     35.41
                                     35.42
                                     35.44
                                     35.46
                                     35.47
                                     0.00
                                     0.02
                                     0.03
                                     0.05
                                     0.06
                                   261630016
                                   Michigan
                                     Wayne
                                     35.65
                                     35.67
                                     35.68
                                     35.69
                                     35.70
                                     0.00
                                     0.01
                                     0.02
                                     0.04
                                     0.05
                                   390350060
                                     Ohio
                                   Cuyahoga
                                     33.04
                                     33.07
                                     33.11
                                     33.13
                                     33.14
                                     0.00
                                     0.04
                                     0.07
                                     0.09
                                     0.10
                                   170311016
                                   Illinois
                                     Cook
                                     36.54
                                     36.60
                                     36.67
                                     36.73
                                     36.79
                                     0.00
                                     0.06
                                     0.13
                                     0.19
                                     0.25
                                   261630033
                                   Michigan
                                     Wayne
                                     35.23
                                     35.29
                                     35.35
                                     35.41
                                     35.47
                                     0.00
                                     0.06
                                     0.12
                                     0.18
                                     0.24
                                   180890022
                                    Indiana
                                     Lake
                                     36.51
                                     36.55
                                     36.58
                                     36.60
                                     36.62
                                     0.00
                                     0.05
                                     0.07
                                     0.09
                                     0.11
                                   540090011
                                 West Virginia
                                    Brooke
                                     30.02
                                     30.12
                                     30.21
                                     30.31
                                     30.41
                                     0.00
                                     0.10
                                     0.19
                                     0.29
                                     0.39
                                   420710007
                                 Pennsylvania
                                   Lancaster
                                     37.18
                                     37.18
                                     37.18
                                     37.19
                                     37.19
                                     0.00
                                     0.00
                                     0.01
                                     0.01
                                     0.02
                                   390350045
                                     Ohio
                                   Cuyahoga
                                     27.60
                                     27.64
                                     27.69
                                     27.74
                                     27.79
                                     0.00
                                     0.05
                                     0.09
                                     0.14
                                     0.19
                                   390811001
                                     Ohio
                                   Jefferson
                                     28.03
                                     28.11
                                     28.19
                                     28.27
                                     28.35
                                     0.00
                                     0.08
                                     0.16
                                     0.25
                                     0.33
                                   261630019
                                   Michigan
                                     Wayne
                                     35.83
                                     35.84
                                     35.86
                                     35.87
                                     35.88
                                     0.00
                                     0.01
                                     0.03
                                     0.04
                                     0.06
                                   390350065
                                     Ohio
                                   Cuyahoga
                                     27.00
                                     27.06
                                     27.13
                                     27.19
                                     27.26
                                     0.00
                                     0.06
                                     0.13
                                     0.19
                                     0.26
                                   170313301
                                   Illinois
                                     Cook
                                     32.84
                                     32.88
                                     32.93
                                     32.97
                                     33.01
                                     0.00
                                     0.04
                                     0.08
                                     0.13
                                     0.17
                                   420070014
                                 Pennsylvania
                                    Beaver
                                     28.70
                                     28.75
                                     28.82
                                     28.90
                                     28.99
                                     0.00
                                     0.05
                                     0.12
                                     0.20
                                     0.29
                                   420033007
                                 Pennsylvania
                                   Allegheny
                                     28.81
                                     28.87
                                     28.93
                                     29.00
                                     29.06
                                     0.00
                                     0.06
                                     0.13
                                     0.19
                                     0.26
                                   010730023
                                    Alabama
                                   Jefferson
                                     32.12
                                     32.15
                                     32.19
                                     32.22
                                     32.26
                                     0.00
                                     0.03
                                     0.07
                                     0.10
                                     0.14
                                   550790026
                                   Wisconsin
                                   Milwaukee
                                     33.21
                                     33.25
                                     33.30
                                     33.34
                                     33.38
                                     0.00
                                     0.04
                                     0.09
                                     0.13
                                     0.18
                                   180970043
                                    Indiana
                                    Marion
                                     27.82
                                     27.87
                                     27.93
                                     27.98
                                     28.03
                                     0.00
                                     0.05
                                     0.11
                                     0.16
                                     0.21
                                   261470005
                                   Michigan
                                   St Clair
                                     33.38
                                     33.40
                                     33.42
                                     33.44
                                     33.45
                                     0.00
                                     0.02
                                     0.04
                                     0.05
                                     0.07
                                   550790043
                                   Wisconsin
                                   Milwaukee
                                     33.92
                                     33.95
                                     33.98
                                     34.01
                                     34.04
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   180890026
                                    Indiana
                                     Lake
                                     33.37
                                     33.39
                                     33.42
                                     33.44
                                     33.46
                                     0.00
                                     0.02
                                     0.05
                                     0.07
                                     0.10
                                   180970081
                                    Indiana
                                    Marion
                                     27.59
                                     27.67
                                     27.74
                                     27.80
                                     27.85
                                     0.00
                                     0.08
                                     0.15
                                     0.21
                                     0.27
                                   180970066
                                    Indiana
                                    Marion
                                     29.13
                                     29.22
                                     29.30
                                     29.37
                                     29.43
                                     0.00
                                     0.09
                                     0.17
                                     0.24
                                     0.30
                                   171191007
                                   Illinois
                                    Madison
                                     30.66
                                     30.75
                                     30.80
                                     30.85
                                     30.90
                                     0.00
                                     0.09
                                     0.14
                                     0.19
                                     0.24
                                   550790010
                                   Wisconsin
                                   Milwaukee
                                     33.13
                                     33.17
                                     33.22
                                     33.26
                                     33.31
                                     0.00
                                     0.04
                                     0.09
                                     0.13
                                     0.18
                                   390170003
                                     Ohio
                                    Butler
                                     27.33
                                     27.39
                                     27.48
                                     27.56
                                     27.65
                                     0.00
                                     0.06
                                     0.15
                                     0.24
                                     0.32
                                   170316005
                                   Illinois
                                     Cook
                                     34.82
                                     34.85
                                     34.88
                                     34.91
                                     34.93
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   420031008
                                 Pennsylvania
                                   Allegheny
                                     25.62
                                     25.72
                                     25.83
                                     25.93
                                     26.03
                                     0.00
                                     0.10
                                     0.21
                                     0.31
                                     0.41
                                   261610008
                                   Michigan
                                   Washtenaw
                                     29.33
                                     29.35
                                     29.38
                                     29.40
                                     29.42
                                     0.00
                                     0.02
                                     0.05
                                     0.07
                                     0.09
                                   170312001
                                   Illinois
                                     Cook
                                     32.33
                                     32.38
                                     32.42
                                     32.46
                                     32.50
                                     0.00
                                     0.04
                                     0.08
                                     0.12
                                     0.16
                                   170310052
                                   Illinois
                                     Cook
                                     30.31
                                     30.34
                                     30.37
                                     30.40
                                     30.43
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   421330008
                                 Pennsylvania
                                     York
                                     33.91
                                     33.93
                                     33.94
                                     33.95
                                     33.97
                                     0.00
                                     0.01
                                     0.03
                                     0.04
                                     0.05
                                   261630015
                                   Michigan
                                     Wayne
                                     31.99
                                     32.01
                                     32.02
                                     32.04
                                     32.06
                                     0.00
                                     0.02
                                     0.03
                                     0.05
                                     0.06
                                   010732003
                                    Alabama
                                   Jefferson
                                     31.91
                                     31.94
                                     31.97
                                     32.00
                                     32.03
                                     0.00
                                     0.03
                                     0.06
                                     0.09
                                     0.12
                                   390618001
                                     Ohio
                                   Hamilton
                                     26.73
                                     26.79
                                     26.85
                                     26.91
                                     26.97
                                     0.00
                                     0.06
                                     0.12
                                     0.18
                                     0.24
                                   171190023
                                   Illinois
                                    Madison
                                     29.50
                                     29.56
                                     29.62
                                     29.68
                                     29.73
                                     0.00
                                     0.06
                                     0.12
                                     0.17
                                     0.23
                                   420031301
                                 Pennsylvania
                                   Allegheny
                                     26.15
                                     26.21
                                     26.27
                                     26.32
                                     26.38
                                     0.00
                                     0.06
                                     0.11
                                     0.17
                                     0.23
                                   391130032
                                     Ohio
                                  Montgomery
                                     24.62
                                     24.69
                                     24.75
                                     24.82
                                     24.89
                                     0.00
                                     0.07
                                     0.13
                                     0.20
                                     0.27
                                   420030116
                                 Pennsylvania
                                   Allegheny
                                     26.34
                                     26.40
                                     26.46
                                     26.53
                                     26.59
                                     0.00
                                     0.06
                                     0.12
                                     0.19
                                     0.25
*The six sites are Allegheny, PA (64); Lancaster, PA (07); Wayne, MI (16 and 19); Cook, IL (16); and Lake, IN (22). 
**The eight sites include the six sites listed above as well as Cuyahoga, OH (38) and Wayne, MI (33).



*The six sites are Allegheny, PA (64); Lancaster, PA (07); Wayne, MI (16 and 19); Cook, IL (16); and Lake, IN (22). 
**The eight sites include the six sites listed above as well as Cuyahoga, OH (38) and Wayne, MI (33).

Figure 2.  Increase in maximum PM2.5  design value (g/m[3]) in 2014 at the $2300/ton cost threshold level as the variability level is increased from 0 to 20 percent, individually for the eight sites (left panel) as well as for various combinations of sites (right panel).  The combinations of sites can be found in Table 10.  The state containing the receptor is held constant with no variability at the 2014 $2300/ton cost emission level.
      
      In conclusion, EPA found that, while allowing for the limited variability  to accommodate inherent fluctuations in reliable operation of the power sector (typically 10%), the downwind air quality impacts are small.  At even higher levels of variability (i.e., 20%), the air quality impacts remain small.  This suggests that even under a program allowing substantial year-to-year variability around a budget in any given state's power sector emissions (i.e., 20%), the downwind air quality goals of the program are very unlikely to be compromised.
         * The variability due to baseline power sector operation (typically 10%) is bounded by the variability levels examined in this analysis.  At all levels examined, the resulting variation in air quality is small.
         * Higher levels of emission variability (beyond what EPA has calculated here as year-to-year variability due to baseline operation of the power sector), such as could theoretically occur under an unlimited interstate cap-and-trade emission program, would not undermine the program's achievement of downwind air quality improvements.  This is especially true if coupled with emission reductions in the state containing the receptor.
         * The heterogeneity of where, when, and how emission reductions occur (processes not explicitly considered under the Transport Rule, such as intra-state shifting of emissions) will possibly have larger downwind air quality impacts at a given receptor than the minor variations in air quality attributable to the small shifts in state-level emissions due to inherent year-to-year variability.

      As was described in the proposed Transport Rule "Power Sector Variability" TSD, the variations in downwind air quality found in this analysis of potential year-to-year variability in upwind EGU emissions are much smaller than documented year-to-year variability in air quality (as measured at the receptors and expressed as the differences between the average and maximum design values), indicating that other factors such as meteorology play a much larger role in the variability of downwind air quality outcomes (once emissions are broadly controlled at a given level of stringency).  Consequently, EPA finds that allowing variation in emissions under the final variability limits in the Transport Rule allows the power sector to address inherent fluctuations in electric generation without negatively affecting downwind air quality.
      

