

                               January 10, 2022

--------------------------------------------------------------------------------
 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
--------------------------------------------------------------------------------
REGION 8
--------------------------------------------------------------------------------
1595 Wynkoop Street
--------------------------------------------------------------------------------
DENVER, CO   80202-1129
--------------------------------------------------------------------------------
Phone 800-227-8917
--------------------------------------------------------------------------------
http://www.epa.gov/region08
--------------------------------------------------------------------------------
0
Ref: 8P-AR

MEMORANDUM							

SUBJECT: 	Thompson Falls, MT Motor Vehicle Regional Emissions Analysis

FROM:	Kate Gregory
		Region 8, EPA
		Air Quality Planning Branch
		

TO: 		File					

According to the Limited Maintenance Plan (LMP) Option for Moderate PM10 Nonattainment Areas (NAA) memo, in order to qualify for the LMP option, "The final criterion is related to mobile source emissions. The area should expect only limited growth in on-road motor vehicle PM10 emissions (including fugitive dust) and should have passed a motor vehicle regional emissions analysis test. It is important to consider the impact of future transportation growth in the LMP, since the level of PM-10 emissions (especially from fugitive dust) is related to the level of growth in vehicle miles traveled (VMT).

The following methodology can be found in Attachment B of the LMP Option memo, and is used to determine whether increased emissions from on-road mobile sources could, in the next 10 years, increase concentrations in the area and threaten the assumption of maintenance that underlies the LMP policy.  

The equation set forth is:
                         DV + (VMTpi * DVmv) <=  MOS
Where:
      DV = design concentration in ug/m[3] 
      VMTpi = projected increase in vehicle miles traveled (VMT) over the next 10 years
      DVmv = product of the design value and the fraction of the inventory represented by on-road mobile sources in the attainment year; and
      MOS = margin of safety for the relevant PM10 standard for a given area: Prescriptive value of 98 ug/m[3] for the 24-hour standard.


Thompson Falls Vehicle Regional Emissions Analysis Calculation:
Utilizing a design concentration of 75 ug/m[3]; a projected 25.41% VMT increase; and a 0.1903 fraction of the inventory represented by on-road mobile sources in the attainment year the results are as follows:

         75 ug/m[3] + (0.2541 * (75 ug/m[3])(0.1903)) =  79 ug/m[3]
                                       
                         79 ug/m[3] < 98 ug/m[3] 

Based on the above methodology, as outlined in the LMP option memo, the projected 25.41% VMT increase does not indicate that increased emissions from on-road mobile source should in the Thompson Falls PM10 NAA, in the next 10 years, increase concentrations in the area and threaten the assumption of maintenance.



