Exhibit 4  -  Senior I/M Program Details
Mobile6-based I/M emissions were retained for this off-model exercise because they were considered to still be conservatively high.  In the future, GA EPD and ARC will evaluate the development of MOVES-based senior I/M credits.
Effect of Senior Exemption on 2002 Highway Mobile Source Emissions
During their 1996 session the Georgia General Assembly amended the Georgia Motor Vehicle Emission Inspection and Maintenance Act (O.C.G.A. Section 12-9, et seq), to exempt from emission testing those otherwise subject vehicles ten years old or older driven fewer than 5,000 miles per year and owned by persons 65 years old or older. 
The actual numbers of vehicles that received senior citizen exemptions from Georgia's inspection and maintenance (I/M) program waiver centers in 2002 are shown in the table below (source: Appendix I, Detailed List of Waivers Processed, from 2002 Annual Operations Report for Georgia's Enhanced Inspection and Maintenance Program, July 30, 2003):
                   Table 1  -  Vehicles with Waivers by Year
                                  Age (years)
                                   Vehicles
                                      10
                                     1,629
                                      11
                                     2,120
                                      12
                                     2,239
                                      13
                                     2,630
                                      14
                                     2,496
                                      15
                                     2,350
                                      16
                                     2,369
                                      17
                                     2,227
                                      18
                                     1,708
                                      19
                                     1,111
                                      20
                                      669
                                      21
                                      586
                                      22
                                      496
                                      23
                                      833
                                      24
                                      794
                                      25
                                      44

2002 NOx Credit Loss 
MOBILE6.2 emission factors for calculating the 2002 NOx credit loss from these exempted vehicles were determined in the following manner. Six combined highway mobile source control strategies were modeled: 

   :: enhanced I/M in all 13 Atlanta ozone nonattainment area counties; 
   :: the Federal Motor Vehicle Control Program, including Tier 1 and Tier 2 tailpipe standards; 
   :: Stage II vapor recovery; 
   :: low-sulfur (150 parts per million, or ppm) and low Reid Vapor Pressure (7.0 pounds per square inch, or psi) gasoline; 
   :: the National Low Emission Vehicle (NLEV) program; and 
   :: technician training and certification). 

The enhanced I/M program is a decentralized annual hybrid with onboard diagnostics (OBD-II) system checks on 1996 and newer model year vehicles; and two-mode ASM tests on 25-year-old through 1995 model year vehicles. Anti-tampering inspections (checking for catalyst removal) are performed on 25-year-old through 1995 model year vehicles, and gas cap pressure tests are performed on all vehicles subject to inspection. 

   :: An overall 2002 highway mobile source NO inventory based on July 1, 2002, MOBILE6.2 emission factors with all controls in place (310,382,142 grams per day) was divided by the total summer-adjusted 2002 VMT (122,754,275 miles) with a resulting overall grams-per-mile NO emission factor of 2.528.
   :: MOBILE6.2 runs with all subject vehicles receiving their appropriate test were performed to determine the speed that would result in a July 1, 2002, NO emission factor of 2.528 grams per mile: 38.58 miles per hour.
   :: Two separate July 1, 2002, MOBILE6.2 runs, at 38.58 mph and with emissions calculated by model year, were made: one with hybrid I/M on 25-year-old and newer subject vehicles; the other with OBD-II system checks on 1996 and newer vehicles, with 1995 and older vehicles exempted. 
   :: Next, both sets (covered and exempt) of emission factors were separately multiplied by the VMT fractions, normalized to total 1.000, for the appropriate vehicle types (LDGV, LDGT12, LDGT34), and the three products were then added together to produce a single passenger vehicle emission factor for each exempted vehicle age. 
   :: The differences in the covered and exempt emission factors were then determined for each exempted vehicle age, these differences were multiplied by 4999, the maximum allowable yearly miles traveled by exempt vehicles, and that product was then multiplied by the number of vehicles of that age to determine grams per year.  Grams per year were converted to tons per day (907,180 grams per ton, 365 days per year) and the resulting NOx reduction credit loss for 2002 was determined to be 0.03 tons per day.
   
2002 VOC Credit Loss 
MOBILE6.2 emission factors for calculating the 2002 VOC credit loss from these exempted vehicles were determined in the following manner: 
   :: An overall 2002 highway mobile source VOC inventory based on July 1, 2002, MOBILE6.2 emission factors with all controls in place (158,026,372 grams per day) was divided by the total 2002 VMT (122,754,275 miles) with a resulting overall grams-per-mile VOC emission factor of 1.287. 
   :: MOBILE6.2 runs with all subject vehicles receiving their appropriate test were performed to determine the speed that would result in a July 1, 2002, VOC emission factor of 1.287 grams per mile: 30.6 miles per hour. 
   :: Two separate July 1, 2002, MOBILE6.2 runs, at 30.6 mph and with emissions calculated by model year, were made: one with hybrid I/M on 25-year-old and newer subject vehicles; the other with OBD-II system checks on 1996 and newer vehicles, with 1995 and older vehicles exempted. 
   :: Next, both sets (covered and exempt) of emission factors were separately multiplied by the VMT fractions, normalized to total 1.000, for the appropriate vehicle types (LDGV, LDGT12, LDGT34), and the three products were then added together to produce a single passenger vehicle emission factor for each exempted vehicle age. 
   :: The differences in the covered and exempt emission factors were then determined for each exempted vehicle age, these differences were multiplied by 4999, the maximum allowable yearly miles traveled by exempt vehicles, and that product was then multiplied by the number of vehicles of that age to determine grams per year. Grams per year were converted to tons per day (907,180 grams per ton, 365 days per year) and the resulting VOC reduction credit loss for 2002 was determined to be 0.05 tons per day. 
   
   
   
   

