## APPENDIX C

INVENTORY AND EMISSIONS MODELINGI. Methodology The emissions inventory model EMFAC2002, wh ich is used by the Air Resource Board (ARB) to estimate on-road motor vehicle em issions inventories, also calculates an inventory for urban buses. However, for a number of reasons staff believes that, without modification, the EMFAC model may not be suitable for developing regulations that address only urban transit buses. First, the population of the urban bus vehicle class in EMFAC is derived from the Departm ent of Motor Vehicles (DMV) registration database and contains urban buses as well as other categories of buses (examples are Greyhound and tour buses). The urban bus population reported by transit agencies is much smaller than the urban bus population in EMFAC. Second, the urban bus fleet in EMFAC contains 45 model years of vehicl es and buses of all ages are assumed to accrue 37,700 miles per year on average. Data reported for the years 2000-2002 by transit agency show that the transit bus fleetconsists of only 23 model years and that mileage accrual rate is a function of vehi cle age. Finally, the EMFAC model does not include alternative-fueled vehicles, but alternative-fueled buses have increasingly become an important part of every transit fleet. In support of the ARB’s amendments to the Fl eet Rule for Transit Agencies, staff has constructed an inventory model specifically for diesel and alternative-fueled urban buses. The model uses the population and activity data reported by transit agencies, diesel bus emission rates from the EMFA C model, and alternative-fueled bus emission rates estimated from recent test data. The following sections discuss the urban bus activity and emission rate estimates and present an urban bus specific inventory. II. Urban Bus Activity Data The Fleet Rule for Transit Agencies, adopted in 2000, has required that transit agencies provide an annual report of their urban buses since 2001. The population data were, therefore, based on reported data. The following urban transit bus acti vity data were obtained and analyzed:

• Annual mileage accrual rate;

• Population (POP) and age distribution;

• Total vehicle miles traveled (VMT). The annual mileage accrual rate for ur ban buses was estimated from the annual mileage data provided by transit agencies. The average annual mileage data by model year was statistically fit to obtain a re lationship between annual mileage accrual rate and vehicle age. Alternative-fueled urban bus es were assumed to accrue the same annual miles as diesel urban buses at the same age.C-2 A. Statewide The statewide population of urban buses, based on the 2002 reports from transit agencies, was 10,142, or 6,476 diesel buses and 3,666 alternative-fuel buses. Staff calculated the age distributions (number of vehicles by age) for diesel and alternativefueled urban buses using these data. For the statewide a lignment analysis, only the diesel population was analyzed. Alternativ e fuel urban buses are assumed not to be affected by engine availability as described below. Staff projected the population for future y ears for the statewi de baseline emissions, alignment scenario emissions , and statewide alternative fuel scenario based on the following assumptions:

• For the baseline scenario, no growth between 2004 and 2009 and growth resuming starting 2010 at a 1.6 percent growth rate. As stated, in the Staff Report, no engine manufacturer plans to certify a diesel engine for urban buses during this time frame. Therefore, st aff assumes that transit agencies on the diesel path will maintain their currentfleets through repow ering until 2010 when diesel engines become available. The slowdown in turnover is reflected in the reported data.

• For the alignment scenario, no growth between 2004 and 2006 and growth resuming starting in 2007 at a 1.6 percentgrowth rate. Diesel engines will be available at 1.2 g/bhp-hr NOx for 2007 through 2009. Fleets will start buying diesel buses again at their usual rate in 2007, however, once the 2010 diesel buses are available at 0.2 g/bhp-hr NO x, it is expected there will be larger purchases made in 2010 and 2011 to ca tch up to their needed fleet sizes.

• For the statewide alternative fuel mandat e, staff assumed the emissions would follow the same declining rate as was projected in the original rule since it followed the same engine standards path, i. e., 0.2 g/bhp-hr engines starting in 2007. However, the emissions starti ng points were adjusted to the 2006 emission values of 10.6 tons per day NOx and 420 pounds per day PM consistent with the baseline values. All purchases will be alternative fuel buses beginning in 2007 and continuing through 2015 when the alternative fuel path mandate expires, but all engines whether di esel or alternative fuel will meet the 0.2 g/bhp-hr NOx standard from 2010 on. Staff estimated the populations of diesel urban buses for 2003 and later model years using reported 2002 populations as the base year. The projected populations for future years were adjusted using the survival ra tes (the fraction of the new vehicles that remains in the fleet after certain years)for urban diesel buses in EMFAC2002 and modified to reflect the reported urban bus population survival rate. The urban bus daily vehicle miles traveled (V MT) for any given year was estimated from the population (POP) and accrual ra te using the following equation:
VMT = Σ (POP agex Accrual Rate i), where age= 0 to 22. (1)C-3 The urban bus mileage accrual rate, survival rate, and population distribution for years 2002 and 2020 are found in Table 1.
Table 1. Statewide Urban Bus Accrual Rate, Survival Rate and Population Distribution

Age Accrual Rate (mi/year) Survival Rate 2002 Diesel Population 1 2020 Diesel Population 2 0 30,868 1.00000 501 647 1 31,679 1.00000 675 658 2 32,332 1.00000 796 670 3 32,824 0.99301 364 657 4 33,158 0.99301 438 637 5 33,332 0.99301 558 615 6 33,346 0.98943 237 588 7 33,201 0.98774 215 556 8 32,897 0.98399 154 496 9 32,434 0.97909 165 466 10 31,811 0.93291 610 461 11 31,028 0.93291 360 444 12 30,087 0.84530 355 392 13 28,986 0.71960 398 344 14 27,725 0.60220 336 287 15 26,305 0.49520 7 250 16 24,726 0.37055 59 182 17 22,987 0.24590 41 120 18 21,089 0.13950 161 70 19 19,032 0.07180 20 48 20 16,815 0.02960 25 24 21 14,439 0.00070 0 0 22 11,904 0.00070 1 0 1 Reported by transit agencies. 2 Projected from year 2002 original rule population. B. South Coast Air Quality Ma nagement District (SCAQMD) The SCAQMD urban bus populat ion of 4,632 urban buses is based on data reported for 2004 by the 17 transit agencies located withi n the jurisdiction of SCAQMD, which reported populations of 1,865 diesel fuel and 2,767 alternative-fuel buses. Staff calculated the age distributions (number of vehicles by age) for diesel and alternativefueled urban buses using the survival rate s (the fraction of the new vehicles that remains in the fleet after certain years) based urban diesel buses in EMFAC2002. A 95C-4 percent fleet turnover rate of the oldest dies el buses to be replaced with alternative-fuel buses was used, except for years 2005 to 2009. For model years 2005 to 2009, staff conducted a telephone survey of the six diesel path transit agencies to obtain specific plans for purchasing, including replacement and growth vehicles (Table 2). All other assumptions regarding growth rate and VMT remain the same as in the statewide model . The population distribution for years 2005 and 2020 are given in Table 3.

Table 2. Reported Plans for Bus Purch ases, SCAQMD Diesel Path Agencies
Year GHEB 1 CNG Bus 2 2005 71 14 2006 23 2007 55 9 2008 64 2009 51 1 Gasoline Hybrid Electric Bus 2 Compressed Natural Gas BusC-5 Table 3. SCAQMD Transit Bus Population Distribution

Age 2005 Diesel Population 1 2020 Diesel Population 2 2005 Alt Fuel Population 1 2020 Alt Fuel Population 2 0 2 394 63 402 1 90 63 122 72 2 135 103 210 87 3 112 105 1054 134 4 233 138 322 75 5 24 42 321 68 6 42 78 266 70 7 255 92 359 70 8 99 106 1 72 9 127 75 17 52 10 48 76 32 247 11 25 2 6 12 387 88 6 13 19 131 7 14 59 110 7 15 68 228 7 16 101 22 59 17 0 39 114 18 9 238 197 19 0 92 982 20 0 116 296 21 0 44 294 22 30 22 242 1 Reported by transit bus agencies. 2 Projected from year 2005 population. III. Emission Rates of Diesel and Alternative-Fueled Urban Buses The diesel urban bus emission rates used for this analysis are the same as those used in EMFAC2002 version 2.2 (Table 4). T he emission rates are based on the currently adopted exhaust emission standards for urban bus engines and were adjusted for the modeled scenarios. Changes to the emission factors for the scenarios were calculated using a ratio between the adopted emissi on standard and the "projected" emission standard to determine the emi ssion rate for that year.C-6 Table 4. EMFAC2002 Diesel Ur ban Bus Emission Rates (g/mi) 1
Model Year Group HC NOx PM Pre 1987 2.06 46.18 1.29 1987-1990 2.05 40.20 1.22

1991-93 2.02 25.49 1.16 1994-95 1.99 29.84 1.41 1996-98 1.98 39.17 1.69 1999-02 1.98 20.39 0.58

2003 0.84 10.20 0.12 2004-06 0.84 2.55 0.12

2007 0.84 1.02 2,3 0.12 2008+ 0.75 0.90 2,3 0.10 1. Values assumed for baseline, if all engines were available. 2. The difference in the emission factors for 2007 and 2008+ is based on the implementation Zero Emission Bus purchasing requirements. 3 To model the alignment scenario, staff used emission factors of 6.14 for 2007 and 0.90 for 2010, to reflect certification values of 1.2 g/bhp-hr in 2007 and 0.2 g/bhp-hr (+ZEB) in 2010. Emission rates for alternative-fueled transitbuses were estimated from emission data collected by West Virginia University (WVU ) (Table 5). The WVU data include emission data for 71 1991-1998 model year CNG-powered urban buses. The emission data were first divided into model year groups corresponding to the model year groups of diesel transit buses and the data in each group were then averaged. Emission rates for model years after 1998 were estimated using the rati o of the standards. As with the statewide analysis, changes to the emission factors for the scenarios were calculated using a ratio between the adopted emission standard and t he "projected" emission standard to determine the emission rate for that year.C-7 Table 5. Alternative-Fuel Ur ban Buses Emission Rates (g/mi)
Model Year Group HC NOx PM 1991-93 14.6 25.4 0.02 1994-95 15.5 11.2 0.02 1996-98 20.7 20.0 0.02 1999-02 20.7 20.0 0.02

2003 7.96 10.0 0.004 2004-06 0.80 7.5 1 0.004

2007 0.80 1.0 0.004 2008+ 0.80 1.0 0.004 1 The range of the certification values for alternative-fuel buses is 0.6 to 2.5 g NOx+NMHC/bhp-hr. For the Baseline calculati on, staff used the average value of 1.5 g NOx/bhp-hr certification level to determine th e emission factor of 7.5 g/mi. For the scenarios, staff used the emission factor of 2.5g/mi (0.5 g/bhp-hr) because the predominant urban bus purchased in these years is the gasoline hybrid certified at the 0.6 g NOx+NMHC level. For comparison, Table 6 shows the currently adopted emission standards for urban buses. Table 6. Urban Bus Standards (g/bhp-hr)
Model Year HC CO NOX PM HC+NOx 1973-74 --- 40.0 --- --- 16.0 1975-76 --- 30.0 --- --- 10.0 1977-79 1.00 25.0 7.5 --- --- 1980-83 1.00 25.0 --- --- 6.0 1984-86 1.30 15.5 5.1 --- --- 1987-90 1.30 15.5 6.0 0.60 --- 1991-93 1.30 15.5 5.0 0.10 --- 1994-95 1.30 15.5 5.0 0.07 --- 1996-98 1.30 15.5 4.0 0.05 --- 1999-02 1.30 15.5 4.0 0.05 --- 10/2002-03 --- 15.5 2.5 (NOx+NMHC) 0.01 ---

2004-06 15.5 Diesel: 0.5 Alt Fuel:2.5 (NOx+NMHC) 0.01 --- 2007 15.5 0.2 0.01 ---
2008+ 15% of new purchases are ZEBs for large fleetsC-8 IV. Urban Bus Emission Inventory Using the data presented above, staff calculat ed baseline inventorie s for the statewide and SCAQMD urban buses. Tables 7 and 8 show the diesel urban bus baseline inventories for selected calendar years fo r the statewide and SCAQMD inventories and Tables 9 presents the alternative-fueled urban buses for the SCAQMD inventories. Table 7. Statewide Diesel Urban Bu s Baseline Emissions (tons/day)

Pollutant 2000 2005 2010 2015 2020 HC 0.56 0.52 0.41 0.25 0.09 NOx 13.5 10.6 7.93 3.72 1.37 PM (lbs/day) 540 420 320 142 100 Table 8. Statewide Alignment Scenario Emissions (tons/day)

Pollutant 2000 2005 2010 2015 2020 HC 0.56 0.52 0.39 0.26 0.10 NOx 13.5 10.6 7.79 4.91 1.86 PM (lbs/day) 540 420 300 142 100
Table 9. Statewide Alternative Fue l Path Mandate Scenario Emissions (tons/day)

Pollutant 2000 2005 2010 2015 2020 HC 0.56 0.52 0.55 0.56 0.56 NOx 13.5 10.6 7.18 3.72 1.37 PM (lbs/day) 540 420 300 142 100
Table 10. SCAQMD Diesel Urban Bu s Baseline Emissions (tons/day)

Pollutant 2000 2005 2010 2015 2020 HC 0.23 0.15 0.13 0.11 0.062 NOx 5.72 3.03 2.64 2.11 1.19 PM (lbs/day) 239 125 107 85.3 48.8C-9 Table 11. SCAQMD Alternative- Fuel Urban Bus Baseline Emissions (tons/day)

Pollutant 2000 2005 2010 2015 2020 HC 2.61 5.42 5.19 4.17 2.38 NOx 2.50 5.27 5.06 4.09 2.38 PM (lbs/day) 5.1 10.5 10.3 8.6 5.6