# Appendix C

Mobile Source Emissions Modeling
for Atlanta Ozone Reasonable Further Progress State Implementation PlanMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-1 

## Overview

The Georgia Environmental Protection Divisi on (EPD) worked with the Atlanta Regional Commission (ARC) to develop mobile 1 source emissions inventories for the purpose of establishing motor vehicle emission budgets (MVEB) for the Atlanta 8-Hour Ozone Reasonable Further Progress (RFP) State Impl ementation Plan (SIP) revision, hereinafter
called the Ozone RFP Plan. These invent ories reflect the most recent planning assumptions and emission factor model 2 available, and the use of updated travel demand
and emissions calculation models. The AR C's travel demand and emissions estimation modeling process was employed to estimate on-road mobile source emissions. The
mobile source emission inventories for the Oz one RFP Plan MVEB were calculated in a manner consistent with federal regulations for performing regional emissions analyses used in transportation conformity determin ations. The alignment of methodologies for mobile source inventories and transportation conformity emissions analyses prevents spurious differences between motor vehicle emission budgets (i.e., the SIP's estimate of future mobile source emissions) and transpor tation conformity analyses that must conform to those budgets.

The 20-county Atlanta ozone nonattainment area wa s originally classified as a "marginal" nonattainment area. With an attainment ye ar of 2007, marginal 8-hour ozone areas were required to attain the National Ambient Air Quality Standards (NAAQS) by the 2006 ozone season. Because monitoring data from the 2006 ozone season indicated that
Atlanta had not attained the NAAQS, the area was reclassified 3 to "moderate." In ozone nonattainment areas with air quali ty classified as moderate or worse, a reasonable further progress demonstration, pe r Section 182(b) of the Cl ean Air Act (CAA), requires emission reductions equaling 15% within six y ears of the base year (i.e., by the end of 2008 for the 8-hour ozone NAAQS).

The initial 15% reduction must be in emissions of volatile organic compounds (VOC). Per 40 CFR Part 51.910(a)(1)(iii), Require ments for Preparation, Adoption, and Submittal of Implementation Plans, moderate areas of which a portion has an approved 1-
hour ozone 15% VOC Plan can choose to trea t the nonattainment area as two parts, each with a separate RFP target, and may substitu te reductions in nitrogen oxides (NOx) for VOC in the sub-area with the approved 15% Plan. The 15% reduction for the sub-area without an approved 15% VOC Plan must sti ll be entirely VOC. Because photochemical air quality modeling indicates that NOx reductions are more effective than VOC reductions in reducing ozone c oncentrations in the region, 4 Georgia has chosen to rely solely on NOx emission reductions in the 13-county part of the Atlanta ozone
nonattainment area with an approved 15% VOC Plan.

1 The term "mobile" is used to describe emissions from on-road motor vehicles.

2 MOBILE6.2.03 ( http ://www.epa.gov/otaq/m6.htm#m60 )

3 73 Federal Register 12013, March 6, 2008

4 See Appendix A, Sensitivity of ozone concentrations in Atlanta to NOx and VOC controls inside and
outside the nonattainment area ( http ://www.gaepd.org/Files_PDF/plans/sip/app_a_nox _substitution_and_out _of_area_benefits.pdf )Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-2 For use in making transportation conformity determinations for the Atlanta 8-hour ozone nonattainment area, the Ozone RFP Plan w ill establish MVEB for the year 2008. In contrast with previous EPA guidance and with Georgia’s approve d Post-1996 9% Plan
and Post-1999 ROP 5 Plan, this Ozone RFP Plan does not rely on any emission reductions
outside the nonattainment area. As determ ined through interagency consultation, the
emission factors used reflect an assumption that ethanol-blend gasoline had 100 percent market share in summer 2008. Modeling assump tions were distributed to the interagency consultation partners on October 28, 2008.



## Mobile Source Emissions Inventory

In order to develop the Ozone RFP Plan MVEB, 2002 Base Year and 2008 budget year
VOC and NOx emission inventories for th e 20-county eight-hour ozone nonattainment area were produced. Reference Figure C-1 for a map of the nonattainment area. The Base Year inventories were adjusted by removing VOC and NOx already scheduled for control by previous federal regulations on motor vehicles and gasoline volatility as required by Section 182(b)(1) of the CAA.

According to the EPA's MOBILE6 policy guidance, 6 "If SIPs are revised..., base year...motor vehicle emission inventories will need to be recalculated with the latest available planning assumptions... Base year... inventories should use the best data available for those years." The motor vehi cle emissions inventories for years 2002 and 2008 for the 20 counties that comprise the 8- hour ozone nonattainment area reflect the
latest travel demand and emissions mode ling processes used for transportation conformity purposes by the ARC, and late st available planning assumptions as documented in Appendix C, Exhibits 3 and 4.

5 The terminology EPA uses for progress towards attainment has been codified at 40 CFR Part 51.900: "reasonable further progress" (RFP) is used for the 8-hour ozone NAAQS, "rate of progress" (ROP) is used for the former 1-hour NAAQS.

6 http ://www.epa.gov/otaq/models/mobile6/m6policy.pdf

### Figure C-1
Atlanta Ozone Nonattainment Area

Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-3Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-4 

## Emissions Inventory - 20 County Eight-Hour Ozone
Nonattainment Area

In support of Ozone RFP Plan MVEB development, the ARC produced nonattainment
area mobile emissions inventories for the 2002 Base Year, the 2002 Adjusted Base Year, and the 2008 RFP budget year. The travel demand and emissions modeling process and the planning assumptions used for the Ozone RFP Plan are summarized below and in Appendix C, Exhibits 3 and 4.

The ARC currently maintains a travel model for 20 counties that co rrespond to the eighthour ozone nonattainment area. The ARC tr avel demand model is designed to, at minimum, represent the state of the practice in travel demand modeling and to meet all modeling requirements specified in the federa l Transportation Conformity Rule (40 CFR Parts 51 and 93). The Transportation Conformity Rule establishes a regulatory requirement that includes minimum specificati ons for travel models used to forecast vehicle activity for regional emission analys es in certain nonattainment and maintenance areas. These minimum specifications (see 40 CFR Section 93.122(b)) apply to metropolitan planning areas with an urbani zed area population over 200,000 that are also serious, severe, or extreme ozone; or se rious carbon monoxide; nonattainment areas.
Atlanta met those conditions under the one- hour ozone standard, for which the area had been classified as serious (effective Janua ry 6, 1992) and severe (effective January 1, 2004), before being redesignated to attainment of the one-hour ozone standard (effective June 14, 2005). Because travel model VMT are adjusted to count-based estimates before being used for emissions calculations, the bi ggest remaining difference between networkmodel-based activity and activity estimated using other "appropriate methods [40 CFR Section 93.122(d)]" is the level of speed averaging. Despite th e fact that Atlanta's current ozone nonattainment classification (moderate) would not otherwise subject it to the modeling requirements of 93.122(b), EPA regulations 7 require the continued use of activity from network-based tr avel models for transportation conformity emissions estimates in Georgia.

A full consultation process, including national peer review, and the ARC strategic travel demand model enhancement program guide all m odifications to the travel demand model. As a result, all elements of the travel dema nd model are designed to support all technical and policy decisions that are required in developing a comprehensive, multimodal transportation plan and program in accordan ce with the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), the 1990 Clean Air Act Amendments, and the Transportation Conformity Rule.

The previously most recent emissions inve ntories developed usi ng ARC’s travel demand and emissions modeling process were completed as part of the transportation conformity

7 "In all areas not otherwise subject to paragraph (b) of this section, regional emissions analyses must use those procedures described in paragraph (b) of this section if the use of those procedures has been the previous practice of the MPO [40 CFR Section 93.122(d)]."Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-5 analysis for ARC's Envision6 2030 Regional Tr ansportation Plan (RTP) and associated FY 2008-2013 Transportation Improvement Program (TIP); and the Gainesville-Hall MPO's 2030 RTP and associated 2008-2013 TIP; approved by the U.S. Department of Transportation (USDOT), in consultation wi th the EPA, on October 10, 2007. A number of enhancements to the travel demand model, described below, ar e reflected in those
inventories and in the inventories devel oped for the Ozone RFP Plan MVEB. Some changes to the travel model were a result of a significant model recalibration initiated after the expansion of the modeling platform from a 13-county to a 20-county geography. Enhancements include updated population and employment estimates that reflect the expanded modeling platform, as well as struct ural changes within the model needed to recalibrate to its base ye ar, 2000, including the following:

• Mode choice model updated to improve pe rformance of suburban intra-county trips,

• Attraction share model incorporated in to four-step modeling process, and

• New commercial vehicle and truck model developed to improve traffic assignment for both passenger vehicl es and truck traffic.

The ARC’s emissions model has also been updated to reflect all travel model improvements resulting from expansion to the 20-county geography and subsequent 2000 base year recalibration. The emissions modeli ng procedure requires input of travel model networks for the specific scenario years, in this case 2002 and 2008. External files that specify VMT adjustment factors and MOBI LE6 emission factors are also required. Changes to these networks and exte rnal files include the following:

• Network files reflect expansion of model system to cover the 20-county eight-hour ozone nonattainment area (2002 and 2008 travel model network years),

• Highway Performance Monitoring System (HPMS) adjustment factors 8 updated to
reflect the latest 20-c ounty travel model recal ibration for year 2000,

• Updated seasonal adjustment factors, and

• Latest MOBILE6 emission factors.

Travel Model Networks To prepare the mobile source emissions inve ntories for establishing the Ozone RFP Plan MVEB, it was necessary to create a 2002 tran sportation network that accurately reflected the transportation system in place during the 2002 base year, as well as a transportation network for 2008. The year 2002 network needed for the baseline inventory was derived from the base year 2000 travel model networ k; no regionally signi ficant projects were opened to traffic between 2000 and 2002. Year 2002 population and employment data was interpolated from the latest regional control demographic forecasts documented in Appendix C, Exhibit 4 ( http ://www.gaepd.org/Files_PDF/plans/sip/ exhibit_4_PopEmp_PlanAssumptions_0422 08.pdf ).

8 The VMT from the travel demand model are adjust ed based on the VMT estimates that Georgia DOT develops for HPMS.Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-6 The year 2008 network needed for the 2008 RFP MVEB inventories was derived from
the 2010 travel model network. Year 2008 population and employment data were interpolated from the latest regional c ontrol demographic forecasts documented in Appendix C, Exhibit 4.

A small portion of the Atlanta Urbanized Ar ea extends into Hall County. In February 2003, the Gainesville-Hall MPO (GHMPO) was de signated for the Gainesville Urbanized Area; the planning boundary for the GHMPO covers Hall County in its entirety. Hall County is included in Atlanta's ozone nonattainment area. The ARC, by agreement with the GHMPO, performs the emissions modeling for Hall County. Travel model networks reflect the project listing as approved:

• in ARC's Envision6 2030 RTP and 2008- 2013 TIP; adopted by the ARC Board September 26, 2007; and received a positive conformity determination from USDOT October 10, 2007; and

• in the GHMPO's 2030 RTP and 2008-2013 TIP; adopted by the GHMPO Board August 14, 2007; and received a positive c onformity determination from USDOT October 10, 2007

Project coding for network years 2002 (bas ed on 2000 network) and 2008 (based on 2010 network) was reviewed by state and local project sponsors in March and April 2007 as part of the development of the Envision6 and GHMPO 2030 RTPs and FY 2008-2013
TIPs. Year 2002 and 2008 networks were r un through a full travel model assignment procedure, based on the recal ibrated model stream, to pr oduce the VMT and speeds for the respective mobile sour ce emission inventories.

VMT Adjustment Factors Traffic volumes produced by the travel model are adjusted within the emissions modeling process by applying a VMT adjustment f actor, which is a combination of HPMS adjustment factors, used to reconcile travel model VMT to HPMS VMT estimates, 9 and seasonal adjustment factors used to convert the average annual daily traffic produced by the travel model to average summer-time daily traffic for the purposes of ozone precursor emissions modeling. 10

EPA requires 11 that reasonable methods be used to estimate VMT on off-network (offmodel) roadways within the urban transporta tion planning area. Off- model VMT is travel that is accounted for within HPMS estimates, but not accounted for within the coded transportation network; it typically reflects tr avel on the local road system. EPA also recommends, 12 for areas with travel demand models in place, that HPMS adjustments be

9 40 CFR Sections 93.122(a)(7) and 93.122(b)(3)

10 Section 3.4.2.6 Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources , EPA420-R92-009, USEPA Office of Air and Radiation, Office of Mobile Sources, 1992.

11 40 CFR Section 93.122(a)(7)

12 40 CFR Section 93.122(b)(3)Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-7 made based on comparison of base year VMT fr om the transportation model to base year
HPMS VMT estimates. The ARC calculates HPMS adjustment factors by comparing HPMS VMT to travel model VMT by 12 HPMS functional classes for the 2000 calibration year. The resulting factors are then applied to travel model VMT estimates for future analysis years. The following equation was used to calculate the HPMS adjustment factors:

HPMS Adjustment Factor i = 2000 HPMS VMT i / 2000 MODEL VMT i (where i=HPMS functional class)

To determine the "2000 HPMS VMT," aver age daily VMT for the year 2000 were grouped by the 12 HPMS functional classes for the 13 counties 13 that correspond to the nonattainment area for the previous 1-hour oz one standard where a 15% VOC Plan is in place, and, separately, for the 7 counties 14 that were not part of the 1-hour ozone nonattainment area, but are nonattainment unde r the 8-hour ozone st andard, where there is not currently a 15% VOC Plan. County- level HPMS data by functional class was taken from the Georgia Department of Transportation's (Georgia DOT) Office of Transportation Data "445 Report." Georgi a DOT's 445 Report provides information on mileage and VMT by route type and road sy stem and contains county-specific State Route, County Road and City Street mileage and VMT broken down by functional classification. VMT by county and functional class were aggregated to total VMT by
HPMS functional class. "2000 Travel Dema nd Model VMT" at the HPMS functional
class level was derived from the recalibr ated 2000 travel model network. HPMS adjustment factors for the 13- and 7- county areas are listed below.

Note that for the HPMS adjustment factors for the 7-county area, urban and rural HPMS VMT were combined by HPMS functional clas sification prior to comparing with ARC
travel model VMT. Travel model network coding for the 7-count y area took place in early 2006 and reflects the latest version (f rom the 2000 Census) of the urbanized area
definition. The 2000 HPMS data that is used as the base for calculati on of the adjustment
factors reflects the 1990 Census urbanized area definition. Georgia DOT did not update
to the 2000 Census definitions until calenda r year 2005, with their 2004 445 Report. In
order to avoid a disconnect between travel model VMT in the 7 c ounties coded with 2000 Census urban/rural designa tions and 2000 HPMS VMT that reflects the 1990 definition, the urban and rural VMT were combined by functional class before the factors were calculated. This produced four unique HPMS ad justment factors for the 7-county area, as opposed to 12 unique factors calculated for the 13-county area.

13 (Cherokee, Clayton, Cobb, Coweta, DeKalb, Douglas, Fayette, Forsyth, Fulton, Gwinnett, Henry, Paulding, and Rockdale)

14 (Barrow, Bartow, Carroll, Hall, Newton, Spalding, and Walton)Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-8 

### Table C-1 HPMS Adjustment Factors – 13 Counties

Functional Class
Name Functional Class
Number HPMS VMT Model VMT Factor
Rural Interstate 1 5,470,815 8,583,156 0.64 Rural Principal Arterial 2 3,578,882 3,579,075 1.00

Rural Minor Arterial 6 3,821,128 3,343,871 1.14 Rural Major Collector 7 3,510,608 4,021,609 0.87
Rural Minor Collector 8 1,191,162 1,121,165 1.06
Rural Local 9 3,322,148 5,199,188 0.64
Urban Interstate 11 35,934,531 35,043,828 1.03 Urban Other Freeway 12 5,765,979 2,422,195 2.38 Urban Principal Arterial 14 10,398,680 15,341,281 0.68

Urban Minor Arterial 16 22,101,606 18,118,598 1.22
Urbanized Collector 17 7,540,916 6,098,164 1.24

Urbanized Local 19 15,412,042 15,841,739 0.97



### Table C-2 HPMS Adjustment Factors – 7 Counties

Functional Class
Name Functional Class
Number HPMS VMT Model VMT Factor
Rural Interstate 1 4,160,787 2,426,269 0.85 Rural Principal Arterial 2 3,912,496 1,299,608 0.97

Rural Minor Arterial 6 3,843,626 1,784,578 0.97 Rural Major Collector 7 2,498,042 1,435,602 1.80
Rural Minor Collector 8 1,019,255 303,600 1.80
Rural Local 9 3,112,673 1,515,043 1.09
Urban Interstate 11 322,200 2,510,593 0.85 Urban Other Freeway 12 0 310,430 0.85 Urban Principal Arterial 14 2,874 1,979,977 0.97

Urban Minor Arterial 16 17,640 2,952,583 0.97
Urbanized Collector 17 0 216,380 1.80

Urbanized Local 19 20,796 1,353,590 1.09

Summer (seasonal) adjustment factors are used to convert from average annual daily VMT to average summer-season daily VM T for the purposes of ozone precursor emissions modeling. 15 Seasonal adjustment factors we re the latest factors provided by the Georgia DOT Office of Transportation Data, on August 9, 2006. Summer-adjustment
factors for the 13- and 7- count y geographies are listed below.

15 Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources , Section 3.4.2.6, EPA420- R-92-009, USEPA Office of Air and Radiation, Office of Mobile Sources, 1992.Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-9 

### Table C-3 Summer Adjustment Factors

Functional Class Name 13-Co unty Factor 7-County Factor
Rural Interstate 1.05 1.04 Rural Principal Arterial 1.02 1.02

Rural Minor Arterial 1.01 1.01 Rural Major Collector 1.00 1.00
Rural Minor Collector 1.01 1.01
Rural Local 1.01 1.01
Urban Interstate 1.02 1.00 Urban Other Freeway 1.03 1.00 Urban Principal Arterial 0.99 1.00

Urban Minor Arterial 0.99 0.99
Urbanized Collector 0.97 1.00

Urbanized Local 0.97 0.97

HPMS adjustment factors were multiplied by the seasonal adjustment factors for each HPMS functional classification to produce a set of VMT adjustment factors by HPMS functional classification for 13-county a nd 7-county portions of the 20-county nonattainment area, separately. VMT ad justment factors are listed below.



### Table C-4 VMT Adjustment Factors

Functional Class Name 13-Co unty Factor 7-County Factor
Rural Interstate 0.67 0.89 Rural Principal Arterial 1.02 0.99

Rural Minor Arterial 1.16 0.98 Rural Major Collector 0.88 1.81
Rural Minor Collector 1.07 1.81
Rural Local 0.64 1.10
Urban Interstate 1.05 0.86 Urban Other Freeway 2.44 0.85 Urban Principal Arterial 0.67 0.97

Urban Minor Arterial 1.21 0.96
Urbanized Collector 1.21 1.80

Urbanized Local 0.95 1.06

MOBILE6 Emission Factors Emission factors were produced for 2.5 mile s per hour (mph), then 3 mph to 65 mph, inclusive, in one mile per hour incr ements for VOC and NOx using EPA's
MOBILE6.2.03 model. Mobile source emissi ons are calculated by multiplying the VMTMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-10 for each link 16 in the travel model network by th e corresponding VMT adjustment factor (by HPMS class), then by an emission factor that corresponds to the congested flow speed of the link. Link level emissions are then summed to the time of day, and daily level, for reporting purposes.

Emission factors reflect two types of programs, the federally mandated motor vehicle emission control programs and the locally specific parameters for Atlanta.

Federal Programs Regional Parameters
National Low Emission Vehicle Sta ndards Average Fuel Volatility Heavy-Duty Vehicle Emission Standards Vehicle Registration Information
Tier 1 Emission Standards Ambient Weather Conditions
Tier 2 Emission Standards 17 Inspection & Maintenance Program Low-Sulfur Georgia Gasoline 18

MOBILE6 estimates emissions for four types of "driving cycle" - arterial/collector, freeway, ramp, and local road. It is assumed that all VMT by motor vehicles will occur in one of these four driving cycles. Each driving cycle implies different assumptions about vehicle activity and diffe rent emission estimates in MOBILE6. The definitions of the different driving cycles from EPA's Technical Guidance on the Use of MOBILE6.2 for Emission Inventory Preparation 19 are given below.

• Freeway Driving Cycle

In MOBILE6, "freeway" VMT refers to driving that occurs on roadways that do not have traffic signals, that usually have limited access (via converging ramps) and have free flow speeds greater than 50 miles per hour. Thes e roadways are usually divided and have
more than one lane in each direction. This definition does not include short sections (less than two miles) of a roadway between si gnals, but could include longer roadway segments that effectively act as freeways.

• Arterial/Collector Driving Cycle

In MOBILE6, "arterial/collector" VMT refers to driving that occurs on roadways that have signalized traffic control. These road ways are not freeways, because they have traffic signals, but they may be divided, multip le lanes, one-way and have high free-flow speeds. However, traffic will be stopped periodically by traffic signals and will be

16 A link refers to a section of the modeled road networ k in which none of the describing attributes change (e.g., link "A" is a segment of a highway that has 4 lanes with speed limit of 55; if the number of lanes changes, then a new link should be coded).

17 (beginning with 2004 models)

18 when different from federal sulfur levels

19 http ://www.epa.gov/otaq/models/mobile6/420r04013.pdfMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-11 further affected by access to the roadway by driveways and un-signalized intersections. Even in free flow, the driving on arteria l/collector roadways will be characterized by cruising periods interrupted by traffic signals.

• Local Roadway Driving Cycle

In MOBILE6, "local roadway" VMT refers to driving on roadways that are not normally considered as part of the tr affic network. These roadways do not have traffic lights and rarely have more than one lane in each di rection. They usually allow vehicle parking on the roadway surface and traffic control is handled via stop/yield signs. Speed limits are normally 30 miles per hour or less. The dr iving cycle used in MOBILE6 to model local roadways is fixed at an average speed of 12.9 miles per hour. Driving on local roadways is characterized by extremely low speeds a nd frequent stops at intersections.

• Freeway Ramp

In MOBILE6, "freeway ramp" VMT refers to the access roadways for freeways. It includes both traffic entering the freeway and exiting. Driving on freeway ramps is characterized by rapid acceler ation from stop or low speeds to freeway speeds and decelerations from freeway speeds to low spee ds or stop. Freeway ramp activity is not included in the MOBILE6 freeway roadway defi nition. Therefore, a ll freeway activity must include a corresponding freeway ramp activity to account for acceleration and deceleration to and from freeway speeds.

Many areas do not explicitly account for freew ay ramps as a separate roadway type so EPA developed a default ramp fraction (8% of freeway travel) for MOBILE6 users to account for this. This approach is not necessary for Atlanta's nonattainment area freeway emission estimates because freeway ramps have been explicitly defined in the ARC highway network. Freeway ramps have been defi ned as separate facilities stratified by the type of design and speed, high, medium and lo w. High-speed ramps represent ramps that connect freeway-to-freeway travel, such as I-285 to I-85N, while the lower speed ramps are for access to a freeway from an arterial or egress from a freeway to an arterial. The high-speed ramps in the ARC model have signi ficantly higher free-flow speeds than the lower speed ramps and are not characterized by rapid acceleration or by deceleration from freeway speeds to low speeds or stops. Based on guidance from EPA, emissions for high-speed freeway ramps are estimated using non-ramp freeway emission factors while emissions for lower speed freeway ramps are estimated using freeway ramp
emission factors.

In MOBILE6, only arterial/collector and freew ay emissions are speed sensitive. Emission factors were produced for 2.5 miles per hour and, in one mile per hour increments, between 3 mph and 65 mph, inclusive, for th ese two driving cycles. The all-vehicles composite emission factors were used to deve lop the mobile source emissions inventories
for the MVEB.Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-12 Emission factors are applied to travel model VMT based on the appropriate driving cycle and congested flow speed. The mapping of MOBILE6 roadway type to both HPMS functional class and ARC roadway facility type 20 used for the MVEB emissions modeling is shown in Tables C-5 and C-6, below. The appropriate MOBILE6 roadway type can be determined by us ing the facility type defini tions in the highway network except for the rural other principal arterial. EPA believes that facilities with the HPMS classification of rural other principal arteri al should be modeled us ing a combination of the freeway and ramp emission factors. EPA has recommended that the freeway emission factors be applied to 92% of the VMT while the ramp emission factors be applied for the remaining 8% of the VMT for th ese facilities. This is the only case where a combination of emission factors by drivi ng cycle is used for the same functional classification. In the ARC highway networks, f acilities with rural other principal arterial
HPMS classifications have diffe rent facility types, ranging from expressway to different types of arterials. Within the ARC emissi ons modeling procedure, the HPMS functional classification, facility type, and free-flow speed for each link are checked to determine the appropriate MOBILE6 driving cycle for this category. Only links with a facility type of arterial or collector, an HP MS classification of rural other principal arterial, and a freeflow speed greater than 50 mph, will have the VMT adjusted based on the above criteria. Facilities with a freeway facili ty type and an HPMS classifi cation of rural other principal arterial will not be adjusted. Table C-5 lis ts the mapping of HPMS functional classes to MOBILE6 driving cycles and Table C-6 lists the mapping of the ARC facility types to the MOBILE6 driving cycles.

20 ARC uses a more refined breakdown of roadway types for travel demand modeling to enable a more accurate estimate of roadway volume s and speeds. ARC roadway types ar e referred to as Facility Types.Mobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-13 

### Table C-5
HPMS Functional Classifications Mapped to MOBILE6 Driving Cycles

HPMS Highway Functional Syst em MOBILE6 Driving Cycle
Rural interstate Freeway and freeway ramp Rural other principal arterial Freeway and freeway ramp
Rural minor arterial Arterial/collector Rural major collector Arterial/collector
Rural minor collector Arterial/collector
Rural local Local
Urban interstate Freeway and freeway ramp Urban other freeways Freeway and freeway ramp Urban other principal arte rial Arterial/collector
Urban minor arterial Arterial/collector
Urban collector Arterial/collector
Urban local LocalMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-14 

### Table C-6 Listing of ARC Facility Type Classifications by MOBILE 6 Driving Cycles Facility Type Classification Code Area Type MOBILE6 Driving Cycle Interstate/Freeways 1 Urban/Rural Freeway Parkway 2 Urban/Rural Freeway HOV Buffer Separated 3 Urban/Rural Freeway HOV Barrier Separated High Speed Ramps/CD
Roads 4
5 Urban/Rural
Urban/Rural Freeway Freeway

Principal Arterial – Class I* 12 Ru ral Arterial/collector or Freeway and Ramp Principal Arterial – Class I 12 Urban Arterial/collector Principal Arterial – Class II* 13 Ru ral Arterial/collector or Freeway and Ramp Principal Arterial – Class II 13 Urban Arterial/collector
Minor Arterials – Class I 14 Rural Arterial/collector
Minor Arterials – Class I 14 Urban Arterial/collector
Minor Arterials – Class II 15 Rural Arterial/collector
HOV Arterials 16 Urban/Rural Arterial/collector Major Collector 17 Urban/Rural Arterial/collector
Minor Collector 18 Urban/Ru ral Arterial/collector Medium Speed Ramp 6 Urban/Rural Ramp Low Speed Ramp 7 Urban/Rural Ramp Loop Ramp 8 Urban/Rural Ramp Off Ramp w/Intersectio n 9 Urban/Rural Ramp On Ramp w/Intersection 10 Urban/Rural Ramp Planned Ramps
w/Intersections 19 Urban/Rural Ramp

Planned Directional Ramps 20 Urban/Rural Ramp
Centroid Connectors 0 Urban/Rural Local *If HPMS classification is Rural Other Principal Arterial and free-flow speed is >50 mph - 92% of VMT allocated to freeway while 8% allocated to ramp

Specific variables within the MOBILE6 inputs for the MVEB inventories are
documented below.

• Ambient Weather Conditions MOBILE6 allows relative humidity and temperat ure to be input for each hour of the day, with a single entry for barome tric pressure. Hourly humidity and temperature inputs, and daily barometric pressure, were derive d from National Weather Service Local Climatological Data from the 10 days with th e highest ozone concentrations for the threeyear period 2000-2002. The hourly humidities a nd temperatures were averaged acrossMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-15 the 10 days. The daily average barometric pres sures for the 10 days were also averaged.
See Exhibit 1 for details. 21

• Fleet Age Separate, area-specific regist ration distributions by age for the 13- and 7-county parts of the Atlanta ozone nonattainment area, develope d using registration data obtained from R.L. Polk & Company, 22 were modeled. In keeping with EPA guidance, 23 the
MOBILE6 default distribution was used for th e heaviest (Class 8B) heavy-duty vehicles.

• Gasoline 24 The 2002 Base Year and the 2008 RFP budget year mobile source emissions inventories
for the Atlanta 8-hour ozone nonattainment area reflect the effects of the low-sulfur and low RVP gasoline required by state rule in a nd near the nonattainment area. In 2002, sulfur and RVP were 150 parts per milli on average and 7.0 pounds per square inch, respectively. For the 2008 RFP budget year, Phase 2 Georgia Gas (30 ppm sulfur, 7.0 psi RVP) with 100% market share ethanol ble nd (10% by volume) and an RVP waiver was assumed. Per Georgia's Gasoline Marketing Rule, 391-3-1-.02(2)(bbb), this waiver allows the RVP of ethanol blend gasolin e to rise as high as 8.0 psi.

• Vehicle Inspection and Maintenance Program The vehicle inspection and ma intenance (I/M) program in place in 1990 was modeled for the nonattainment area Adjusted Base Year mobile source inventory. This was a decentralized program for 12-years-old-and-ne wer cars and light trucks in Cobb, DeKalb, Fulton, and Gwinnett counties. That annual progra m consisted of an idle test and a check for tampering of three items: air pump sy stem, catalytic converter, and fuel inlet
restrictor. For 2002 Base Year and 2 008 mobile source emissions modeling, the enhanced I/M program 25 in place in the 13-county part of the nonattainment area was modeled. This annual program requires onboa rd diagnostics system checks on 1996 and newer model year cars and light trucks, 2- mode ASM tests on 25-year-old through 1995

21 http ://www.gaepd.org/Files_PD F/plans/sip/exhibit_1_h ourly_temp_and_humidity.pdf

22 Registration data was from R. L. Polk & Co.'s National Vehicle Population Profile ® current as of October 2002 and from R. L. Polk & Co.'s TIPNet ® current as of March 2003. See Exhibit 2, http ://www.gaepd.org/Files_PDF/plans/sip/exhi bit_2_2002_registratio n_distributions.pdf , for more details on the registration distributions by age.

23 "EPA encourages and recommends the use of actual locality-specific...registration distributions by age in the development of SIP emission inventories. One exception to this would be areas having relatively few local HDDV registrations, but significant interstate tr ucking activity within the local area. Such areas may want to retain and use the [MOBILE] national registration distributions." Section 2.2.3.6, User's Guide to
MOBILE5

. 24 In 1999, Georgia's two-phase gasoline sulfur control program limited average sulfur in gasoline sold in the 13-county Atlanta area and in 12 surrounding counties to 150 parts per million (ppm). In addition, there is a seasonal (June 1 to September 15) 7.0 pounds per square inch (psi) Reid vapor pressure (RVP) cap on gasoline sold in this Phase 1 area. In 2003, Phase 2 of Geor gia's gasoline rule reduced average sulfur to 30 ppm and added 20 additional counties outside the 20-county ozone nonattainment area to the sulfur and (seasonal) RVP control program.

25 See Rules for Enhanced Inspection and Maintenance, Chapter 391-3-20, http ://www.gaepd.org/Files_PDF/rules/rules_exist/391-3-20.pdfMobile Source Emissions Modeling for Atlanta Ozone RFP Plan

C-16 model year vehicles; a check for catalytic converter tamp ering on 25-year-old through 1995 model year vehicles; and a gas cap pre ssure test on all s ubject vehicles.

Additional detail related to de velopment of emission factors used for the Ozone RFP Plan emissions inventory is provide d in Appendix C, Exhibit 3 ( http ://www.gaepd.org/Files_PDF/plans/ sip/exhibit_3_PlanAssumptions_102808.pdf ).



## Emission Inventory Files

The MOBILE6 input variables ar e specified in the input f iles. Exhibit 5 contains
abbreviated versions of the MOBILE6.2 i nput files used to model link-level,
nonattainment area emission factors for the 2002 Base and Adjusted Base Years. There is a separate scenario in each input for each speed, with only the speed varying. To conserve space, most of the speed sc enarios are omitted from these inputs: http ://www.gaepd.org/Files_PDF/plans/sip/e xhibit_5_base_and_adj _base_inputs_ozone_ rfp.pdf

Exhibit 6 contains abbreviated versions of the input files used to calculate emission
factors for the 2008 nonattainment area MVEB inventories: http ://www.gaepd.org/Files_PDF/plan s/sip/exhibit_6_2008_inputs.pdf

Exhibit 7 is a compressed file contai ning the complete MOBILE6.2 input files (filename.IN), plus the output (filename. TXT), post-processed output (filename.PRN) and supporting files (filename.D) used in modeling the mobile source emission inventories for the Ozone RFP Plan MVEB (a ll these files are in ASCII text format): http://www.gaepd.org/Files_PDF/plans/si p/exhibit_7_mobile_files_ozone_rfp.zip

Loaded network files that list VMT, speeds, FIPS 26 code, facility type code, HPMS functional class code, VOC a nd NOx, etc., by time of day for each network link are produced by the emissions calculation model. These files were imported into database tables and daily emissions were then summari zed. The data tables and the SQL queries
used to summarize 2002 and 2008 link-level em issions are contained in a compressed
Microsoft Access file available here: http ://www.gaepd.org/Files_PDF/plans/ sip/02_and_08_network_database.zip

File size: 27 megabytes comp ressed, 74 megabytes expanded.

26 Federal Information Processing Standard, a nu merical code indicating state and county.