APPENDIX E

Philadelphia, PA portion of the PhiladelphiaWilmington, PA-NJ-DE Nonattainment Area:

Emissions Inventory for the PM2.5 NAAQS

Technical Support Document

Mobile Source Highway Emissions Inventory

Executive Summary

July 2009

 Prepared for:

Mobile Sources Section, Bureau of Air Quality

Pennsylvania Department of Environmental Protection

PO Box 8468

Harrisburg, PA 17105-8468

 Prepared by:

Michael Baker, Jr., Inc.

1304 Concourse Drive

Linthicum, MD 21090

410-689-3400
Philadelphia, PA portion of the Philadelphia-Wilmington, PA-NJ-DE Nonattainment 

Area: Mobile Source Emissions Inventory

Executive Summary

July 2009

Table of Contents

INTRODUCTION .......................................................................................................................................................1

METHODOLOGY.........................................................................................................................................................1

INVENTORY SUBMISSION MATERIALS .......................................................................................................................2

DATA SOURCES AND ANALYSIS TOOLS...........................................................................................................3

ANALYSIS TOOLS ......................................................................................................................................................3

TRAFFIC DATA SOURCE/FLEET DATA INPUTS ...........................................................................................................4

TRAFFIC GROWTH ASSUMPTIONS..............................................................................................................................4

I/M AND FUEL PARAMETERS .....................................................................................................................................6

WEATHER DATA........................................................................................................................................................7

OTHER INPUTS...........................................................................................................................................................8

RESOURCES...............................................................................................................................................................9

List of Tables

TABLE 1: SUMMARY OF APPENDICES............................................................................................................................2

TABLE 2: SUMMARY OF INVENTORY ANALYSIS TOOLS ................................................................................................3

TABLE 3: PHILADELPHIA, PA PORTION OF NONATTAINMENT AREA VMT GROWTH ASSUMPTIONS .............................6

Summary of Appendices

Appendix E-1: Mobile Source Highway Emissions Inventory – An Explanation of Methodology

Appendix E-2: Philadelphia, PA Portion of Nonattainment Area PM2.5 Emissions Results 

(By Year, Functional Class and Vehicle Type)

Appendix E-3: MOBILE6.2 Input Parameter Summary

Appendix E-4: MOBILE6.2 Sample Input Files

Appendix E-5: Traffic Growth Forecasting System
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INTRODUCTION

This technical document supports the PM2.5 State Implementation Plan (SIP) for the Philadelphia, PA 

portion of the nonattainment area (Bucks County, Chester County, Delaware County, Montgomery 

County and Philadelphia County), Pennsylvania. To meet the emission inventory requirements of section 

172(c)(3) of the Clean Air Act, a regional mobile source highway inventory has been prepared for direct

and precursor PM2.5 emissions.

The pollutants included in the inventory are primary emissions (including condensibles) of PM2.5 , PM10

and the precursor emissions of VOC, CO, NOx, SO2, and NH3. 

This document provides the 2002 base year and 2009 projections of mobile (highway) vehicle miles of 

travel (VMT) and annual PM2.5 direct and precursor emissions that are needed to satisfy the SIP 

requirements. The following sections summarize the methodology and data inputs used to produce the 

mobile emissions inventory.

Methodology 

Guidance documents from EPA have been used to develop the base and future year emissions inventories 

for the Philadelphia, PA portion of nonattainment area. They include:

 Guidance for Creating Annual On-Road Mobile Source Emission Inventories for PM2.5 

Nonattainment Areas for Use in SIPs and Conformity, US EPA Office of Transportation 

and Air Quality, dated August, 2005.

 User’s Guide to MOBILE 6.1 and MOBILE6.2, Mobile Source Emission Factor Model, 

EPA420-R-02-028, dated August 2003.

 Technical Guidance on the Use of MOBILE6.2 for Emission Inventory Preparation, US 

EPA Office of Air and Radiation, and Office of Transportation and Air Quality, dated 

August 2004.

Mobile source emission factors have been calculated using EPA’s MOBILE6.2 emission model. The 

methodologies used to produce the emission results conform to the recommendations provided in the 

above guidance documents. A mix of local data and national default (internal to MOBILE6.2) data has 

been used for this submission. Local data has been used for the primary data items that have a significant 

impact on emissions. These include:

 VMT and speeds

 Vehicle type mixes

 Vehicle age distributions 

 Hourly distributions 

 Temperatures/humidity 

 Inspection/Maintenance parameters 

 Fuel program characteristics 

For this submission, the 2002 base year emission estimates are consistent with past analyses and 

submissions utilizing 2002 traffic and environmental data. Future year estimates for 2009 are based on 

the latest available 2005 traffic data, PENNDOT growth rates, and environmental parameters. Current

assumptions are used for control strategies (e.g. Inspection-Maintenance, Pennsylvania Clean Vehicle
2

programs) and fuel characteristics. The analysis methodology is consistent with past statewide inventory 

efforts including the 2005 National Emissions Inventory (NEI) submission. Annual VMT and emissions 

are produced using a sum of 12 monthly analysis scenarios. A detailed methodology is provided in 

Appendix E-1. Detailed information on the Commonwealth’s Traffic Growth Forecasting System is 

provided in Appendix E-5. The following sections address the key input data sources and analysis tools 

used for the preparation of the emissions inventory. 

Inventory Submission Materials 

To complement this document, attachments have been provided with additional detail regarding the 

analysis methodology, the MOBILE6.2 input parameters, and the output VMT and emission results for

the region. These include:

Table 1: Summary of Appendices

Appendix Title Description

E-1

Mobile Source Highway 

Emissions Inventory –

An Explanation of 

Methodology

Provides summary of methodology used to calculate 

the VMT and emissions.

E-2

Philadelphia, PA portion 

of Nonattainment Area

PM2.5 Emission Results 

(By Year, Functional 

Class and Vehicle Type)

Provides county by functional class and county by 

vehicle type annual emission tables for 2002 and 2009.

E-3

MOBILE6.2 Input 

Parameter Summary

Provides summary of input parameters related to traffic 

data sources, fuel, weather, I/M, and other MOBILE6.2 

related parameters.

E-4

MOBILE6.2 Sample 

Input File Provides examples of the MOBILE6.2 input files.

E-5

Traffic Growth 

Forecasting System

Provides detailed explanation of the Commonwealth’s 

revised methodology for VMT forecasting based on 

socioeconomic and demographic projections.
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DATA SOURCES AND ANALYSIS TOOLS 

This section provides a summary of the key input data and analysis tools used for producing the regional 

emissions inventory. The key elements to the modeling protocol are described in the sections below. A

more detailed description of the analysis process and tools is provided in the methodology report in 

Appendix E-1 and E-5. 

Analysis Tools 

The inventory analysis utilizes several key software/programs for producing the county emissions totals. 

These tools are outlined in Table 2.

Table 2: Summary of Inventory Analysis Tools

Tool Purpose

MOBILE6.2 Produces emission factors for each pollutant in 

Grams/Mile for direct PM2.5 and NOx

PPSUITE

Processes the highway data, Calculates hourly 

congested speeds for each state roadway 

segment, Prepares MOBILE6.2 input files, 

Processes MOBILE6.2 output files

Custom SCC Output 

Reformatting Program

Prepares output database files by EPA’s Source 

Classification Codes (SCC)

The inventory reflects the highway mobile source emission estimations using EPA’s MOBILE6.2

emission model, which accounts for changes in vehicle technology and regulations. MOBILE6.2 is a 

software application program that provides estimates of current and future emissions from highway motor 

vehicles. All states other than California must use MOBILE6.2 for the development of SIP and 

conformity emission analyses. The model can estimate both direct particulate matter emissions and the 

emissions of certain particulate precursors for cars, trucks, buses, and motorcycles.

PPSUITE represents an enhanced version of the Post Processor for Air Quality (PPAQ) software system 

that has been used for previous inventory and conformity submissions in Pennsylvania. The software has 

undergone significant revisions to ensure consistency with the MOBILE6.2 emissions model. PPSUITE 

plays a key role in the development of hourly roadway speed estimates, which are supplied as input to the 

MOBILE6.2 model. The software is also used to prepare the MOBILE6.2 input shell and to process the 

MOBILE6.2 outputs. 

Custom programs have also been prepared to translate the VMT and emission results into a database file 

indexed by EPA’s Source Classification Code (SCC). This code represents combinations of vehicle type 

groupings, functional classes, and time periods. 
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Traffic Data Source/Fleet Data Inputs 

The PENNDOT Roadway Management System (RMS) data serves as the primary highway data source

for the county and functional class VMT estimates. The data source is used to provide a “snapshot” of the 

regional roadway system and volumes in 2002 and 2005. The data includes the average annual daily

traffic (AADT) volumes for all state roadways in Pennsylvania. To account for additional local roadway 

VMT and to ensure consistency with reported HPMS totals, the 2002 and 2005 VMT totals are adjusted 

to match the annual HPMS VMT totals reported to FHWA. 

Annual VMT and emission results are based on a MOBILE6.2 analysis for an average day in each of the 

12 months. These results are then expanded to monthly sub-totals and then to an annual total. The daily 

and monthly seasonal factors, used to adjust the AADT traffic volumes, are developed from data 

contained in the document, 2005 Pennsylvania Traffic Data, as prepared by PENNDOT’s Bureau of 

Planning and Research. The seasonal and daily factors provided in this document are based on statistical 

analyses of 2005 traffic counts taken at permanent and in-pavement ATR (automatic traffic recorder) 

locations throughout the state. The factors are used to adjust AADT volumes to an average day in each 

month, and the PPSUITE software calculates unique congested speeds for each roadway segment.

PPSUITE calculates congested speeds by hour of the day for each roadway segment and provides the 

information as input to the MOBILE6.2 software. To disaggregate the daily RMS volumes to hourly 

volumes, auto and truck hourly pattern data from PENNDOT’s 2005 Pennsylvania Traffic Data report are 

used to determine the temporal variations of future year traffic volumes.

Vehicle mix patterns are calculated for each county / functional class grouping utilizing a combination of 

2002/2005 RMS truck percentages and MOBILE6.2 default vehicle mix distributions. The development 

of vehicle type pattern data input to the MOBILE6.2 software is described in more detail in Appendix E1. The distribution of vehicles to fuel type (diesel, gas) is determined from the MOBILE6.2 default diesel 

sales fractions.

Vehicle age distributions are input to MOBILE6.2 for each county based on registered vehicles that 

reflect July 1 summer conditions. These distributions reflect the percentage of vehicles in the fleet up to 

25 years old and are listed by the 16 composite MOBILE6 vehicle types. 2002 and 2005 vehicle age 

distributions have been used for this inventory from the PENNDOT Bureau of Motor Vehicles 

Registration Database. Due to insufficient data, only data for light-duty vehicles are used as local inputs. 

The heavy-duty vehicles use the internal MOBILE6.2 defaults.

Traffic Growth Assumptions 

Traffic forecasting plays a pivotal role in estimating future year emissions for each Pennsylvania county 

and region. The expected volume of traffic, measured in vehicle miles of travel (VMT), needs to be 

estimated for each county, or group of counties, for each relevant future year. This becomes the basis for 

further disaggregation of VMT to the roadway types on which the miles are expected to occur, vehicle 

types and vehicle age. 

This PM2.5 inventory utilizes a VMT growth rate projection methodology developed by PENNDOT as 

documented in the report “Statistical Evaluation of Projected Traffic Growth, Traffic Growth Forecasting 

System: Final Report, March 14, 2005”. As part of that study, a statewide traffic growth forecasting 

system was developed that incorporates traffic data from PENNDOT’s Traffic Information System and 
5

available socioeconomic forecasts. The study methodology has been shared among PENNDOT, DEP, 

and other interagency consultation group members, including the Pennsylvania Air Quality Work Group 

(which includes EPA, FHWA, and representatives from larger PA Metropolitan Planning Organizations 

(MPOs), and approved by PENNDOT. The methodology contains the following improvements over past 

statewide forecasting approaches:

 Strong statistical basis and consistent with state of the art.

 Thorough documentation of approach vs. alternatives.

 Increased data robustness through the inclusion of both county-level historical traffic trends 

from the PENNDOT Roadway Management System (RMS) databases (the basis for VMT 

reporting to the Federal Highway Administration of USDOT through the Highway 

Performance Monitoring System (HPMS) and county-based demographic projections from 

an independent 3rd party (Woods and Poole Economics, Inc.).

 Expedient and inexpensive update process. 

The data inputs to the traffic growth forecasting system are periodically updated to produce revised 

forecast growth factors for each county in the state. The frequency of this update is at least every 5 years, 

consistent with EPA and FHWA “Latest Planning Assumptions” guidance. 

The most recent available forecasts, used in the development of this inventory, include historic HPMS 

VMT through 2005 and use of the 2006 State Profile, developed by Woods & Poole Economics. The 

2006 State Profile includes historical demographic data and forecasts by year from 1969 through 2030 for 

every county and Metropolitan Statistical Area (MSA) in Pennsylvania. The county VMT forecast 

growth rates are developed for four functional classifications in each county: urban interstate, urban noninterstate, rural interstate and rural non-interstate. The PENNDOT statistical VMT forecasting model 

incorporates historical VMT trends, socio and economic data (households, mean household income), and 

a relative measure of transportation capacity (lane miles per capita). 

The forecasts used for this annual PM2.5 emissions inventory have been developed to account for potential 

variability in future regional VMT growth. Variability from the base forecast may be caused by multiple 

factors which influence vehicle travel, many or most of which may be influenced by outside factors or 

events. The county-level growth rates from the PENNDOT VMT forecasting system have been evaluated 

to determine an overall regional growth rate for the nonattainment area. Growth rates were examined for 

counties within the nonattainment area and for nearby counties that might impact future conditions within 

the region. 

Table 3 summarizes the assumed projected growth of VMT for future analysis years within the 

nonattainment area.
6

Table 3: Philadelphia, PA Portion of Nonattainment Area VMT Growth Assumptions

Analysis

Year

Total Growth 

From 2002

Annualized Growth 

From Previous 

Analysis Year

Bucks County

2002 ----- -----

2009 15.6% 2.2%

Chester County

2002 ----- -----

2009 15.6% 2.2%

Delaware County

2002 ----- -----

2009 18.9% 2.7%

Montgomery County

2002 ----- -----

2009 16.5% 2.4%

Philadelphia County

2002 ----- -----

2009 17.7% 2.5%

I/M and Fuel Parameters 

The Inspection Maintenance (I/M) program inputs to the MOBILE6.2 model are based on past and 

current programs within the Philadelphia area. 

Pennsylvania’s first inspection and maintenance (I/M) program was implemented in 1984 which required

applicable vehicles to undergo an annual one-speed idle test. This basic I/M program applied to modelyear 1975-1980 gasoline cars and light duty trucks up to 9,000 pounds GVW registered in the 5-county 

Philadelphia region (Bucks, Chester, Delaware, Montgomery and Philadelphia counties) and the 4-county 

Pittsburgh metropolitan region (Allegheny, Beaver, Washington and Westmoreland counties). 

In October 1997, Pennsylvania began an enhanced I/M Program to include ASM 5015 tailpipe testing, 

two-speed idling test, gas cap and visual anti-tempering inspection. Model-year 1981 and newer cars and 

light duty trucks registered in the above nine counties in the Philadelphia and Pittsburgh regions are 

subject to the enhanced I/M Program. New model years are exempt for the first year.

The Commonwealth’s I/M program was upgraded and expanded throughout the state with a phase-in 

period starting in December 2003 and fully implemented by June 2004. The program test requirements 

vary by region and include on-board diagnostics (OBD) technology that uses the vehicle’s computer for 

model years 1996 and newer to download potential engine problems that could effect emissions. The 

program, named PAOBDII, is implemented in the Philadelphia, Pittsburgh, and South Central / Lehigh 

Valley Regions. The Northern Region receives gas cap and visual inspections and the other 42 counties 
7

in the Commonwealth receive a visual inspection. Vehicles subject to the program include 1975 and 

newer model year gasoline cars and light duty trucks up to 9,000 pounds GVW. New model years are 

exempt for the first year. The county of registration determines which inspections are required. 

The 2002 I/M program inputs to the MOBILE6 model for the 5-county Philadelphia region include a 

PA97 with ASM I/M program and phase-in cutpoints. The I/M program parameters include:

Model Years Program Parameters

1981 & newer ASM5015 with Phase-in

1975 & newer Gas Cap

1975 – 1980 Idle

1975 & newer ATP

The 2009 I/M program inputs to the MOBILE6 model for the Philadelphia region include a PAOBDII 

and PA97 with ASM I/M program and final cutpoints. The I/M program parameters include:

Model Years Program Parameters

1996 & newer PAOBDII

Gas Cap

1981 – 1995 ASM 5015 Final

1975 – 1995 Gas Cap

1975 & newer ATP

The RVP values, varying by month, are consistent with values used for past inventory efforts. These 

assumptions, as well as the I/M program and fuel parameters, are summarized in Appendix E-3.

Weather Data 

Updated weather information has been obtained from the National Climatic Data Center to calculate the 

minimum and maximum temperatures and absolute humidity data inputs to the MOBILE6.2 model. 

These assumptions are consistent with the 2005 NEI inventory submission. Average minimum and 

maximum temperatures and barometric pressure values for each month were obtained for each of the 

weather station locations in Pennsylvania. In addition, average relative humidity values were obtained for 

6-hour intervals (4 intervals during a 24 day period) for each of the 12 months. Absolute humidity values

by month were then calculated from the relative humidity, barometric pressure, and temperature for each 

of the 4 daily intervals using EPA’s M6HUMID program. The lowest of these 4 values for each month is 

determined to be the absolute humidity for that month.

Other weather data required by MOBILE6.2 are assumed as the program defaults. These include the 

cloud cover, peak sun, and sunrise/sunset options. 
8

Other Inputs 

Federal Programs

Federal vehicle emissions control and fuel programs are incorporated into the MOBILE6.2 software. The 

programs include:

 The Federal Motor Vehicle Control Program (FMVCP) including the National Low Emission 

Vehicle Program (NLEV) and federal Tier II / Low Sulfur Fuel Program;

 Emissions standards for medium and heavy duty vehicles in 2002, 2004 and 2007;

 Stage II and Onboard Refueling Vapor Recovery (ORVR).

Note: Pennsylvania considers emissions from refueling operations an area source category. While 

MOBILE6.2 is employed to calculate emissions factors for that source category, refueling emissions are 

not included in highway vehicle emissions estimations.

State Programs 

The MOBILE6.2 software also allows for modeling of permissible state activities control emissions from 

highway vehicles. 

In 1998, Pennsylvania promulgated the New Motor Vehicle Emissions Control Program. This program 

created the Pennsylvania Clean Vehicles Program that required new light-duty highway motor vehicles 

offered for sale within Pennsylvania to be certified by the California Air Resources Board (CARB) under 

that Board’s Low Emitting Vehicle (LEV) program. The Pennsylvania Clean Vehicles Program does not 

require the California Zero Emitting Vehicle (ZEV) requirement. As a compliance alternative to the 

Pennsylvania Clean Vehicles Program, automakers have elected to comply with the National Low 

Emission Vehicle (NLEV) program. The NLEV program began phase-in starting in model year 1999. 

The Pennsylvania rules allow the NLEV compliance option for the duration of Pennsylvania’s 

participation in the NLEV program. Pennsylvania is in the process of amending the Pennsylvania Clean 

Vehicles Program to initiate in model year 2008. As a result, the modeling results assume a 2008 start 

year for the Pennsylvania Clean Vehicles Program. Benefits from this program are realized in 2008 and 

beyond. 

The methodology employed to estimate the benefits of adopting CA LEV II emissions standards is 

consistent with the approach provided in the EPA’s June 2002 Guidance (Modeling Alternative NLEV 

Implementation and Adoption of California Standards in MOBILE6, June 5, 2002). The approach 

assumes:

 Tier2 phase-in schedule consistent with MOBILE6.2 defaults

 LEVII phase-in schedule as provided in EPA’s June 2002 Guidance

 Assumes PZEV and AT-PZEV vehicles share the same evaporative emissions as LEVII/Tier2 

vehicles

Appendix E-4 contains the modified MOBILE6.2 files used to model the above assumptions. They are 

consistent with the June 2002 EPA guidance.

The federal Tier 2 / Low Sulfur Fuel Program took effect in 2004 and in practicality supplanted the 

NLEV program for new light-duty vehicles. 
9

RESOURCES 

Guidance for Creating Annual On-Road Mobile Source Emission Inventories for PM2.5 

Nonattainment Areas for Use in SIPs and Conformity, US EPA Office of Transportation and Air 

Quality, dated August, 2005.

Consolidated Emissions Reporting, Federal Register, June 10, 2002

2005 Pennsylvania Traffic Data, PennDOT Bureau of Planning and Research, 2005. 

User’s Guide to MOBILE6.1 and MOBILE6.2, Mobile Source Emission Factor Model, EPA420-R-02-

028, dated August 2003.

Technical Guidance on the Use of MOBILE6 for Emission Inventory Preparation, US EPA Office of 

Transportation and Air Quality, August 2004.

Policy Guidance on the Use of MOBILE6 for Emission Inventory Preparation, US EPA Office of Air and 

Radiation, January 18, 2002.

Modeling Alternative NLEV Implementation and Adoption of California Standards in MOBILE6, EPA, 

June 5, 2002.

Technical Guidance on the Use of MOBILE6.2 for Emission Inventory Preparation, US EPA Office of 

Air and Radiation, and Office of Transportation and Air Quality, August 2004.

Statistical Evaluation of Projected Traffic Growth, Traffic Growth Forecasting System: Final Report, 

Michael Baker Jr., Inc., March 14, 2005.