Scope Study for Expanding the Great Lakes Toxic Emission Regional Inventory to include Estimated Emissions from Mobile Sources

Chapter 8 Framework for Computer Software Development

• 8-1. General Requirements
• 8-2. Tasks
• 8-3. References

This chapter provides a framework for developing a mobile source module for estimating toxic air emissions from mobile sources in the Great Lakes region. According to the previous analyses and discussion, the recommendation is to expand the automated Regional Air Pollutant Inventory Development System (RAPIDS) to support cooperative estimation of emissions of selected toxic compounds from mobile sources in the Great Lakes region. These emissions can then be aggregated with emission estimates from point and area sources to provide a more comprehensive estimate of toxic air emissions in the region.

The following sections describe the general requirements and major tasks for expanding RAPIDS.

8-1. General Requirements

The mobile source module for estimating toxic air emissions from mobile sources in the Great Lakes region should be built upon RAPIDS. The Import/Export, Quality Control (QC) Checker, Reports, and Estimator functions in RAPIDS should be modified to handle mobile source data as well as point and area source data. The mobile source module shall be consistent with all RAPIDS data screens and shall be developed to meet the level of detail recommended in Chapter 3. The mobile source module should be capable of estimating county-based, season-by-season emissions for highway vehicles, nonroad sources, aircraft, and locomotives. These emission sources and their subcategories are defined in the EPA’s guidance (EPA, 1992). The estimation in the module should include emissions of the seventy two pollutants, as identified in Table 3-2, that are emitted from mobile sources and are of concern in the Great Lakes basin. Since the mobile source emission inventory may be updated every three years, an appropriate growth factor algorithm should be incorporated in the module to project the emissions for the years when emission data are not collected.

8-2. Tasks

There are 6 major tasks in developing the mobile source module.

Task 1: Establish a Link between RAPIDS and Total Organic Gases (TOG) / Particulate Matter (PM) Emission Factors Provided by EPA Models, MOBILE5a and PART5, for Highway Vehicles

As pointed out in Chapter 4, combining TOG and PM emissions with speciation profiles is currently the most feasible approach for the Great Lakes States and Ontario in preparation of the regional toxic air emission inventory for highway vehicles. The TOG and PM emissions can be estimated by multiplying TOG and PM emission factors by activity levels. EPA models, MOBILE5a (or Canadian version MOBILE5c) and PART5 provide TOG and PM emission factors. These emission factors are specific to road functional class. They are different from county to county, season to season, and are unlike the existing emission factors, such as FIRE emission factors (EPA, 1996), which are spatially and temporally generic. Therefore, new algorithms need to be developed to link RAPIDS with TOG and PM emission factors provided by the MOBILE5a (or c) and PART5 models. New activity parameters also need to be added to RAPIDS to match activity data for highway vehicles.

Task 2: Develop an Algorithm in RAPIDS to Estimate Equipment Populations for Nonroad Mobile Sources

Chapter 5 indicates that the toxic air emissions from nonroad sources can be estimated by using toxic emission factors based on activity level or combining TOG and PM emissions with speciation profiles. Activity data are required in both approaches. Although activity parameters can be determined through surveys, in most cases the survey data are not available at the county level. Among the activity parameters, determining equipment populations in each category type at the county level is the most challenging. As an alternative, the county level equipment populations can be estimated by using a linear relationship between equipment population and activity indicator. In order to do so, the RAPIDS reference table will need to be expanded to include national nonroad equipment population and national activity indicator data and an algorithm will need to be established in the RAPIDS for the linear relationship between equipment populations and activity indicators.

It should be noted that for nonroad sources, most emission factors are for volatile organic compounds (VOC) not TOG. Therefore, appropriate conversion factors from VOC to TOG should be selected and incorporated into RAPIDS.

Task 3: Incorporate FAA Aircraft Engine Emission Database (FAEED) and Program to RAPIDS to Estimate the County Level HC and PM Emissions for Aircraft

As analyzed in Chapter 6, in concept, toxic air emissions from aircraft can be estimated by directly using toxic emission factors based on activity level. However, due to a lack of information on toxic emission factors, combining TOG and PM emissions with speciation profiles is the reasonable approach for now. The FAEED contains emission factors for various aircraft engines and data correlating engines to specific aircraft. The FAEED program is capable of computing the total HC and PM emissions produced by a specific fleet (EPA, 1995). The FAEED and FAEED program may need to be incorporated into RAPIDS for estimating the county level HC and PM emissions. In order to speciate HC emissions, the proper conversion factors from HC to TOG need to be selected and built into RAPIDS.

Task 4: Select Representative Emission Factors and Speciation Profiles and Incorporate Them into RAPIDS for All Categories of Mobile Sources

Under this task a database of emission factors and a database of speciation profiles should be compiled for all categories of mobile sources. These databases need to be compiled from a review of all available literature and should represent the most reliable and most current information. In addition, these databases should reflect emission conditions of the Great Lakes region for the purpose of estimating emissions of the seventy-two toxic air pollutants identified in Table 3-2. EPA publications or studies should be given first preference. Consideration should also be given to the information sources used by Environment Canada and the Ontario Ministry of the Environment. Whenever possible, information should be extracted from "primary" information sources. If "secondary" information sources are used, the contractor shall provide the primary references. A primary source is one who has conducted performance testing, has direct control over data, and is in a position to know the methods and limitations in sample collection and analysis. A secondary source is a compilation of referenced data from various primary sources.

A reliability or accuracy rating should be assigned to the emission factors and speciation profiles. This reliability or accuracy rating can be similar to that used by FIRE or to similar criteria used in EPA VOC/PM speciation manuals. It must be approved by the Steering Committee and shall be an integral part of the emission factor database or speciation profile database.

The efforts should be focused on the air toxic compounds of concern to the Great Lakes states and province, that are not included in the existing EPA speciation profiles and EPA FIRE database, such as POM emissions from mobile sources and 1,3-butadiene from diesel vehicles and engines. Efforts should also be specified to the development of emission factors and speciation profiles for diesel vehicles and engines, emission factors for PM and targeted toxic pollutants in a PM format, and PM speciation profiles for metals and compounds other than lead.

Task 5: Introduce Appropriate Growth Factor Algorithm to RAPIDS to Project the Emissions for the Years when Emission Data Are Not Collected

As recommended in Chapter 3, the regional mobile source emission inventory should be updated annually to be consistent with the regional emission inventory for point and area sources. Since a tremendous amount of work is required to prepare a mobile source emission inventory, Chapter 3 also suggested that an actual emission inventory be prepared every three years and growth factors should be used to project the emissions for the years when emission data are not collected. The growth factors can be calculated as the growth indicator ratio of the data for the emission projection year to the data for the year with actual emission estimates. The growth indicator is dependent on categories or sub-categories of mobile sources. Examples of growth factors are population data and fuel consumption data. Appropriate growth indicators should be selected for each source category (or subcategory) and corresponding algorithms should be introduced to RAPIDS.

Task 6: Modify and Enhance RAPIDS to Collaboratively and Effectively Estimate Emissions from Mobile, Point, and Area Sources

The existing RAPIDS has already been used to estimate point and area source emissions in the Great Lakes states and Ontario. However, some problems have been discovered in the RAPIDS performance. In order to collaboratively and effectively handle mobile source data as well as point and area source data, the Import/Export, QC Checker, Reports, and Estimator functions in RAPIDS should be modified and enhanced.

8-3. References

EPA, Factor Information Retrieval System (FIRE) Version 5.1a, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC, May 1996.

EPA, Procedures for Emission Inventory Preparation: Volume IV: Mobile Sources, U.S. Environmental Protection Agency, Office of Mobile Sources, Ann Arbor, MI and Office of Air Quality Planning and Standards, Research Triangle Park., NC, EPA-450/4-81-026d (Revised), 1992.

FAEED, FAA Aircraft Engine Emission User Guide and Database, U.S. Environmental Protection Agency Technology Transfer Network, Office of Mobile Sources (OMS) Bulletin Board System, 1995.