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18 Exhibit 2-2. National air toxics assessment process (simplified). State and Emissions by Allocation County (NEI) HAPEM EPA data to tracts ASPEN 100+ toxics Cancer and Emissions by Concentrations Point HEM Non-Cancer Tract by Tract Area Risk by Tract On-Road Non-Road mates of emissions, including freight emissions. One of the Another example of a national-scale health risk assessment most influential studies is the National Air Toxics Assessment is the work that supports the periodic review of the NAAQS. (NATA). (15) NATA produces screening-level estimates of Under the Clean Air Act, EPA is required to periodically review cancer and non-cancer health effects of air toxics by census tract the NAAQS and, if warranted, modify them to protect public for the entire United States. NATA studies have been performed health and welfare. The decision to modify the NAAQS is based for 1996, 1999, and 2002, and work is continuing on studies for on epidemiological studies and on exposure modeling. Review 2005 and 2008. of the NAAQS also involves advice from an independent Clean As shown in Exhibit 2-2, NATA starts with county-level Air Scientific Advisory Committee (CASAC). emissions estimates from the NEI. The NEI includes all EPA has recently completed exposure modeling for the emissions sources (point, area, on-road mobile, and nonroad NAAQS review for two pollutants, NO2 and SO2. (1617) mobile) and is developed by state air quality agencies and EPA The studies focused on a small number of specific geographic for more than 100 air toxics as well as criteria pollutants. It locations, including Atlanta and Philadelphia for NO2 review, includes emissions from trucks, locomotives, marine vessels, and several counties in Missouri for SO2 review. Like NATA, aircraft, and nonroad equipment, although the emissions the exposure modeling starts with emissions data from the estimates can be simplistic due to the broad geographic scale. National Emission Inventory, although roadway emissions were County-level emissions in the NEI are allocated to census estimated using roadway link traffic volumes from regional tracts using spatial surrogates. Dispersion modeling is used to travel demand models. Dispersion modeling was done using estimate tract-level pollutant concentrations. For mobile and AERMOD, and exposure modeling was done using the Air area sources, dispersion modeling is done using the Assess- Pollution Exposure Model (APEX). These studies result in ment System for Population Exposure Nationwide (ASPEN) estimates of the number of individuals exposed to different model; for point sources, dispersion modeling is done using benchmark levels of air pollution, as illustrated in Exhibit 2-3. the Human Exposure Model (HEM). (Both these models The results of this exposure modeling supports the NAAQS are exposure models that include dispersion modules.) The review process and, in combination with results from epi- Hazardous Air Pollutant Exposure Model (HAPEM) is used demiological studies, could lead to change in the NAAQS, with to estimate exposure, using tract-level data on activity patterns far-reaching consequences for public agencies and industry and demographics. in affected regions. Because of its broad scope, NATA is primarily a screening tool, and EPA advises not to use the results by themselves to 2.2 Regional-Scale Applications identify toxics hotspots or pinpoint specific risk values by census tract. EPA uses the results of assessments in a variety Regional-scale application of freight emissions estimates of ways, including the following: includes the development of state implementation plans (SIPs) and related Transportation Conformity determinations, as Set priorities for improving emission inventories, well as regional-scale health risk assessments. Direct priorities in expanding EPA's air toxics monitoring network, 2.2.1 SIP Development More effectively target risk reduction activities, Identify pollutants and industrial source categories of great- When measured concentrations of a criteria pollutant within est concern, a geographic region are below those allowed by the NAAQS, Help set priorities for the collection of additional informa- EPA designates the region as an attainment area for that tion, and pollutant; regions where concentrations of criteria pollutants Improve understanding of the risk from air toxics. exceed federal standards are called nonattainment areas. Former

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19 Exhibit 2-3. Example of estimated number of asthmatic children with at least one NO2 exposure at or above health effect benchmark levels. Source: Risk and Exposure Assessment to Support the Review of the NO2 Primary National Ambient Air Quality Standard, EPA-452/R-08-008a (Washington, D.C.: EPA, November 2008), p. 199. nonattainment areas that have attained NAAQS are designated The regional emissions inventory is a critical element of the as maintenance areas. Each nonattainment area is required to SIP process because all modeling of concentrations depends develop and implement a SIP that documents how the region on knowledge of the emissions in the nonattainment area will reach attainment levels within periods specified in the (and sometimes the emissions upwind of the area as well). Clean Air Act. The regional emissions inventory is forecast to future years and The SIP typically includes (1) a discussion of the region's air compared to the emissions budget in order to track the area's quality issues, (2) a demonstration (using regional dispersion progress over time toward attainment. The emission inventory and photochemical modeling) of the emission reductions that identifies the contribution of each source type to the area's are needed to decrease concentrations of the nonattainment total emissions. The emission inventory informs the air quality pollutants to below the NAAQS, (3) a discussion of the regu- agency's planning process for developing, evaluating, and lations or programs proposed (usually by the state air quality selecting emission reduction strategies. Emission inventory agency for the area) to achieve the necessary emissions reduc- information also helps the agency allocate resources most tions, (4) an analysis of the emissions impacts of the selected efficiently to produce the greatest emissions reductions at the set of regulations or programs, and (5) evidence of federally lowest cost. enforceable commitments the agency has made to imple- Some attainment areas or regions within attainment areas ment the proposed regulations or programs. The attainment voluntarily develop emission inventories for planning purposes. demonstration establishes the target emissions level--the These purposes may include voluntary emission reduction "emissions budget"--that the area must achieve in order to initiatives and development of emission reduction strategies attain the NAAQS. in areas that anticipate becoming nonattainment areas in the The SIP inventory estimates primary emissions (those near future. produced directly by a source) of the nonattainment pollutant. Regional emission inventories follow the EPA classification The SIP modeling estimates secondary emissions (those pro- scheme that divides emission sources into point, area, and duced by chemical reactions of precursor pollutants in the mobile categories. Point sources are stationary sources that atmosphere). Thus, the inventory must also include emissions have a stack or other definable location from which emissions of any precursors to the nonattainment pollutant, and the emanate (e.g., fossil-fueled electric power plant). Calculation modeling includes their atmospheric reactions that produce of the point source emissions inventory is relatively straight- the nonattainment pollutant. forward because characteristics of many sources are obtain-

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20 able from their required air quality permits. Area sources are areas that do not "conform" to the area's SIP. The purpose of generally point sources that are too small to inventory indi- this conformity requirement is to ensure that general activ- vidually, such as small dry cleaning establishments. Area source ities do not interfere with meeting the emissions targets in emissions are estimated using economic and demographic the SIPs, do not cause or contribute to new violations of the information where source-specific data are unavailable. Mobile NAAQS, and do not impede the ability to attain or maintain the sources usually are divided into on-road and off-road compo- NAAQS. The conformity rules apply only to criteria pollutants. nents for inventory purposes. On-road mobile sources consist The EPA has issued two sets of regulations to implement CAA of cars, trucks, motorcycles, and buses. Off-road mobile sources Section 176(c), as follow: consist of several diverse groups such as construction equip- ment, railroad locomotives, ships and boats, port cargo handling Transportation Conformity Rules (40 CFR 51, Subpart T), equipment, aircraft, and aircraft ground support equipment. which apply to transportation plans, programs, and projects Accordingly, in a regional emissions inventory, the sources of funded under Title 23, U.S. Code, or the Federal Transit Act. freight-related emissions are classified almost exclusively as Highway and transit infrastructure projects funded by on-road and off-road mobile sources. FHWA or the Federal Transit Administration (FTA) usually Since passage of the Clean Air Act Amendments (CAAA), are subject to transportation conformity. A region's FHWA- EPA has tightened its emission standards considerably on required long-range transportation plan also is subject to nearly all source categories. Many nonroad sources are subject Transportation Conformity. to retrofit requirements reducing emissions at the time of General Conformity Rules (40 CFR 51, Subpart W) apply to overhaul. This reduces emissions better than regulation that all other federal actions not covered under Transportation only addresses freshly manufactured equipment. Until recent Conformity. The General Conformity Rules established years, the nonroad mobile source category was a relative emissions thresholds, or de minimis levels, for use in eval- exception. As emission control requirements on other sources, uating the conformity of an action. General Conformity including highway vehicles, have become stricter, their relative typically applies at the project-scale for airports, seaports, shares of the total emissions inventory have shrunk. As a result, and military bases. the off-road mobile source category, which had been less heavily regulated and includes many engines with long life- In metropolitan regions within nonattainment areas, the times and consequent slow rates of replacement with cleaner federally designated metropolitan planning organization models, contributes an increasing share of the total emissions. prepares the FHWA-required long-range transportation plan, In recent years EPA, state air quality agencies, and port/airport which is subject to Transportation Conformity, as previously operators have focused greater regulatory attention on off-road noted. The conformity demonstration for the plan is based on mobile sources. This has included adoption of retrofit require- an emissions inventory for the highway system in the region ments for in-use (as opposed to new) equipment. Because a subject to the plan. This inventory usually is coordinated with, large proportion of off-road mobile sources are associated with or is a subset of, the nonattainment area's regional mobile source freight transport, the importance of freight-related emission emissions inventory. Exhibits 2-4 and 2-5 present example calculations for the off-road components of regional emission emissions tables from a regional conformity determination inventories is increasing. for a long-range transportation plan. Freight trucks are included in the traffic data (counted or projected traffic volumes by road segment) that are input to 2.2.2 Transportation Conformity the travel modeling that supports the plan's inventory cal- Section 176(c) of the Clean Air Act (CAA) prohibits federal culations. Although diesel-fueled trucks are relatively high agencies from taking actions in nonattainment or maintenance emitters of NOX and PM2.5 on a per vehicle basis, the emission Exhibit 2-4. Example of VOC emissions tables from a regional conformity determination for a long-range transportation plan. VOC Emissions (Tons per Summer Day) Region Action Statewide Action Difference Year Emissions Emissions Emissions Budget (Action Budget) 2000 n/a 166.5 n/a n/a 2007 22.7 62.0 86.7 -24.7 2010 18.7 49.7 86.7 -37.0 2020 13.5 29.8 86.7 -56.9 2030 12.9 28.7 86.7 -58.0

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21 Exhibit 2-5. Example of NOX emissions tables from a regional conformity determination for a long-range transportation plan. NOx Emissions (Tons per Summer Day) Region Action Statewide Action Difference Year Emissions Emissions Emissions Budget (Action Budget) 2000 n/a 287.9 n/a n/a 2007 63.8 174.1 226.4 -52.3 2010 48.3 129.2 226.4 -97.2 2020 24.3 45.4 226.4 -180.9 2030 20.2 34.7 226.4 -191.6 inventories for most Transportation Conformity demonstra- PATA). Ambient air pollution monitoring data are typically tions do not analyze trucks as a separate source category because compared to modeled concentrations in order to assess the truck volumes are a relatively small fraction of total traffic accuracy of the model. volumes and most long-range transportation plans contain The health risk assessments then use exposure models to few dedicated freight facilities. In contrast, where a nonattain- link ambient concentrations of pollutants with population, ment area is considering truck-oriented strategies to reduce activity, and other parameters to determine overall population emissions, the mobile source inventory for the area's SIP may exposure. An exposure model attempts to characterize the address heavy-duty diesel trucks in greater detail, especially activities and movement of individuals within a given area, in PM2.5 nonattainment areas. usually a census area, and from that estimate a range of con- centrations to which that population would be subject. For example, in a given census tract there are young children and 2.2.3 Regional Health Risk Assessments the elderly who remain indoors most hours of the day, older Freight emissions figure prominently in many health risk children who go to school or play outdoors, workers who assessments because freight transportation is a major source of commute to other areas, and others with a range of activities. diesel PM in many areas. A number of regions have prepared Varying ranges of activities expose individuals to different health risk assessments to better understand the relationship amounts of outdoor ambient air, or outdoor air as it infiltrates between emissions and public health at the metropolitan scale. buildings. An exposure model uses information from each Major studies include the following: census tract to estimate the range in age of the population, their activities, and commuting habits, and calculates a range Multiple Air Toxics Exposure Study III (MATES III) in the of concentrations to which they are exposed. (20) Toxicity factors for each pollutant are combined with expo- Los Angeles metropolitan area is led by the South Coast Air sure estimates to estimate health risk--the probability of an Quality Management District. (18) adverse health outcome. Risk can then be illustrated on a map Puget Sound Air Toxics Evaluation, led by the Puget Sound as shown in Exhibit 2-6. Clean Air Agency in conjunction with Washington State In most of these studies, diesel particulate matter is the dom- Department of Ecology. (19) inant source of cancer risk. For example, the MATES III study Portland Air Toxics Assessment (PATA), led by the Oregon found that the cancer risk from air toxics in the Los Angeles Department of Environmental Quality with Portland region is about 1,200 per million, and about 84% of that risk METRO and EPA. (20) comes from diesel exhaust. In many cases, freight transport is Houston Exposure to Air Toxics Study (HEATS) is a collab- the largest source of diesel emissions. orative study involving local universities, state, federal, and Regional health risk assessments are used by regional, state, local government agencies, and research organizations. (21) and federal agencies to develop more effective strategies to reduce risks to residents. In places like the Portland and Seattle These studies typically begin with a detailed inventory of air regions, which are in attainment for PM and ozone, the studies emissions, including the six priority mobile source air toxics have been used to support planning and investments in diesel (MSATs) defined by EPA as acetaldehyde, acrolein, benzene, emission reduction programs. Although these areas do not 1,3-butadiene, diesel particulate matter, and formaldehyde. violate federal air quality standards, they are still interested in (22) Air quality modeling is then used to estimate resultant reducing the negative health impacts of air toxics emissions. average pollutant concentrations throughout the region. Several For example, the PATA study is described as a "key step in different air quality modeling tools have been used for these a community planning process to reduce air toxics in the studies, including CAMx (for MATES III) and CALPUFF (for Portland area." (23)