State and Federal Standards for Mobile-Source Emissions (2006) / Chapter Skim
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2 Air Quality, Emissions, and Health Impacts Overview
2 Air Quality, Emissions, and Health Impacts Overview
Pages 21-64
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The management framework has five goals: mitigate ambient concentrations of criteria pollutants (described below) , limit exposure to hazardous air pollutants (HAPs)
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. The federal CAA Amendments of 1970 directed EPA to set National Ambient Air Quality Standards (NAAQS)
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The current federal and California standards are presented in Table 2-1. Nonattainment Areas The CAA mandates that ambient concentrations of criteria pollutants be monitored in urban and rural areas throughout the United States.
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24 yar im rd 23.0 Pr )
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25 ht s heal tration )
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assessment of air quality management credits the CAA with these substantial emissions reductions despite growth in population, energy use, and vehicle activity. The exceedances of the NAAQS, however, differ in relative severity from location to location and over time, depending on emissions sources, prevailing meteorology, and ef
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Because of effective regulation of CO emissions, especially from mobile sources, the number of CO nonattainment areas has been reduced from many to only a few, representing another area of success due to the CAA (NRC 2003; Holmes and Russell 2004)
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500 450 400 (ppb) 350 one 300 Ozr 250 1-H 200 Max 150 100 50 0 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 Year New York Airshed Los Angeles Airshed Standard FIGURE 2-4 Trends in maximum ozone concentrations averaged over 1 hr for New York and Los Angeles airsheds from 1978 to 2004.
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For example, EPA analyses show that mobile-source emissions standards programs already in place will yield significant reductions of mobile-source HAPs (EPA 2000a)
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Figure 2-6 shows a schematic representation of ozone and secondary PM formation and the relationships among the atmospheric processes involved in their formation. Later sections expand on the contribution of mobile sources to the concentrations of ozone and fine PM.
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Because ozone formation is driven by sunlight, as are other important radical reactions, ozone formation (and concentrations) is typically at a maximum in the afternoon and at a minimum before sunrise; however, ozone concentrations also depend on the temporal patterns of emissions and concentrations of available NOx and HCs.
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The California Air Resources Board uses reactive organic gas (ROG) emissions.
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VOC emissions reductions might be appropriate if conditions in an urban area are in the VOC-limited regime, whereas NOx emissions reductions might be appropriate if conditions are NOx-limited. In some cases, both NOx and VOC control might be appropriate.
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, SO2, and NOx, and are considered secondary PM. Elemental carbon is exclusively primary; however, a fraction of organic carbon in PM2.5 was found to be secondary.
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MOBILE-SOURCE EMISSIONS CHARACTERIZATION Fraction of Overall Inventory Emissions of air pollutants are generally divided into the source categories shown in Table 2-2. Mobile sources compose a large fraction of the overall inventory.
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· Nonroad mobile sources encompass a wide variety of equipment types that either move under their own power or are capable of being moved from site to site. Nonroad mobile equipment sources are not licensed or certified as highway vehicles but are defined as those that move or are moved within a 12-month period and are covered under EPA's emissions regulations as nonroad mobile sources.
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30,000 NOx Emissions raeYreP 25,000 20,000 Tonst 15,000 horS nda 10,000 Thous 5,000 0 1970 1975 1980 1985 1990 1995 2000 Year c. 40000 VOC Emissions raeYreP 35000 30000 Tonst 25000 horS 20000 nda 15000 Thous 10000 5000 0 1970 1975 1980 1985 1990 1995 2000 Year Fuel Combustion Industrial Processes On-road Nonroad - Miscellaneous FIGURE 2-10 Trends in (a)
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Diesel exhaust is a significant contributor of particles in the ultrafine size range. Studies have shown diesel exhaust to include particles ranging from 0.01 to 0.3 µm, with the most found in the lower end of the size distribution (Park et al.
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. ON-ROAD MOBILE-SOURCE EMISSIONS On-Road Vehicle Types Approximately 236 million vehicles were registered in the United States in 2003 (FHWA 2005)
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engines. Although those vehicles are a small fraction of the total fleet, they contribute proportionally more to total vehicle miles traveled (VMT)
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. On-Road Emissions Estimation Emissions Modes Mobile-source emissions are generally characterized as exhaust or evaporative emissions.
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42 8 Buses 548, 96. 6 Motorcycles 771, .0 50 ore kscu Tr Type Tir 6 le,x Vehicleyb 2-Ait oniatnibmoCd ption Une-lg an re,o 68,2 Sin M 27 75.
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. These distributions of emission types are broadly representative of actual conditions, but as discussed below, the models used to estimate exhaust and evaporative emissions include important uncertainties.
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. Emissions factors for light-duty on-road mobile sources are typically reported as mass pollutant per distance traveled (for example, grams of NOx/mile)
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Emissions Modeling EPA has developed the MOBILE model for estimating on-road mobile-source emissions in the United States. The model was established in the 1970s to estimate the variability in vehicle emissions factors across the fleet.
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, models the variation in emissions factors across roadway type, vehicle type, vehicle age, driving speeds, ambient conditions, fuel types, and different types of emissions-control programs. Vehicle emissions rates are typically estimated as a function of a zero-mileage, new-car emissions factor and the deterioration of the emissions factor over time.
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· Emissions factors for heavy-duty diesel vehicles and nonroad vehicles. · Emissions factors for HAPs and PM from all mobile sources.
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18,000 VOC Emissions 16,000 raeYreP 14,000 12,000 Tonst 10,000 horS 8,000 nda 6,000 Thous 4,000 2,000 0 1970 1975 1980 1985 1990 1995 2000 Year c. 14,000 NOx Emissions 12,000 raeYreP 10,000 Tonst 8,000 horS 6,000 nda 4,000 Thous 2,000 0 1970 1975 1980 1985 1990 1995 2000 Year LD vehicle LD truck HD gas vehicle HD diesel vehicle Other FIGURE 2-13 Historical trends in mobile-source (a)
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3000 b NOx Emissions 2500 y Dar Pe 2000 Tons egare 1500 Avl 1000 Annua 500 0 1975 1980 1985 1990 1995 2000 2003 Year c. 4500 ROG Emissions 4000 y Dar 3500 Pe 3000 Tons egare 2500 2000 Avl 1500 Annua 1000 500 0 1975 1980 1985 1990 1995 2000 2004 Year LD vehicle LD truck HD gas vehicle HD diesel vehicle Other FIGURE 2-14 Historical trends in mobile-source (a)
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The uncertainties related to emissions modeling and VMT estimates discussed above apply to these emissions estimates. NONROAD MOBILE SOURCES AND EMISSIONS Nonroad Vehicle and Equipment Types and Emissions Estimation Nonroad sources comprise a wide variety of vehicles and equipment with many different uses as listed in Table 2-5.
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· Construction and mining equipment, such as graders and backhoes. · Lawn and garden equipment, such as leaf blowers and lawn mowers.
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Lawn and garden equipment, recreational land, and recreational marine equipment are the three largest sources of CO and VOC or ROG nonroad inventories nationwide and in California. In contrast, nonroad NOx emissions are dominated by locomotive, commercial marine, construction, and mining equipment.
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NOx, and (c) VOC emissions in the United States by equipment class, 1970-2002.
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NOx, and (c) ROG emissions in California by equipment class, 1975-2004.
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Spatial and Temporal Variability in Mobile-Source Emissions In addition to the factors discussed above, variability in emissions inventories may affect variability in air quality between and within regions. On-road and nonroad mobile sources are significant contributors to emissions inventories in all major urban areas.
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. Such primary pollutants emitted from motor vehicles will not have uniform concentrations across a region, and spots with higher concentrations of ambient pollutants can occur at discrete locations.
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Minimal ozone concentrations in urban areas on weekday mornings are common and are attributed to commuter traffic NO emissions that chemically remove ozone, as described previously. Ozone has also been observed to be as high or higher on weekend days than on weekdays in some urban areas, which is known as the weekend ozone effect.
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AIR QUALITY HEALTH EFFECTS FROM EXPOSURE TO MOBILE SOURCES Effects on health resulting from exposure to air pollutants depend on a large number of variables, including the contaminants present during the exposure, the toxicity of the contaminants, their concentrations and durations of exposure, the dose, and the health status of the person exposed. Exposure to mobile-source air pollutants typically occurs within the context of exposure to a host of air pollutants from a host of sources, and health effects are probably due to exposure to the mixture and not to any one contaminant or source.
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(2002) discussed how exposure to motor vehicle CO emissions results in a substantial number of accidental deaths and estimates the number of accidental CO poisonings that have been prevented as a result of more stringent CO emissions standards.
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The health effects of a few mobile-source organic compounds that are considered HAPs are described below. 1,3 Butadiene 1,3-Butadiene is generated by incomplete combustion of gasoline and diesel fuel.
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Air Quality, Emissions, and Health Impacts Overview 61 Benzene Both on-road and nonroad gasoline-powered mobile sources contribute benzene to the ambient air. Benzene is a known human carcinogen and is associated with the development of leukemia.
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Studies examining health effects related to exposure to PM from mobile sources have primarily focused on diesel exhaust. Diesel exhaust, which includes hundreds of organic compounds and includes particles in the ultrafine size range, was designated as probable human carcinogen by IARC (1989)
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. CONCLUSIONS Substantial progress has been made over the past few decades in reducing air pollutant emissions from many sources, including mobile sources.
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The result is that different levels of controls on mobile and nonmobile sources are typically required for different areas in the Unites States.
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