ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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rather than duration of the exposure is an important determinant of respiratory effects. Exposure to high SO2 concentrations may result in edema of the lungs or glottis and respiratory paralysis. Particulate Matter Respirable particulate matter with an aerodynamic diameter of 10 micrometers or less is referred to as PMIo• PMIo consists of particulate matter emitted directly into the air, such as fugitive dust, soot, and smoke from mobile and stationary sources, construction operations, fires and natural windblown dust, and particulate matter formed in the atmosphere by condensation and/or transformation of SO2 and ROG(EPA 2006a). Fine particulate matter(PM2.5) includes a subgroup of smaller particles that have an aerodynamic diameter of 2.5 micrometers or less(ARB 2006a). The adverse health effects associated with PMIo depend on the specific composition of the particulate matter. For example,health effects may be associated with metals,polycyclic aromatic hydrocarbons(PAH), and other toxic substances adsorbed onto fine particulate matter(referred to as the"piggybacking effect"), or with fine dust particles of silica or asbestos. Generally, adverse health effects associated with PMIo may result from both short- term and long-term exposure to elevated concentrations and may include breathing and respiratory symptoms, aggravation of existing respiratory and cardiovascular diseases, alterations to the immune system, carcinogenesis, and premature death(EPA 2007a). PM2.5 poses an increased health risk because the particles can deposit deep in the lungs and may contain substances that are particularly harmful to human health. Direct emissions of PMIo remained relatively unchanged between 1975 and 2005 and are projected to remain unchanged through 2020. PMIo emissions in the SJVAB are dominated by emissions from areawide sources, primarily fugitive dust from vehicle travel on unpaved and paved roads,waste burning, and residential fuel combustion. Direct emissions of PM2.5 decreased from 1975 to 2005 and are projected to continue decreasing through 2020. PM2.5 emissions in the SJVAB are dominated by emissions from the same areawide sources as PMIo(ARB 2006a). Lead Lead is a metal found naturally in the environment as well as in manufactured products. The major sources of lead emissions have historically been mobile and industrial sources. As a result of the phase-out of leaded gasoline, as discussed in detail below,metal processing is currently the primary source of lead emissions. The highest levels of lead in air are generally found near lead smelters. Other stationary sources are waste incinerators,utilities,and lead-acid battery manufacturers. Twenty years ago,mobile sources were the main contributor to ambient lead concentrations in the air. In the early 1970s,the U.S. Environmental Protection Agency(EPA) set national regulations to gradually reduce the lead content in gasoline. In 1975,unleaded gasoline was introduced for motor vehicles equipped with catalytic converters. EPA banned the use of leaded gasoline in highway vehicles in December 1995 (EPA 2006a). As a result of EPA's regulatory efforts to remove lead from gasoline, emissions of lead from the transportation sector have declined dramatically(95%between 1980 and 1999), and levels of lead in the air decreased by 94% between 1980 and 1999. Transportation sources,primarily airplanes,now contribute only 13%of lead emissions. A National Health and Nutrition Examination Survey reported a 78%decrease in the levels of lead in people's blood between 1976 and 1991. This dramatic decline can be attributed to the move from leaded to unleaded gasoline (EPA 2006a). The decrease in lead emissions and ambient lead concentrations over the past 25 years is California's most dramatic success story with regard to air quality management. The rapid decrease in lead concentrations can be attributed primarily to phasing out the lead in gasoline. This phase-out began during the 1970s, and subsequent California Air Resources Board(ARB)regulations have virtually eliminated all lead from gasoline now sold in Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.3-5 Air Quality