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i AIR QUALITY STANDARDS Ambient air quality is described in terms of compliance with state and national standards. Ambient air quality standards are the levels of air pollutant concentration considered safe to protect the public health and welfare. They are designed to protect people most sensitive to respiratory distress, such as asthmatics, the elderly, very young children, 'i people already weakened by other disease or illness, and persons engaged in strenuous 'I work or exercise. National Ambient Air Quality Standards (NAAQS) were established by the EPA in 1971 for six air pollution constituents. States have the option to add other pollutants, to require more stringent compliance, or to include different exposure periods. �� California Ambient Air Quality Standards (CAAQS) and NAAQS are listed in Table 4.5-1. !I Air Quality Monitoring Figure 4.5-1 depicts the air quality monitoring station locations in the Basin. Ambient air quality data for the project area was obtained from monitoring stations operated by the SJVUAPCD, which are closest to the project site. Table 4.5-2 presents a summary of the air quality data obtained from the Stockton (Hazelton) monitoring station, which offers I gaseous and articulate monitoring; and the Trac monitoring station which offers gaseous P g Y 9 9 j� pollutant monitoring. As indicated, some exceedances of state standards for 03 and PM,o occurred between the years 1991 and 1995. Based on data obtained from the Stockton it (Hazelton) monitoring station, the state 03 standard was exceeded an average of eight days per year; the federal 03 standard was exceeded twice; and the state and federal CO 8-hour standards were each exceeded once during this period. In addition, the state PM,o r standard was exceeded in approximately 24% of the samples taken at the Stockton ,9 (Hazelton) monitoring station over the five-year period. The federal standard was not t .I exceeded during this time. Data obtained from the Tracy monitoring station is considered "...valid but incomplete in that an insufficient number of data points were collected to meet I^{ EPA and/or CARB criteria for representativeness" (CARB, 1995). Meteorological Influences on Air Quality i Regional flow-patterns-have an,effect on air quality patterns by directing pollutants downwind of sources. Localized meteorological conditions, such as light winds and it shallow vertical mixing; and topographical features, such as surrounding mountain ranges, create areas of high pollutant concentrations by hindering dispersal. An inversion layer is produced when a layer of warm air traps cooler air close to the ground. Such temperature F' inversions hamper dispersion by creating a ceiling that traps air pollutants near the ground (SJVUAPCD, 1992). Draft Environmental Impact Report 4-63 ER-96-3 !i