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4.5 AIR QUALITY ENVIRONMENTAL SETTING Air Basin Characteristics The project is located within the San Joaquin Valley air basin. This air basin is a well-defined climatic region, primarily because of the topographic barriers forming distinct boundaries on three sides of the basin. The western boundary is formed by the Coast Range, the southern boundary by the Tehachapi Mountains, and the eastern boundary by the Sierra Nevada. Only the northern boundary is not marked by a distinct topographic feature. In the northern portion of the basin, the Carquinez Strait, a sea-level gap between the Coast Ranges, extends to the west and is a major source of ventilation for the basin. Winds measured at Stockton (the closest location with long-term wind records) show a strong dominance of west to northwesterly winds (California Department of Water Resources, 1978). Wind speeds are generally highest during the spring months and lightest in the fall and winter. Air Quality Standards and Pollutant Characteristics The Mulford-Carrell Act of 1969 and the Clean Air Act of 1970 established state and federal air quality standards for several pollutants. These standards are divided into primary standards, designed to protect the public health, and secondary standards, intended to protect the public welfare from effects such as visibility reduction, soiling, nuisance, and other forms of damage. The state and federal standards are summarized in Table 4.5-1. The State of California and the federal ambient air quality standards differ. In particular, the state standards for ozone, carbon monoxide (1-hour standard) and PM-10 are considerably more stringent than the federal standards. Not all of the pollutants shown in Table 4.5-1 are problems in San Joaquin County. The standards are generally met except for ozone, PM-10 and, in the Stockton area, carbon monoxide. The characteristics and sources of these pollutants are described below. 4.5-1