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III. Environmental Setting, Impacts,and Mitigations G. AIR QUALITY SETTING Climate/Meteorology The rim factors which determine air quality are the locations of air pollutant sources and the primary q Y amounts of pollutants emitted. Meteorological and topographical conditions,however,also are important. Atmospheric conditions such as wind speed,wind direction, and air temperature gradients interact with the physical features of the landscape to determine the movement and dispersal of air pollutants. The project site is in San Joaquin County,which is part of the eight-County San Joaquin Valley Air Basin. The Valley is relatively flat,bordered by mountains to the east, west and south. This topographical configuration tends to inhibit air circulation and hence air pollutant dispersion. The climate of the Central Valley is characterized by hot,dry summers and cool,rainy winters (California Air Resources Board, 1975). During the winter,the North Pacific storm track intermittently dominates weather in the air basins. Fair weather alternates with periods of extensive clouds and precipitation. Periods of dense and persistent low-level fog,prevalent between storms,are characteristic of winter weather. These conditions result in stagnant atmospheric conditions that may last for weeks at a time. The frequency and persistence of heavy fog in the Central Valley diminishes with the approach of spring, when the days lengthen and the intensity of the sun's rays increase. During the summer,the valley becomes nearly isolated from the storm track, and cool marine air enters through the Carquinez Strait and the Cordelia Gap in the Coastal Ranges. Air enters the Valley through the Carquinez Strait, moving across the Delta and flowing into the Air Basin, bringing with it pollutants from the heavily populated San Francisco Bay Area. Some transport of air pollutants also occur from the Sacramento region. From May to October,the region's intense heat and sunlight lead to high ozone(03)concentrations. Wind direction determines the direction air pollutants are transported,and wind speeds determine the amount of air available for dilution of air pollution emissions. In the San Joaquin Valley, winds generally blow from the north. Predominant winds,at the Stockton monitoring station, about 30 miles to the northwest of Austin Road Landfill,are from the west northwest(about III.G.1