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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures _ Development Department Air Quality Physical Setting Regional Climate and Meteorology — The area's climate is characterized by warm, dry summers and cool winters. Wind speed and direction data indicate summer winds usually originate at the north end of the SJVAB and flow in a south-southeasterly direction through the SJVAB and Tehachapi pass into the Mojave Desert Air Basin. During the winter,winds occasionally originate from the south end of the SJVAB and flow — in a north-northwesterly direction. The predominate winds in the project area blow from the northwest. The SJVAB has light,variable winds(less than 10 miles per hour[mph])during the winter months. Those low wind speeds, _ combined with low inversion layers in the winter,create a climate conducive to high concentrations of carbon monoxide(CO)and particulate matter less than 10 microns in diameter). The SJVAB's warm summers contribute to high _ concentrations of ozone. Criteria Pollutants and Local Air Quality Description of Pollutants The federal and state governments have established ambient air quality standards for six criteria pollutants: ozone,CO,nitrogen dioxide(NOA sulfur dioxide (SO2),particulate matter, and lead. Ozone,NO2, and particulate matter are generally considered to be "regional"pollutants,as these pollutants or their precursors affect air quality on a regional scale. Pollutants such as CO, SO2, lead,and particulate matter are considered to be local pollutants that tend to accumulate in the air locally. Particulate matter is considered to be a localized pollutant as well as a regional pollutant. In the area where the proposed Project is located,ozone,CO, and particulate matter are of particular concern. Brief descriptions of these pollutants are provided below. _ Ozone. Ozone is a respiratory irritant and an oxidant that increases susceptibility to respiratory infections. It can cause substantial damage to vegetation and other _ materials. Ozone is a severe eye,nose, and throat irritant. Ozone also attacks synthetic rubber,textiles,plants, and other materials. Ozone causes extensive damage to plants by leaf discoloration and cell damage. Ozone is not emitted directly into the air,but is formed by a photochemical reaction in the atmosphere. Ozone precursors,which include reactive organic gases(ROG)and oxides of nitrogen(NOx),react in the atmosphere in the presence of sunlight to form ozone. Because photochemical reaction rates depend on the intensity of ultraviolet light and air temperature,ozone is primarily a summer air pollution problem. The ozone precursors,ROG and NOx, are emitted by mobile sources and by stationary combustion equipment. State and federal standards for ozone have been set for an 8-hour averaging time. The state 8-hour standard is 0.07 parts per million(ppm), not to be exceeded, DeSilva Gates Quarry Project Draft Environmental Impact Report 3.0-2 J8s 05105 05