ARCHIVED REPORTS_1993_1 - Laserfiche WebLink

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1 1 1 1 1 1 1 1 1 1 1 1 1 .. -. _ _ __..._. _ _......__........ _. .._._.. .....__.__. __. ...... .__. .___ _ __ __ ___ ___ . . ................ .. _..... _._ _ .__. _..__.... ....................._._ _ _ ...... I ........ . I .. ...... ...... 4 7 A1R;QUALITY...... ENVIRONMENTAL SETTING Air Pollution Climatology The project site 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 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. The general windflow in the rest of the San Joaquin Valley is northwesterly most of the year, carrying pollutants from the northern portion of the valley towards the south. This general flow also transports pollutants from the Bay Area into the air basin. Air Quality Standards and Pollutant Characteristics The Mulford -Carrell Act of 1969 and the Clean Air Act Amendments 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 4.7.1. Not all of the pollutants shown in Table 4.7.1 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 problem pollutants are described below. Ozone Ozone is the most prevalent of a class of photochemical oxidants formed in the urban atmosphere. The creation of ozone is a result of complex chemical reactions between hydrocarbons and oxides of nitrogen in the presence of sunlight. Unlike other pollutants, ozone is not released directly into the atmosphere from any sources. The major sources of oxides of nitrogen and hydrocarbons, known as ozone precursors, are combustion sources such as factories and automobiles, and evaporation of solvents and fuels. The health effects of ozone are eye irritation and damage to lung tissues. Ozone also damages some materials, such as rubber, plants, and crops (Stern 1977). Ozone is the air pollutant that causes the most damage to agricultural crops in California. The most significant crop losses in California from ozone occur in the San Joaquin Valley (Thompson and Olszyk, 1988). Suspended Particulate Matter (PM -10) Suspended particulate matter consists of solid and liquid particles of dust, soot, aerosols and other matter, small enough to remain suspended in the air for a long period of time. A portion of the suspended particulate matter in the air is from natural sources such as wind blown dust and pollen. Man- made sources include combustion, automobiles, field burning, factories, and unpaved roads. Particulate matter also results from photochemical reactions in the atmosphere. ER -93-1 -83- (9-27-93)