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III. ENVIRONMENTAL SETTING,IMPACTS AND MITIGATION MEASURES <br /> B. AIR QUALITY <br /> inversion. Air above and below an inversion does not mix because of differences in air density. <br /> y <br /> Inversions in the SJVAB can restrict air pollutant dispersal. <br /> REGULATORY FRAMEWORK <br /> Air quality is regulated through both national and state ambient air quality standards and through <br /> emissions limits on individual sources of air pollutants. Air pollutants can be grouped into three <br /> main categories,"criteria air pollutants,""toxic air contaminants,"and "odorous emissions,"each <br /> of which are discussed in more detail below. <br /> Criteria Air Pollutants <br /> Regulatory Context <br /> Under federal and state air quality laws,the U.S. Environmental Protection Agency (U.S. EPA) <br /> and the state Air Resources Board(ARB)have established national and state ambient air quality <br /> standards, respectively,for the most pervasive urban pollutants, including ozone,carbon <br /> monoxide,and particulate matter, among others. Table III.B-1 presents both sets of ambient air <br /> quality standards. An "ambient air quality standard"represents the level of air pollutant in the <br /> outdoor(ambient)air necessary to protect public health. Ambient standards do not apply to <br /> indoor environments. The federal Occupational Safety and Health Administration (OSHA) <br /> establishes standards for indoor workplace environments;these workplace air quality standards <br /> are substantially less stringent than the ambient air quality standards. U.S.EPA and ARB review <br /> the ambient air quality standards periodically in light of the results of on-going research. In 1997, <br /> U.S. EPA reaffirmed the national PM-10 standard and established a new standard for"fine" <br /> particulate matter(PM-2.5). U.S. EPA also established a new 8-hour ozone standard that will <br /> eventually replace the existing one-hour national ozone standard. <br /> Federal and state air quality laws require regions to be designated as"attainment"or <br /> "nonattainment"with respect to the national and state ambient air quality standards, respectively. <br /> The project site is located in Stockton in the San Joaquin Valley,a sub-region within the SJVAB. <br /> The SJVAB is currently designated as nonattainment for national and state ozone and PM-10 <br /> standards (SJVUAPCD, 1998a). The urbanized areas of Bakersfield,Fresno,Modesto,and <br /> Stockton were recently redesignated as "attainment"for the federal carbon monoxide standard. <br /> Because of the recent adoption of the PM-2.5 standard, and the lack of PM-2.5 data, the <br /> U.S. EPA has not made attainment classifications for any air basin in California(SJVUAPCD, <br /> 1998a). The SJVAB is attainment for the other ambient air quality standards. <br /> Federal and state air quality laws also require regions designated as nonattainment to prepare <br /> plans that either demonstrate how the region will attain the standard or that demonstrate <br /> reasonable improvement in air quality conditions. A series of air quality plans have been <br /> developed for the SJVAB. The following describes the most current federal and state air quality <br /> plans as they apply to the SJVAB: <br /> Stockton Scavenger Transfer Station Erpansion III.B.2 ESA 1990190 , <br />