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Background Information Report

Air Quality

The existing air quality of the affected environment is defined by air quality data which are obtained by examining records from air quality monitoring stations maintained by the TNRCC, formerly the Texas Air Control Board (TACB). Information on pollutant concentrations measured for short-term (24 hours or less) and long-term (quarterly and annual) averaging periods is extracted from the monitoring station data in order to characterize the existing background air quality of the area. Air quality in a region is determined by comparing the ambient concentration of specific pollutants with the appropriate federal, state, and local ambient air quality standards. Ambient air quality standards are maximum limits or concentrations of pollutants in air. Federal standards are based on estimates of maximum concentrations that, with an allowance for safety, present no hazard to human health or the environment.

The Clean Air Act (CAA) provides the basis for regulating air pollution to the atmosphere. The CAA required the EPA to establish ambient ceilings for certain criteria pollutants. The ceilings were based on the latest scientific information regarding the effects a pollutant may have on public health or welfare. Subse­quently, the Unites States Environmental Protection Agency (EPA) promulgated regulations that set national ambient air quality stan­dards (NAAQS). NAAQS have been established for sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), ozone (O3), particulate matter equal to or less than 10 micrometers in diameter (PM-10), and lead (Pb). The State of Texas has adopted the NAAQS.

According to EPA guidelines, an area with air quality better than the NAAQS for a specific pollutant is designated as being in attainment for that pollutant. Any area not meeting ambient air quality standards is classified as nonattainment for the pollutant on which the standard has been exceeded. When there is a lack of data for the EPA to define an area, the area is designated as unclassified and is treated as attainment until proven otherwise. CSSA is located within the Metropolitan San Antonio Intrastate Air Quality Control Region (AQCR) 217. This AQCR is classified by EPA as a near nonattainment area (TNRCC, 1998).

Ambient air quality monitoring conducted by TNRCC in San Antonio is limited to four of the criteria pollutants: PM-10, CO, O3, and Pb. During 1991, no ambient air quality standards were exceeded (TACB, 1991a; TACB, 1991b; EPA, 1992a) at the six ambient air monitoring stations which were in operation.