general discussion of atmospheric processes and an evaluation of source-receptor analyses incorporated into past regulatory-effect analyses; this will improve understanding of the geographic locations in which changes in emissions might be important from a public-health perspective. Descriptions of the collection and processing of data are incorporated by reference to our interim report.

REVIEW OF PAST FINDINGS

In our interim report, we examined the criteria pollutants—carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), lead (Pb), ozone (O3), particulate matter (PM10 and PM2.5) that are regulated under the National Ambient Air Quality Standards (NAAQS) (Table 2-1) and to which NSR applies. It was found that NO2 and SO2 NAAQS have not been exceeded in any monitored part of the United States for more than 10 years, although some of these areas have not yet been designated as officially in attainment. CO exceedances were found at a few neighborhood-scale locations (Chow et al. 2002) near roadways and were clearly attributable to mobile-source emissions not subject to NSR. Pb nonattainment areas in Missouri and Montana are near lead-production facilities that are currently subject to emission-reduction efforts. High CO concentrations were usually exacerbated by local topographic and meteorologic characteristics. PM10 nonattainment areas were found mostly in the western states, in many cases owing to wintertime residential woodburning, fugitive dust, or nearby industrial sources (usually fugitive dust from material handling or uncontrolled ducted emissions). Exceptions were California’s South Coast Air Basin (Los Angeles area) and central valley, where fall and wintertime PM10 exceedances were driven by high PM2.5 nitrate and carbon components. Many of the PM10 nonattainment areas have implemented appropriate control measures, and PM10 levels have been reduced (EPA 2004h).

PM2.5 and O3 are the criteria pollutants with the most geographic areas in nonattainment. In addition, in summarizing the health effects of criteria air pollutants, we found the most substantial evidence of health effects in connection with current atmospheric concentrations of PM2.5 and O3. Thus, from a public-health perspective, PM2.5 and O3 have the most important effects attributed to changes in NSR.

Ambient O3 and much of the PM2.5 are not directly emitted but form through atmospheric reactions of directly emitted volatile organic compounds (VOCs), NOx (sum of nitric oxide [NO] and NO2, expressed as NO2 in emission inventories), and SO2 (Pandis 2004). Sulfates, nitrates, and some of the organic carbon found in PM2.5 are termed secondary aerosol, owing to their formation from emitted gases, as opposed to directly emitted PM,



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