Particulate matter concentration and air quality affected by windblown dust in the Columbia Plateau

The USEPA has proposed to regulate PMcoarse (particulate matter 2.5 to 10 mu m in diameter). Exceedance of the proposed National Ambient Air Quality Standard (NAAQS) for PMcoarse is expected within the Columbia Plateau of the Pacific Northwest United States based on the high frequency of dust storms and the large contribution of crustal material to fugitive dust in the region. The objective of this study was to explore the implication of the proposed NAAQS for PMcoarse on air quality. Concurrent observations of both PM10 (particulate matter <= 10 mu m in diameter) and PMfine (particulate matter <= 2.5 mu m in diameter) were made at Kennewick, WA from 1999 through 2005. Daily PMcourse concentration was determined as the difference between PM10 and PMfine concentrations. The number of exceedances of the proposed USEPA NAAQS for PMfine, was determined for various levels of the standard (the proposed daily level is 70 mu g m(-3)). Over the 7 yr of this study, the PM10 standard was exceeded on 16 d with PMfine constituting 4 to 7% of PM10. The proposed PMcoarse standard would have been exceeded on 35 d and represents a 120% increase in the number of exceedances over the current PM10 standard. Changing the level of the proposed PMcoarse standard to that of the current PM10 standard (150 mu g m(-3)) would result in a 20% decrease in the number of exceedances of the PM standard. The results of this study suggest that the proposed NAAQS for PMfine and PMcoarse will be exceeded more frequently than the current PMfine and PM10 standard in a region subject to seasonal dust storms.