patterns and trends in levels of suspended particulate matter

Abstract

The National Air Surveillance Network (NASN) has collected samples of suspended particulate matter since 1957. These data values are graphically summarized by the application of Whittaker-Henderson Type A curve-smoothing formulas to 10 years of data. Fifty-eight urban sites and 20 nonurban sites are studied by this technique, which permits an intuitive grasp of the underlying cyclical patterns as well as long-term trends in nationwide levels of suspended particulate matter. Seasonal patterns are evident for many urban and nonurban sites, although sharp contrasts in seasonal characteristics exist between the two types of sites. Long-term levels tend slightly downward at many urban locations, but the opposite effect is observed at many nonurban sites.