Abstract |
Data collected through the National Air Surveillance Network for the past 12 years have been examined for trends in ambient levels of suspended particulates (TSP) and sulfur dioxide (SO2). The results of the analysis show that both TSP and SO2 concentrations at most center city NASN sites have declined significantly over the 12-year period. In general, stations with the highest concentrations in the early 1960's have shown the greatest improvement. The average center-city TSP concentration has decreased by approximately 20% while SO2 concentrations have shown a much greater improvement, decreasing by approximately 50%. |