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 (SOb2s). The results of the analysis show that both TSP and SOb2s 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 percent while SOb2s concentrations have shown a much greater improvement, decreasing by approximately 50 percent. These improvements in air quality have primarily resulted from the increased use of cleaner-burning fuels in the residential, commercial, and industrial sectors of most urban areas. Local and State air pollution regulations limiting the use of coal and high-sulfur fuels have resulted in creased use of low-sulfur oil and natural gas as the primary sources of energy. These results are preliminary and will be further developed as State air quality information is included in the trends evaluation.