The program consisted of three distinct phases involving analytical methods development, field studies, and analysis and interpretation of the field study results. The analytical development phase of the program involved developing or refining state-of-the-art techniques for the determination of ambient levels of PAN, NH3, and NH4(+). The field sampling phase of the program consisted of five weeks of air monitoring and particulate collections in St. Louis, MO. and West Covina, CA. In addition, NO, NO2, O3, NO2(-), NO3(-) and C, H, N were determined. Meteorological variables including wind speed, wind direction, temperature, relative humidity and solar intensity were also monitored continuously. In St Louis, several rainfall samples were collected and analyzed for trace nitrogen compounds. Composite dust samples were collected in both cities and analyzed for nitrogen constituents. Silver-membrane filter samples were also taken in West Covina for analysis by electron spectroscopy chemical analysis.