SCOPE AND STATUS OF PROGRAM The overall program consists of three distinct phases involving field sampling@ aerosol analyses@ and statistical and interpretive analyses. Work performed during this report period was limited to the first two phases. Field sampling was conducted in downtown Columbus during the latter half of July@ 1972@ in New York City (Welfare Island) throughout August@ and in Pomona@ California@ for 10 days in mid-November. The sampling involved continuous monitoring of the meteorological conditions and the gas-phase composition of the air (including CO@ NO@ NO2@ SO2@ ozone@ methane@ ethylene@ acetylene@ and total hydrocarbon) concomitant with collecting aerosols and measuring visibility reduction due to light scattering. All aerosol samples were collected on a diurnal basis. To provide the aerosol mass needed for organic analyses@ three samplers operated continuously at 20 cfm@ sampling 25 feet above ground level. Because this project is devoted to small particles which cause light scattering@ the samplers were equipped with size-fractionating devices which provided particle separation (based on aerodynamic size) near 2 ?? diameter. An analytical scheme was developed for determining the organic features of aerosols. In addition to providing qualitative information concerning the broad chemical classes and functional groups present in the organic fraction of aerosols@ the scheme provides numerical data. thereby permitting statistical treatment of organic compositional data together with data on air quality and inorganic composition. Numerical organic data describe the weight-percent solvent extractable (methylene chloride and dioxane) components of the aerosols@ weight-percent CHN in the extractables@ infrared spectroscopic band intensities for specified absorptions@ aromatic/aliphatic ratios (by NMR) and quantitative functional group analyses for total alcohol and total carbonyl in specified sample fractions. The scheme has been applied to six aerosol samples; two diurnal samples collected at each of the three sampling sites. Inorganic analyses were performed on aerosols selected from 22 of the 43 sampling days at the three sites. The analyses included trace metals by optical emission spectrometry@ CI@ Br@ S@ and Pb by X-ray fluorescence@ and SO4@ NO3@ NH4@ and CHN by other chemical methods. The third year of this program will initially be devoted to two activities: (1) detailed interpretation and modeling of the ambient air-quality data and aerosol analytical results currently available and (2) application of the organic analysis scheme to aerosols generated photochemically from auto exhaust. Depending on the outcome of these tasks@ the completion of the third-year program will involve investigations among the following activities; (1) additional field sampling@ (2) additional chemical analyses of aerosols from previous sites and/or a new site@ and (3) a statistical analysis of the air quality and compositional data to identify relationships between aerosols and their sources.