This paper describes atmospheric corrosion tests on five alloys and two coated steel products at five sites as part of the National Acid Precipitation Assessment Program. Tests were conducted on samples boldly exposed to the atmosphere, sheltered from the atmosphere, and facing skyward and groundward. Details of the corrosion process related to orientation and sheltering and involving particulates, corrosion film chemistry and morphology, and the dissolution- reprecipitation process were established. The corrosion film on zinc was found to saturate with sulfur at approx. 7 Wt% with increasing ambient sulfur dioxide concentration. Zinc corrosion on the skyward side appeared to be cathodically protected in two-sided bold exposures. Only large particulates were found on the surface of sheltered copper and zinc, and small particulates dissolved and dispersed into the corrosion film. The dissolution-reprecipitation process occurred primarily during the final stages of drying.