Materials exposure sites, fully instrumented to characterize environmental parameters related to air quality, meteorology, and rain chemistry, have been established at four locations in the eastern and northeastern United States to study the effects of acid precipitation on atmospheric damage to metals, exterior paints, and building stone. A fifth, midwestern site has recently been added to the program. Utilizing short-term, seasonal, and long-term exposures, the corrosion behavior of five metal alloys (1010 carbon steel, Cor-Ten A, 3003-H14 aluminum, 110 copper, and 191 zinc) and two coated-steel products (galvanized steel and Galvalume) commonly used outdoors have been characterized using gravimetric, surface analytical, and corrosion film chemistry measurements. Monthly exposures indicate that the environments at the sites are significantly different in their effects on the metals.