Galvanized steel samples are exposed for periods of up to 30 months at nine air monitoring sites in the St. Louis, MO area. Climatic and air quality data are recorded during the exposure periods and subjected to a rigorous evaluation to eliminate recording errors and to estimate missing values. Weight loss is used as the measure of zinc corrosion on the galvanized steel. The corrosion rate is evaluated with respect to (1) fluxes of pollutants (sulfur oxides, nitrogen oxides, oxidants, and particles) to the galvanized steel during both wet and dry periods, (2) temperature, and (3) amount of rainfall at Lambert Field (airport). Different definitions of when the galvanized steel was wet are evaluated to determine the most likely “critical relative humidity.” A theoretical model of film buildup and dissolution is developed to explain how factors affect corrosion rates. Nonlinear and linear multiple regression techniques are used to determine the statistical significance of each factor.