Galvanized steel samples were exposed for periods of up to 30 months at nine air monitoring sites in the St. Louis, Missouri area. Climatic and air quality data were recorded during the exposure periods and were subjected to a rigorous evaluation to eliminate recording errors and to estimate missing values. Weight loss was used as the measure of zinc corrosion on the galvanized steel. Corrosion rate was 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 were evaluated to determine the most likely 'critical relative humidity'. A theoretical model of film buildup and dissolution was developed to explain how factors affect corrosion rates. Non-linear and linear multiple regression techniques were used to determine the statistical significance of each factor.