The results of thirty months of environmental exposure of marble samples at nine air monitoring sites in the area of St. Louis, Missouri, have been evaluated. The marble erosion data were evaluated with respect to the possible effects of time-of-wetness, wind speed, temperature, and levels of total gaseous sulfur compounds, total gaseous oxides of nitrogen, and oxidants. In an empirical relationship, time-of-wetness was the only statistically significant factor, accounting for 98.74% of the marble deterioration variability.