RATE OF WEATHERING OF MARBLE DUE TO DRY DEPOSITION OF AMBIENT SULFUR AND NITROGEN DIOXIDES

The thickness of crust upon marble is a measure of weathering due to d ry deposition of pollutants in industrial environments. We monitored t he rate of growth of crust upon marble due to the reaction of ambient SO2 and NO2 with samples exposed outdoors but protected from rain. Eve n when the atmospheric NO2 exceeded the SO2, the reaction product calc ium sulfate exceeded calcium nitrate, indicating the predominance of S O2 in marble decay. This result is consistent with a study of monument s in cemeteries in the Los Angeles basin, where the NO2 concentration has long been larger than the SO2 concentration. The kinetic rate cons tant and the diffusion coefficient were obtained from a model equation as being 395 cm/h and 0.13 cm(2)/h, respectively. These constants all ow the prediction of crust thickness in a wide range of SO2 and NO2 co ncentrations.