STONE DEGRADATION DUE TO WET DEPOSITION OF POLLUTANTS

As part of an overall programme of study upon the action of atmospheri c pollutants on building stones, the degradation of limestones has bee n measured by dissolution in various solutions with different anions, in simulation of attack by wet deposition of salts found in acid rain. In water, CO2 plays a significant role in increasing material losses from limestone. Solution volume and permitted reaction time are also i mportant factors. With pH decrease the CO2 role becomes less significa nt and the calcium entering solution is then controlled by the polluta nt (acid)/stone(base) reaction. In neutral salt solutions reactions ar e determined by the buffering capacity of the solution, limited by sol ubility criteria, and modified by common ion effects (reducing solubil ity) and by shielding ions (increasing solubility). Ammonium salts hav e an intermediate position but act predominantly through the pH effect .