REACTIONS OF GASES ON CALCAREOUS STONES UNDER DRY CONDITIONS IN-FIELDAND LABORATORY STUDIES

Dry deposition of gases plays an important role for the deterioration of stone materials and a better understanding of the processes involve d will improve our ability to maintain stone monuments and buildings. As a part of an EU-project an investigation with four calcareous stone types have been exposed outdoor at two test sites in Norway for two y ears. The exposure has been carried out in sheltered position and the amount of reaction products and the penetration depth of SO2 into the stones was determined as soluble sulphate after half a year and after one and two years. Even if most of the sulphate was found in the upper 0.3 mm of the stone, there was an increase in the sulphate content in stone even down to the center of the stone sample. In laboratory test s with SO2, NO2 and changing relative humidity the synergistic effect of NO2 and the importance of the relative humidity was investigated. T he uptake rates were calculated from the laboratory studies by analyzi ng the gas concentrations before and after the exposure chamber. By ca lculating the deposition velocity from the field study by using the am ount of sulphate found in the stones together with the average outdoor concentration of SO2 at the test sites, the values were a magnitude h igher than in the laboratory test, highest at the industrial paper mil l sites with high concentrations both of SO2 and some hypochlorite and lower in urban atmosphere with fairly low values of SO2 and high valu es of NO2.