Deterioration of Pentelic marble, Portland limestone and Baumberger sandstone in laboratory exposures to NO2: A comparison with exposures to gaseous HNO3

The effects of nitrogen dioxide on three calcareous stones (Pentelic marble, Portland limestone and Baumberger sandstone), used extensively in historic buildings, have been investigated under different conditions of relative humidity, mass of stone and grain size of stone. It was found that all three stones are not good sinks for NO2. Pentelic marble and Portland limestone exhibit relatively low vulnerability to NO2 and this does not vary with relative humidity significantly. The vulnerability of Baumberger sandstone, on the other hand, decreases with an increase in relative humidity and approaches those of Portland limestone and Pentelic marble at very high relative humidities. An expression has been derived enabling the comparison of the vulnerability of each stone to NO2 and gaseous HNO3. Assuming that the presence of other substances in the atmosphere of a city has a negligibly small effect on the validity of this expression it has been estimated that in Athens gaseous HNO3 is more corrosive than NO2 for marble monuments, in spite of its presence at appreciably lower concentrations. This conclusion can be generalized for all cities with a similar nature of air pollution.