AbstractThe influence of tetraethoxysilane (TEOS) or alkyltriethoxysilane (ATEOS) impregnation on the deposition of sulphur dioxide (SO2) on sandstone and limestone exposed to moist air containing SO2 in the sub-ppm range, with or without nitrogen dioxide (NO2), was investigated under controlled conditions. The silane treatinents reduced the deposition of SO2 on both sandstone and limestone. This reduction was less pronounced when SO2 and NO2 were present simultaneously. The order of the SO2 deposition was: untreated > TEOS > ATEOS. The deposition rate of SO2 was enhanced by the presence of NO2. When SO2 was the only pollutanl present, the samples contained sulphur(IV) in the form of CaSO3·0·5H2O, whereas samples exposed to SO2 + NO2 contained sulphur(VI) in the form of CaSO4·2H2O (gypsum).
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