Weathering of materials at Notre-Dame from changes in air pollution and climate in Paris, 1325–2090

Abstract

Notre-Dame, as with much historic architecture in Paris, has been exposed to the ravages of changing pollution and climate. Estimates of historic temperature, precipitation and relative humidity and concentrations of key atmospheric pollutants SO2 NO2, O3 and PM10 have been combined with projections under Intergovernmental Panel on Climate Change scenarios RCP2.6 and RCP8.5 to estimate long term soiling, recession and corrosion. The Lipfert function and dose response equations from the International Co-operative Programme on Effects on Materials were used to estimate long-term damage. The picture reveals that the effect of pollution is apparent from around 1700, though it increases notably after 1850; then most pollutant concentrations decreased through the latter half of the 20th century. The soiling predicted for sheltered surfaces follows this trend, although changes in wind direction and washing by rain can also alter the dark and light patterns. Buildings facades are likely to be cleaner over the present century, so we may well be sensitised to other changes that architectural surfaces undergo, e.g. changing patterns and forms of biological growth and parallel changes in colour, especially if surfaces remain wet for substantial periods. In the coming century, decreasing snow fall and longer times of wetness could enhance recession and corrosion rates. While metals in general are likely to corrode less in future compared to the 20th century, some such as copper would be sensitive to any increases in ozone concentrations. Lead used as new roofing for Notre-Dame can be mobilised, increasing heavy metal concentrations in the local environment.