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Long-term weathering studies on St. Paul's Cathedral, London

Long-term weathering studies on St. Paul's Cathedral, London

This project concerns the work of a research term monitoring the rate of surface loss of the stone at this site since 1980. The latest survey showed that during that time weathering has decreased in proportion to the decreasing SO2 in the atmosphere; (see: Trudgill, S. T., Viles, H.A., Inkpen, R., Moses, C., Gosling, W., Yates, T., Collier, P., Smith, D.I and Cooke, R.U., 2001. Twenty-year weathering remeasurements at St Paul's Cathedral, London. Earth Surface Processes and Landforms, 26 (10): 1129-1142). In 2000 the data were replicated using a second micro-erosion meter held by Dr. Robert Inkpen, Department of Geography, University of Portsmouth; contact: The next re- measurement is scheduled for 2010.

  • Measurements show that the rates of weathering on St. Paul's Cathedral, London have halved in the last ten years (1990 - 2000) as compared with the previous ten years (1980 - 1990).
  • Yearly averages of sulphur dioxide concentrations in the air decreased from around 25 parts per billion (ppb) in the early 1980's to 10 ppb in 1990-2000.
  • Battersea Power Station, upwind in the direction of the prevailing wind, closed in 1983.

In the 1980-1990 period, repeated micrometer measurements accurate to three decimal places showed that the stone surface of the balustrade surrounding the upper level of the Cathedral was losing an average of 0.045 mm a year. In 1980-1982, air pollution, as measured by the yearly average concentration of sulphur dioxide in the air, was high at 20-25 parts per billion (ppb) in Central London. The Cathedral also showed especially high rates of stone loss in the south-west corner (up to 0.3 mm between 1980 and 1981, about ten times the average for the rest of the Cathedral) which was facing, and down wind from, Battersea Power Station. However, Battersea Power Station closed on October 31st 1983 and the general air pollution levels also decreased to an average 10 ppb in 1990-2000. The 1990-2000 average annual rate, calculated from measurements repeated in May 2000, is now half the 1980-1990 rate at 0.024 mm a year.

St Paul's Cathedral
St Paul's Cathedral (Public domain image from Wikipedia)

Since May 2000, the research team have been checking their measurement instruments, procedures and details of the data as well as the variations around the Cathedral which will be presented at the conference. Clearly, the procedure involves micrometer measurements of very small changes and so they have been cautious about the reliability of measurements and their susceptibility to factors like the temperature at the time of measurement. The net outcome of the tests is that while the measurements are actually taken to 0.0001 mm, the researchers feel that the change from 0.045 mm per year (0.45 mm 1980-1990) to 0.024 mm a year (0.24 mm 1990-2000) can be reliably reported.

This means that air pollution control in London appears to be benefiting buildings. However, the team believe that complacency would not be an appropriate reaction: there is evidence of some 'crusting' or deposition at some sites which could yet still be easily eroded and the rates for St. Paul's are still higher than rates measured for some non-urban sites.