Soiling of limestone in an urban environment characterized by heavy vehicular exhaust emissions

The inorganic and organic chemical composition of weathering sulphate patinas on the limestone walls of Emmanuel College, Cambridge, UK, have been analysed by FT-IR spectroscopy, pyrolysis gas-chromatography/mass spectrometry and scanning electron microscopy. The College location is characterized by heavy vehicular exhaust emissions including those from diesel powered public transport vehicles due to its proximity to the main Cambridge coach station. A complex mixture of gaseous and particulate air pollutants are found deposited in the weathering patinas including organic compounds (such as PAHs), which represent markers for present-day vehicular pollution. Slight differences in composition between patinas collected at different heights on the building facades with, in particular, more evidence for a biogenic overprint in samples collected at roof level as opposed to ground (street) level are found. Analytical results confirm how building stones in urban areas acted in the past and still do today as passive repositories for any kind of gaseous and particulate air pollutant present in the surrounding atmosphere; accordingly, weathering patinas are slowly changing their composition to accommodate new classes of present-day air pollutants.