The huge air pollution generated by the Industrial Revolution led to the formation of acid rain. And every drop that fell on St Paul’s Cathedral caused microscopic damage to its limestone structure.
Now work by our own Dr Robert Inkpen, Principal Lecturer in Physical Geography, hopes to safeguard such historic buildings by studying how pollution has changed them over time.
Dr Inkpen said: ‘For conservators looking after such historic buildings, it’s vital to understand the nature of the damage they've experienced and how it relates to past levels of air pollution. Historic buildings are susceptible to erosion by acid in rain because many of them, St Paul’s included, are made of limestone.'
In monitoring St Paul’s, Dr Inkpen and his colleagues have been able to measure sulphur dioxide levels directly. But in pursuit of historic data from further back, researchers turned to another source: marble gravestones across England and Wales.
Historic pollution levels could help us understand the effectiveness of environmental regulation in relation to public health. And in turn, this could help predict the potential impact of increasing urbanisation
Particularly prized for its quality, it has been mined since the days of ancient Rome. Such gravestones typically have the details of the deceased person chiselled out of the rock. Lead is then inlaid and polished until the surface is smooth.
Over time, the marble - limestone exposed to extreme heat and pressure - is eroded by acidic rainwater, while the lead lettering remains untouched. By using the date details on the gravestone, researchers can then measure how much of the original marble has gone, and over what period of time.
And by using specialised engineering callipers, they can measure the depth of erosion to a precision of 0.01mm – or half the width of the finest human hair. From these figures, Dr Inkpen and colleagues can then estimate the levels of historic air pollution the stone has experienced, taking into account a host of local variables.
The information offers significant help to those protecting the future of Britain’s landmarks, but it could have another use too – given the many diseases associated with air pollution, Dr Inkpen's findings could even help to safeguard human health.