Sussex University lecturer Cherith Moses reckons that one of Britain’s most iconic buildings could turn green because pollution levels have fallen so much.
Dr Moses, a senior lecturer in physical geography, is part of a team that has been studying the effects of pollution on St Paul’s Cathedral.
The team found that the London landmark was safer from pollution eroding its limestone façade than it has been at any time since it was built 300 years ago.
Levels of sulphur dioxide, which is responsible for acid rain, have fallen by 95 per cent over the past 30 years.
The fall has been attributed mainly to a decrease in industry and power generation in central London and the capital increasingly moving to cleaner energy.
Acid rain is now responsible for a fraction of 1 per cent of the damage to St Paul’s. And the rate of erosion at the cathedral is now dominated by natural rainfall, which is a weak carbonic acid with a pH of about 5.6.
The researchers – from Sussex, Portsmouth, Oxford and Cambridge universities – conducted the longest-ever study of erosion rates on a single building.
They monitored the rate of erosion on the balustrade between 1980 and 2010 using a micro erosion meter to take periodic readings of pollutants in the natural stone.
St Paul’s has survived the ravages of the Industrial Revolution, the nearby Bankside Power Station’s plumes of sulphur dioxide gas and smoke and Londoners’ love of coal fires.
The team’s findings are published in the journal Atmospheric Environment. The scientists found atmospheric sulphur dioxide concentrations fell from a daily average of 80 parts per billion (ppb) in the early 1980s to less than 3ppb by the late 2000s.
They are now trying to see whether natural organisms that might no longer be retarded by pollution or aggressive erosion could in future colonise natural stone buildings like St Paul’s. If so, this could pose a new erosion risk.
Dr Moses, who is an expert in limestone weathering processes and products, said: “With predicted changes in rainfall linked to climate change, our research findings make it even more important for us to understand whether microflora, including algae, lichens and micro-organisms, erode or protect stone surfaces.
“Natural stone buildings, under predicted wetter conditions, may be become ‘greener’ in the future because of microfloral colonisation.
“Our research will continue to investigate this over the next ten-year measurement period.”
The unique dataset collected by the team may provide more effective predictions for building conservation projects.
It may also provide valuable analyses for other major natural stone buildings such as St Peter’s Church in Brighton.
The researchers have continued studying erosion and surface change rates at St Paul’s and will report their next findings in 2020.
It is great to know that acid rain rapidly decreased and pollution levels were minimized. It is significant that we adapt changes that will be beneficial not only to us but to historic landmarks too.