Cleaner Air to Turn Iconic Buildings Green

The Pentagon and other icons are going green… but not in the way you may think.

ByABC News
December 4, 2008, 6:52 PM

Dec. 5, 2008— -- For buildings the future is bright - bright green, that is. New research into how stone facades will be altered by changes in the atmosphere suggests that the days of smutty grey and black buildings are gone.

The coming century will see iconic limestone structures like the Empire State Building, the Pentagon, and the gothic cathedrals of Europe and the US turn yellow, reddish-brown, and even green with lichen and moss.

Cities will become more colourful as pollution patterns change and wind-swept rain washes away the black coal soot typical of the 20th century. What's more, legal requirements to use clean fuels are likely to mean lichens and mosses will grow more easily, turning buildings green in parts.

In the 19th and 20th centuries, cities in Europe and the US were dominated by dark grey and black buildings. These were often made of cream-coloured stones like limestones, covered in a black crust of coal soot. According to Peter Brimblecombe and Carlotta Grossi of the University of East Anglia in the UK, the era where atmospheric pollution determined the damage to building materials is over.

The pair recently completed an assessment of how damage to buildings in London has varied over the past 900 years and how it is likely to evolve over the coming century - when soot from coal-burning stoves is unlikely to be a concern, but climate change is.

They used historical climate and pollution data, combined with equations that describe how different climates and different types of pollution affect building materials. For instance, archive tax records show how much fuel was used through the centuries, which can be used to estimate historical pollution levels.

Sooty Anomaly

With estimates of how much black carbon soot deposited on buildings at different times, the researchers can calculate the reflectivity of buildings, which indicates how black they were. It turns out that for most of the 900 years, buildings were clean.

"It seems the past two centuries [of blackened buildings] were a bizarre anomaly," says Brimblecombe. "In a sense, we are now back in medieval England."