Sunlight Causes Building Grime to Change into Dangerous Air Pollution

It turns out that the dirty coating that can be found on buildings and streets may be hazardous to public health. Scientists have discovered that the sun unleashes dangerous toxins from this grime into the environment.

When vehicles, power plants and other sources release compounds into the atmosphere, they become part of a reaction cycle that produces ground-level ozone. Some of this pollution actually leaves the atmosphere through chemical reactions, which produce nitrates, and wind up in the mix of thousands of different chemicals in urban grime.

"The current understanding of urban air pollution does not include the recycling of nitrogen oxides and potentially other compounds from building surfaces," said James Donaldson, a chemistry professor at the University of Toronto, in a statement.

In fact, sunlight and urban grime combine to create a previously unrecognized source of air pollution. The researchers found that with sunlight, gases are released; these gases are likely a combination of nitrogen dioxide and nitrous acid.

Nitrogen dioxide is toxic, and nitrous acid can help drive the production of ozone, which is the gas which causes photochemical smog in cities. In other words, neither of these gases are good news.

These findings show that it's important to note the effects of this grime in modeling. More specifically, it shows a source of pollution that should be targeted, especially since it can be harmful to human health. By targeting this type of pollution, researchers can reduce emissions and also improve health safety in cities.

The findings were presented at a conference of the American Chemical Society in Boston.

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