At the conference of the American Chemical Society in Boston, Massachusetts, findings show that grime attached to urban buildings will ‘exhale’ toxic gasses when they come into contact with sunlight.

After experiments were conducted in Germany, which looked at the state of grime that had exposure to sunlight and grim that had little to no exposure, researchers found that the grime that bathed in the sunlight has a way of absorbing certain gases from the atmosphere, which combined with the nitrogen that the grime releases over time, releases nitrogen dioxide (NO2), a toxic pollutant that contributes to the formation of smog.

James Donaldson, a chemistry professor with the University of Toronto in Canada, led the research after spending most of his research time inside of labs. After working with other experts in Leipzig, Germany, where the experiment was set up, new light was shed on things, so to speak.

“Rather than being a permanent sink for nitrogen oxide gases…grime exposed to sunlight can re-release some of these gases back into the urban atmosphere,” said James.

Although the experiment only showed a loss of 10% of the nitrogen present inside of the grime, it should not come as a surprise that this shouldn’t go on unfettered.

The lost nitrogen, with the grime constantly re-exposed to the sunlight, gets reabsorbed into the grime. This leads to a steady state of variation.

“In our lab experiments, what we did was take a full bathtub and pull out the plug,” Professor Donaldson explained. “In the field experiment, we opened the plug but left the water running.”