New research suggests common city "grime" stores air pollutants and releases them when hit with sunlight.
According to BBC News, the researchers took to Germany to test how grime reacted to sunlight versus how it acted in the shade.
For the experiment, they placed two sets of window glass beads on a rooftop and covered one to simulate shade without blocking off the natural airflow. The beads exposed to sunlight apparently lost 10 percent more nitrate than those covered in shade.
The grime the researchers referred to was previously observed absorbing such pollutants, but the new study suggests it can be re-released. James Donaldson, a chemistry professor at the University of Toronto, led the study and presented the findings at the American Chemical Society's annual meeting in Boston.
He indicated the new study could help environmentalists better understand the various sources of air pollutants in urban settings by filling in a knowledge gap.
"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," he told reporters at the conference, according to BBC News. "The ones which were exposed to sunlight showed 10 percent less nitrate than the ones which were shaded, suggesting that there is a photochemical loss [of nitrogen] consistent with what we saw in the lab.
"In our lab experiments, what we did was take a full bathtub and pull out the plug," he said. "In the field experiment, we opened the plug but left the water running."
