According to a new Canadian study, natural sunlight triggers the release of smog-forming nitrogen oxide compounds from the grime that typically coats buildings, statues and other outdoor surfaces in urban areas.
The researchers, who reported their findings in the annual conference of the American Chemical Society being held in Boston (16-20 August), carried out the tests in terraces in Germany recording the "behavior" of ... Smudge both in bright light sun and shade.
In a previous study, Dr. Donaldson had already found in the laboratory that the artificial sunlight was able to release nitrogen components from the so called ‘blackness’ of cities, which comprises a mixing of chemicals from the exhausts of vehicles and chimneys.
In his latest study, in collaboration with colleagues from Leipzig, Dr. Donaldson decided to transfer his experiments on building terraces. In a tall tower of the town, researchers placed two large shelves filled with glass beads. One of the two shelves was located at a point where it could accept the sunlight during the day, while the other was in the shade. Soon all the beads began to acquire a gray, dusty appearance.
James Donaldson said “The current understanding of urban air pollution does not include the recycling of nitrogen oxides and potentially other compounds from building surfaces. But based on our field studies in a real-world environment, this is happening. We don’t know yet to what extent this is occurring, but it may be quite a significant, and unaccounted for, contributor to air pollution in cities.”
The researchers said that the grime in shaded areas contained 10 percent more nitrates than grime exposed to natural sunlight, which was consistent with the team’s laboratory findings.
This percentage may seem little, but experts believe that as the sunlight triggers the release of smog-forming nitrogen oxide, a new coating that is rich in harmful substances is created.