Urban Grime emits nitrogen gases responsible for smog

In a new study, the scientists have said that the grime that clings to the buildings or any other structures is responsible for emitting nitrogen gases when hit by sunlight. This study contradicts the earlier assumptions made by the scientists where they assumed that the grime is harmless. This dark muck was known to absorb gases like these from the atmosphere but the study showed that the nitrogen does not stay locked away. The urban grime was thought to be inert but it was revealed that sunlight plays a key role in smog levels in cities. When the sunlight falls on this grime, the nitrogen based gases are released that eventually create the smog.

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For the study, the researchers tracked the content of grime in both sunlight and shade. The location chosen for the study was Germany. They found that the sunlit grime releases nitrogen in two forms: the toxic pollutant, nitrogen dioxide and the nitrous acid, which is a key ingredient of smog formation.

The first Photochemical smog was observed in 1950s and is yellow or black in color. It is a result of the chemical reaction that takes place between sunlight, nitrogen oxides and volatile organic compounds in the atmosphere which leaves the airborne particles and ground-level ozone.
The findings of the study were presented at a conference of the American Chemical society in Boston. Many of the pollution experts welcomed the study and agreed that this study could explain the missing part in the smog producing gas over the skies of London. The lead researcher, James Donaldson, a chemistry professor at the University of Toronto in Canada said,” 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.” Professor Donaldson has been working on this subject and some of his previous work has shown that artificial sunlight can strip the nitrogen component from the grime.

For the study, the researchers’ set up two large shelves filled with beads of window glass on a tower above the city. Both the shelves received the same air flow-but only one was in the sun. Donaldson told the reporters that the one that was exposed to sunlight showed 10 per cent less nitrate than the one that was shaded which suggested that there is a photochemical loss of nitrogen as seen in the lab.