MEXICO: Now, a new study has found that on everyday basis, sunlight breaks down grime and releases smog-forming compounds. Up until now, grimy urban buildings weren’t included in models that assess how polluted an urban area is, but the new findings suggest their contribution is significant.
This filth covering buildings, sidewalks, statues and other urban structures are chemicals emitted by air pollution from cars, buses and factories.
A phenomenon never studied before, the release of nitrogen oxide compounds that reside in the building-coating grime is something that Dr. James Donaldson of Toronto University in Canada has been concerned about.
After six weeks, the researchers found that grime collectors in sunny spots in Leipzig had 10% more nitrates than their shaded counterparts, suggesting that the sunlight prompted NO2 and HONO pollution from the grime. Among these compounds are nitrogen oxides. Apparently, the urban grime that creeps on buildings reacts when sunlight hits, causing air pollution.
But scientists had long suspected that nitrogen oxides become inactive when they are trapped in grime and settle on a surface. When in the air, these compounds may combine with other air pollutants-known as volatile organic compounds-and light to produce ozone, which is the main component of smog.
Smog – composed of ground-level ozone, sulfur dioxide, nitrogen dioxides and carbon monoxide – is not only rich in greenhouse gases, but also in chemicals that put people at risk of premature death, aggravate asthma and trigger other respiratory and cardiovascular diseases. In previous work, they discovered that nitrate anions disappeared from grime at faster rates than could be explained by wash-off due to rainfall. The collectors contained glass beads providing larger surface area for the grime to deposit on.
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