The grime that accumulates on windows, buildings, roads, and other surfaces in urban areas could be an important source of nitrogen oxide air pollutants, scientists in Canada conclude in a new report. Nitrogen oxides, emitted in the burning of fossil fuels, combine with other air pollutants termed volatile organic compounds to form smog.
In the report, D. J. Donaldson and colleagues point out that air pollution researchers have been focusing on urban surface films, often termed "window grime," as a potential contributor to air pollution. The films contain nitrogen compounds, which disappear at rates that can’t be explained by obvious losses due to rain washout. In addition, traditional models of urban air pollution suggest that there must be an important but unrecognized source for one nitrogen compound involved in smog formation.
Their study presents experimental evidence suggesting that windows and other surfaces in urban areas may be sites where "inactive" nitrogen oxides may be transformed into "active" forms and be released to the atmosphere. This transformation may occur in a process triggered by sunlight shining on film-covered surfaces, the report notes.
Article: "Photochemical Loss of Nitric Acid on Organic Films: A Possible Recycling Mechanism for NOx", American Chemical Society, Environmental Science & Technology, Scheduled for publication June 15, 2007.
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