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David Bradley ISSUE #65
May 2007
Windows Cause Pollution

This is not another terrible advertisement for an alternative computer operating system to the eponymous installation mentioned in the title, but an environmental analysis that reveals how dirty windows are a major contributor to urban pollution.

James Donaldson

According to James Donaldson and colleagues, Susannah R. Handley and Daniel Clifford, of the University of Toronto, the grime that accumulates on windows, buildings, roads, and other surfaces in urban areas could be an important source of nitrogen oxide air pollutants. The team reports details of their work in a forthcoming issue of the ACS journal Environmental Science & Technology. Nitrogen oxides are produced when fossil fuels are burned and can combine with other air pollutants, termed volatile organic compounds, to form smog.

Could dirty windows and sunlight contribute to smog? (Photo by David Bradley)

Until now, air pollution researchers have not focused on urban surface films, often termed "window grime" as a serious contributor to air pollution. However, these films contain nitrogen compounds, which disappear at rates that cannot be explained by obvious losses due to their being washed off by rain. However, calculations carried out on urban air pollution do not balance properly, they lack a source of nitrogen compounds involved in the formation of smog. Donaldson and his colleagues suggest that window grime is the missing link. The researchers present experimental evidence that windows and other surfaces carry "inactive" nitrogen oxides that can be converted chemically into "active" forms. These active forms can be carried into the atmosphere where they can react photochemically in strong sunlight with volatile organic pollutants to form smog.

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Environ Sci Tech, 2007, in press; http://dx.doi.org/10.1021/es062044z