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.
Reporting in the Journal of Geophysical Research-Atmospheres, Simon et al. determine that the pollution profile in Houston is further complicated by its proximity to the ocean. Nitryl chloride, a compound created by the reaction of sea salt with an oxide of nitrogen produced in urban atmospheres, can photodissociate into nitrogen dioxide and chlorine atoms. The former is a pollutant, and the latter has been shown to increase ground-level ozone formation.
Chlorine salts are naturally present in coastal air in sea salt aerosols, which are swept from the ocean into the air by the wind. Chlorine gas also is used to treat water in swimming pools, cooling towers and municipal water supplies. Chlorine atoms react rapidly with hydrocarbons and nitrogen oxides from automobile and power plant emissions, contributing to the complex chain of reactions that leads to ozone formation. The primary cause of urban ozone is the reaction of hydroxyl radical (OH) with hydrocarbons and nitrogen oxides. OH is a highly reactive molecule made of oxygen and hydrogen that forms photochemically in air.
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