ScienceDaily (Mar. 25, 2009) — In Houston, Texas, understanding atmospheric processes that control pollution formation is complicated by both typical urban emissions and large industrial emissions sources—many of the nation's petrochemical facilities are located in southeastern Texas, and these sources release ground-level ozone precursors including nitrogen oxides and highly reactive organic compounds.

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.

During the summer of 2006, nytril chloride mixing ratios of more than 1 part per billion (ppb) were measured in the Houston urban area.

Through photochemical modeling, the authors find that nytril chloride increases the total reactive chlorine mass by 20 to 40 percent in the atmosphere of southeastern Texas. The nytril chloride caused widespread increases in ozone concentrations over Houston of 1 to 2 ppb; vertical dispersion and local atmospheric composition moderated the effect of nytril chloride on ozone mixing ratios.

The authors include: H. Simon: Center for Energy and Environmental Resources, University of Texas at Austin, Austin, Texas, U.S.A.; now at Atmospheric Modeling and Analysis Division, National Exposure Research Laboratory, Environmental Protection Agency, Research Triangle Park, North Carolina, U.S.A.; Y. Kimura, G. McGaughey, and D. T. Allen: Center for Energy and Environmental Resources, University of Texas at Austin, Austin, Texas, U.S.A.; S. S. Brown, J. M. Roberts: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado U.S.A.; H. D. Osthoff: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado U.S.A.; now at Department of Chemistry, University of Calgary, Calgary, Alberta, Canada; D. Byun: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, U.S.A.; now at Air Resources Laboratory, Office of Ocean and Atmospheric Research, NOAA, Silver Spring, Maryland, U.S.A.; D. Lee: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, U.S.A.

Journal reference:

1. Simon et al. Modeling the impact of ClNO₂ on ozone formation in the Houston area. Journal of Geophysical Research, 2009; 114D00F03 DOI: 10.1029/2008JD010732

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