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Sea Salt May Contribute to Ground-level Ozone Formation
Posted: July 22, 2009
What do sea salt, ground-level ozone, and an energetic EPA scientist named Dr. Heather Simon have in common? They have come together to provided new information about how sea salt mixing in the atmosphere impacts the air we breathe.
Ground-level ozone is created from natural and man-made emissions and is therefore a challenging pollutant to control. That is one reason why EPA invests in research to understand how chemicals in the atmosphere react with sunlight, mix, and are dispersed in the air.
Sea salt in the atmosphere mixes with oxides of nitrogen in polluted air to form a new chemical: nitryl chloride, says Simon. The addition of nitryl chloride in the atmosphere forms reactive chlorine, which has an impact on ozone formation.
“This study was exciting because we were the first to include nitryl chloride chemistry in a photochemical dispersion model and to see its effect on Houston, Texas, an area which has struggled to bring down its ozone levels,” Simon explained. “Having the actual measurements from a recent field study motivated us because they provided the first direct evidence that this chemistry is significant in coastal environments such as Houston.”
Simon, a researcher in the Atmospheric Modeling and Analysis Division of the EPA’s National Exposure Research Laboratory, is part of a team that investigated the impacts of chemical reactions involving sea salt on air quality — specifically ozone formation. A paper on these findings, authored by Simon and colleagues, titled, “Modeling the Impact of ClNO2 on Ozone Formation in the Houston Area,” was published in the Journal of Geophysical Research in February 2009 and recently was highlighted on the Web site of the American Geophysical Union.
This paper is among the first comprehensive modeling studies to take nitryl chloride measurements into account in the evaluation of urban ozone formation. The team’s findings indicate that future ground-level ozone levels could increase slightly because of chemical reactions involving sea salt and oxides of nitrogen produced from pollution.
The photochemical modeling conducted for this research found positive news as well: Reductions in nitrogen oxide emissions gained through reducing emissions from combustion and industrial processes may be more effective at decreasing ozone levels than previously thought. Modeling studies will need to be conducted in a variety of coastal urban areas to examine this phenomenon.
This new knowledge provides valuable data to the atmospheric sciences and modeling communities. For EPA, including nitryl chloride chemistry in the atmospheric mix provides additional data for use in advanced modeling tools that can be used in developing mitigation strategies to reduce air pollution. The findings also provide air quality managers at state and local levels with awareness about how sea salt reacts with nitrogen oxide to affect the quality of the air we breathe.