February 10, 2003

Current air-quality models used for predicting air pollution may be underestimating ozone levels in Southern California by as much as 10% of the national one-hour ozone standard, a UC Irvine study has found.

Donald Dabdub, UCI professor of mechanical and aerospace engineering, and post-doctoral researcher Eladio Knipping reached this conclusion after making adjustments to a computer model that calculates pollution levels in the South Coast Air Basin of California.

In adjusting the model, the researchers added the impact of sea-salt particles in the coastal air. These salts release small amounts of chlorine, which mixes with smog and morning sunlight to create small amounts of ozone. Currently, sea salt-derived chlorine information is not included in any official regulatory models.

Dabdub and Knipping determined that predicted ozone levels could increase by as much as 12 parts-per-billion (ppb) in coastal regions and afternoon peak levels by 4 ppb. In comparison, Southern California peak ozone levels in 2001 exceeded the one-hour national standard of 120 ppb on 36 days and the one-hour California stadard of 90 ppb on 121 days. Study results appear in the Jan. 15, 2003 issue of Environmental Science & Technology.

"The chemistry of sea-salt particles appears to be important for correctly predicting air pollutant concentrations in coastal urban regions," said Dabdub, who studies the mathematical modeling of air pollution. "Inclusion of sea-salt chlorine chemistry should be considered in order to improve regulatory models in coastal regions."

An earlier UCI study first determined that sunlight, pollutants and ocean spray combine to enhance the urban production of ozone. The study found that sea-salt particles in coastal air undergo a chemical reaction on their surface, which in turn releases chlorine molecules. Sunlight then breaks down these molecules into individual, highly reactive chlorine atoms. When these atoms enter the chemical stew of early-morning smog, they react with fossil-fuel pollutants and contribute to the formation of ozone.

Ozone is a pollutant that is commonly created when combustion emissions and other sources react to sunlight. It is known to irritate the tissues of the eyes, nose and lungs, causing inflammation and breathing difficulties.

The National Science Foundation and California Air Resources Board supported the work.

This text derived from http://www.today.uci.edu/news/release_detail.asp?key=973

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