Air measurements taken nearly nonstop in the Irvine area over a two-month period showed that daytime chlorine gas levels typically measured five parts per trillion or less, but occasionally reached as high as 15 parts per trillion. Observation of daytime chlorine is surprising because chlorine molecules break apart just minutes after entering the atmosphere and being exposed to sunlight.

With these measurements, scientists estimate that chlorine photochemistry creates five to eight parts per billion of the maximum daily ozone level, which in California typically ranges between 40 and 80 parts per billion.

"Chlorine chemistry can have a direct impact on surface ozone even at parts per trillion levels," said Eric Saltzman, professor of Earth system science in the School of Physical Sciences at UCI. "Because of the strong link between ozone and human health, we need to fully understand the role chlorine may play in ozone chemistry in coastal urban environments."

Saltzman and Brandon Finley, a graduate student researcher in the Department of Earth System Science, published their findings in the current issue of Geophysical Research Letters.

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
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Contact: Christine Byrd
cbyrd@uci.edu
949-824-9055
University of California - Irvine
13-Jun-2006