Breathe Easy


If it’s 5  a.m. in Mexico City, then the smog the city is breathing is by and large incinerated municipal waste in particulate form.

But by 3 p.m., wind patterns have changed. Mexico City residents are more likely to be inhaling aerosols ejected with the smoke of fireslocated south of the city.[MSOffice1]

So go the conclusions of a recent analysis of air pollution patterrns in the world’s eighth largest city, and one of its smoggiest, by researchers at Scripps Institution of Oceanography at UC San Diego and six other institutions. Using a mass spectrometer that can characterize the chemical composition of smog particles in near-real time, the researchers hope to play a role in improving public health as well as understand how aerosols affect climate.

“Our instrument brings in a new level of precision by allowing us to identify high levels of specific pollutants that occur in transient peaks,” said Scripps atmospheric chemistry professor Kim Prather, who also holds an appointment at UCSD’s Department of Chemistry and Biochemistry.  “A harmful type that is present in high amounts for just a few hours might be overlooked in a sample collected over the course of an entire day and night. But if you live nearby, you still breathe air with concentrated pollutants.”

The findings, which the scientists recently reported in the journal Environmental Science and Technology, add to an emerging discussion of the role and importance of aerosols in influencing climate. In August, that new interest was underscored by the opening of the Aerosol Chemistry and Climate Institute, a collaboration of Scripps and the Pacific Northwest National Laboratory that Prather co-directs.

One of the institute’s first missions will be to understand the role aerosols play in making weather cycles even more complex. Aerosols like dust, smoke and even microorganisms are the scaffolding that enable cloud formation. When aerosols from human activities — whether a diesel-powered car ejecting exhaust or a street vendor’s cart emitting soot from its charcoal grill — are added to the mix, the results can be subtle but profound. Prather’s colleagues at Scripps like atmospheric and climate sciences professor V. Ramanathan have documented how human-produced aerosols can alter rainfall patterns and affect agricultural output.

Instruments like the aerosol time-of-flight mass spectrometer (ATOFMS) developed by Prather have dramatically improved scientists’ ability to track aerosols as they drift through the atmosphere. The institute plans to establish an aerosol observatory at the end of Scripps Pier that will characterize the mix of pollutants that come to San Diego from Mexico, Asia, and local sources.

“Changes in aerosols could affect Earth’s temperature on a much shorter time scale than greenhouse gases,” said Prather. “Sorting out the role of aerosols in climate could buy us some time as we grapple with the challenge of controlling levels of the greenhouse gases.”

—Robert Monroe and Susan Brown


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