Research Highlight: A Lingering Hazard

Annie Reisewitz

While wildfires were threatening much of San Diego County and its residents last month, several researchers from Scripps Institution of Oceanography at UC San Diego were analyzing the soot in local air to better understand the implications of urban fires as well as their implications on climate.
Health and air quality are major concerns during wildfires, yet very little data has been collected on health effects in metropolitan areas, according to Scripps Professor of Atmospheric Chemistry Kim Prather.  Urban fires that destroy homes, businesses, and vehicles emit particulates in the air from a variety of natural and synthetic sources, not just from wood and grass as in a forest fire. Some of those particles are known carcinogens and too small to be stopped by the paper masks worn by many San Diego residents during the fires.
“By examining data collected on the amount of particulates in the air and comparing it to hospital admissions for respiratory and cardiovascular problems during the fires, we will be able to learn a great deal about the public health threat of urban fires,” said Prather.
During and after the fires, Prather’s lab collected data and provided information directly to the public in real-time, streaming on its website.  A specialized instrument Prather helped invent, known as the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS), collects real-time measurements on the number, size, and chemical composition of particulates that pass through the spectrometer’s intake. The researchers were immediately able to determine the types and sources of particles that exceeded California and federal standards for air quality.

These particles in the atmosphere can also have profound implications on climate, Prather said. As soot and other aerosols rose, they traveled over the ocean and into the atmosphere where Scripps scientists had the chance to study how fires impact the climate.

After the initial week of fires, the sooty air from the recent wildfires made its way 1,600 kilometers (1,000 miles) off the coast of California, but San Diego residents weren’t breathing easier. Particle concentrations had decreased to half their peak levels following the initial days of burning but were still unsafe.  As particles age in the atmosphere, they can become more toxic, according to Prather.

“We will use the measurements we collected in our lab to better understand how they affect our local climate over the weeks following the fire,” said Prather.

Similar research conducted in India by Scripps climate researcher V. Ramanathan has shown that high levels of pollution over long periods of time can cause drought conditions because the particles can't grow large enough to combine with atmospheric moisture to become raindrops, noted Prather.

Prather was one of several Scripps researchers who observed the fires’ effects from the ground, at sea, and from space. Jens Mühle, a colleague of Prather’s at Scripps, said that data from the wildfires that swept through Southern California in 2003 suggest that this year’s fires will significantly contribute to the state’s yearly greenhouse gas emissions. Mühle and Prather recently published a study on emissions from the 2003 wildfires which found that emissions of carbon dioxide and methane, both major greenhouse gases, represented between 3 and 7 percent of the entire state’s emissions that year.

The 2007 wildfires, estimated at about two-thirds of the area burned in 2003, will likely produce higher than average emissions again this year, said Mühle.

In addition, Scripps graduate students Chris Dupont and Drew Lucas collected surface water samples and hydrographic data off the San Diego coast from the Scripps research vessel New Horizon in the days after the fires.  The samples will be analyzed in biochemist Kathy Barbeau's laboratory in order to characterize the chemical content of particles the blazes deposited into the coastal ocean.

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