NCAR Analysis Shows Widespread Pollution From 2004 Wildfires

The NCAR study, which indicates the extent to which wildfires contribute to atmospheric pollution, was published this month in Geophysical Research Letters. The researchers used a novel combination of observing instruments, computer models, and numerical techniques that allowed them to distinguish between carbon monoxide coming from the wildfires and from other sources.

The team concluded that the Alaskan and Canadian wildfires emitted about 30 teragrams of carbon monoxide from June through August of last year. Because of the wildfires, ground-level concentrations of ozone increased by 25% or more in parts of the northern continental United States and by 10% as far away as Europe.

"It is important to see how the influence of these fires can reach large parts of the atmosphere, perhaps even over the entire Northern Hemisphere," says NCAR scientist Gabriele Pfister, the study's lead author. "This has significant implications as societies take steps to improve air quality."

Carbon monoxide, a toxic gas that can affect human health even at low levels, is emitted by wildfires as well as by motor vehicles, industrial facilities, and other sources that do not completely burn carbon-containing fuels. Ground-level ozone, which affects human health in addition to damaging plants and influencing climate, is formed from reactions involving atmospheric pollutants, including carbon monoxide, in the presence of sunlight. Both pollutants are monitored by the Environmental Protection Agency. However, scientists have been unable to precisely determine regional emissions of carbon monoxide or the extent to which human and natural activities contribute to atmospheric concentrations of the gas.

Wildfires in Alaska and western Canada were particularly intense in the summer of 2004, largely because of unusually warm and dry weather. To quantify carbon monoxide emissions from the fires, the research team used a remote sensing instrument known as MOPITT (Measurements of Pollution in the Troposphere) that is operated by NCAR and the University of Toronto and flown on NASA's Terra satellite. The scientists simulated the transport of the pollutants emitted by the fires and the resulting production of ozone with an NCAR computer model called MOZART (Model for Ozone and Related Chemical Tracers).

The team confirmed its results by using numerical techniques to compare simulated concentrations of carbon monoxide in the atmosphere with measurements taken by MOPITT. The researchers were able to get further confirmation by analyzing data from aircraft-mounted instruments that were taking part in a field project over North America and Europe.

Pfister says the team is continuing to look at data taken last year at observing stations as far away as the Azores in order to track the movement of carbon monoxide and ozone from the wildfires. As a follow-up, she and other scientists plan to use a similar combination of observations, modeling, and numerical techniques to look at both natural and human-related emissions of carbon monoxide in South America.

The research was funded by a NASA grant in partnership with the National Science Foundation, which is the primary sponsor of NCAR.