Siberian forest fires partly to blame for Seattle area violating EPA ozone limit

Smoke from giant Siberian forest fires pushed one measure of Seattle’s air quality past federal environmental limits on at least one day in 2003, new research shows.

And the rapidly changing climate in northern latitudes makes it likely such fires will have increasingly serious ramifications for air quality all along the West Coast of North America, said Dan Jaffe, an environmental scientist at the University of Washington, Bothell.

“In the past, we haven’t considered that long-range transport can bring in pollution levels that are significant,” Jaffe said. “What we’re finding is that these events can bring in significant levels of pollution, even to urban areas where the levels already are relatively high.”

In the spring and summer of 2003, Siberian forest fires consumed 46.7 million acres, or nearly 73,000 square miles – an area slightly larger than the state of Washington. That was more than twice the annual average from 1996 until 2003. The fires burned most intensely during May and June, and the smoke plume was tracked by satellites and detected during a research flight off the Washington coast on June 2.

Between May 27 and June 9, air quality monitors in British Columbia and Washington detected levels of ozone that were higher than average for that period. Previous daily data had been gathered from May through September in 1996 through 2003. Ozone readings during that time varied according to temperature, but generally ranged from a low of a few parts per billion by volume to around 80 parts per billion. Between June 1 and June 6, the monitor sites recorded ozone nine to 17 parts per billion by volume higher than normal, and the surface monitoring suggested a continual influence from the Siberian fires, as did the June 2 research flight.

On June 6, the ozone-monitoring site at Enumclaw, Wash., about 30 miles southeast of Seattle, registered an eight-hour average of 96 parts per billion by volume. The U.S. Environmental Protection Agency limit is 80 parts per billion for an eight-hour period.

In the upper atmosphere, ozone protects the Earth from harmful solar ultraviolet rays. In the lower atmosphere and at the surface it is a pollutant – found, for instance, in smoke and automobile exhaust – that can cause various health problems, particularly respiratory difficulties.

Ozone levels tend to rise with temperature, but the level recorded on June 6 exceeded what was expected for the temperature that day, Jaffe said. The high temperature that day at Seattle-Tacoma International Airport, about 90 degrees, had been recorded 12 times from 1996 through 2002, with an average eight-hour ozone level of about 79 parts per billion on those days. The 96 parts per billion on June 6 was substantially higher, and virtually all of the excess could be attributed to the Siberian fires.

“Would we have violated the EPA standard without the Siberian fires? It would have been really close. I don’t think we would have,” Jaffe said.

He noted that despite the Siberian smoke, the vast majority of ozone registered in Enumclaw on June 6, 2003, came from local sources.

Jaffe is the lead author of a paper detailing the work that has been accepted for publication in an upcoming issue of Geophysical Research Letters and will be published online Aug. 20. Co-authors are Isaac Bertschi, also from the UW Bothell campus; Lyatt Jaegle from the UW Seattle campus; Paul Novelli of the National Oceanic and Atmospheric Administration; Jeffrey Reid and Douglas Westphal of the U.S. Naval Research Laboratory; Hiroshi Tanimoto of Japan’s National Institute for Environmental Studies; and Roxanne Vingarzan of Environment Canada. The work was supported by grants from the National Science Foundation, the Office of Naval Research and the National Aeronautics and Space Administration.

Previous research has suggested that as climate warms, northern temperate-zone forests are likely to become drier during the spring and summer, with snow melting earlier in the year and creating an earlier and more prolonged fire season.

The new research, Jaffe said, suggests a link between climate change, temperate-zone forest fires, long-range transportation of pollutants and human health. It has health implications throughout western North America, and shows that western U.S. cities might have a harder time in the future meeting air quality standards, he said.

“Siberia has perhaps warmed more than anywhere else on the planet in the last 50 years,” he said. “If there is increasing burning in Siberia, then we will see higher levels of ozone.”