Scientists Link Urban Air Pollution to Distant Forest Fires

MODIS (Terra) data show a smoke cloud over Houston
MODIS (Terra) data shows a smoke cloud over Houston on 19 July 2004 when ozone levels in Houston were notably higher from the surface to 4 km altitude. Image is courtesy of MODIS Rapid Response Project at NASA GSFC, and the Journal of Geophysical Research.

In an example of how far-reaching the effects of a natural hazard can be, a team of 15 scientists has documented how forest fires burning on the border between Alaska and Canada caused serious air pollution in Houston, Texas, more than 5,000 kilometers away. Their findings were published in the September 2006 issue of the Journal of Geophysical Research.

During the summer of 2004, forest fires in eastern Alaska burned a total of 2.7 million hectares, 10 times the area normally affected by wildfires in the state, setting an annual record. An additional 3.1 million hectares went up in flames across Canada over the same period, half of them in the western Yukon Territory adjacent to Alaska.

The scientists report that smoke from fires on July 12–14 drifted across Canada, down the Mississippi River valley, and through Dallas, eventually settling in Houston nearly a week later (July 19–20). For the several days that the smoke cloud lingered over Houston, ground-level ozone levels (measured at 0–5 kilometers above the Earth’s surface) increased 50 to 100 percent, resulting in the highest eight-hour maximum ozone levels ever recorded for a July day in Houston between 2001 and 2005.

Houston is routinely affected by above-average ozone levels. Home to the fourth largest population in the United States, as well as numerous petrochemical production plants, the city often leads the nation in the number of days its air violates U.S. Environmental Protection Agency ozone standards. The American Lung Association ranked Houston the sixth most ozone-polluted city in the United States in 2006, behind five California cities, including Bakersfield and Los Angeles.

Ozone pollution, also known as smog, forms when pollutants from factories, electric utilities, vehicle exhaust, gas vapors, and chemical solvents interact with heat and sunlight. Besides clouding the air, smog can contribute to serious health problems— triggering breathing problems, aggravating asthma and emphysema, and potentially causing permanent lung damage in children. The World Health Organization estimates that 800,000 people die each year from smog and other forms of air pollution.


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