Droughts and fires affecting Western U.S. air quality

New study tracks increase in summertime haze in Colorado wilderness

Summit County firefighters extinguish a small wildfire between Keystone and Montezuma late March, 2012.
Summit County, Colorado, firefighters extinguish a small wildfire between Keystone and Montezuma late March, 2012. A new University of Utah study suggests that more drought and wildfires will worsen air pollution in the high country of the West, even spreading to pristine wilderness areas. @bberwyn photo.

Staff Report

Longer and hotter droughts and wildfires are polluting the once clear blue skies of the high country in the West, according to new research from the University of Utah.

The study, published this week in the journal Environmental Research Letters, found a link between the severity of drought in the Intermountain West and summertime air quality. Climate projections suggest that drought and wildfire risk will continue to increase in coming decades.

“If you take that into the future, we’re going to see significant hazing of the West,” said University of Utah atmospheric scientist Gannet Hallar.

Haze in the air is caused by small airborne particles–typically dust, soot, ash or smoke. Aerosols are particles so small that they are suspended in air and don’t settle out. Fog and steam can also be considered aerosols.

The buildup of haze will also affect climate on a regional scale, according to the scientists. Mineral grain dust particles can reflect solar energy, thereby cooling the climate. But aerosols derived from organic carbon, like soot and smoke,  absorb energy and trap more heat. aerosol particles can also trigger cloud formation, which exerts its own influence over global temperature and climate.

Hallar conducts research at the Desert Research Institute’s Storm Peak Laboratory, near Steamboat Springs, Colorado, at an elevation of 10,525 feet above sea level. The labmeasures aerosol optical depth, the amount of aerosols between the sensor and the sun.

Researchers noticed that decades of aerosol optical depth records consistently showed increases in the summer. A previous global study of aerosols showed a widespread decrease in aerosol concentrations across the United States except for a summertime peak at a site in the western U.S. So the team of hydrologists and atmospheric scientists looked at climate and drought records for the West to see if they could find a connection to the summer mountain haze.

“It’s the fires. It’s a strong evidence that the drought is probably allowing for more wildfires and the fires are most likely allowing for more aerosols,” Hallar said.

The research showed a correlation between drought and high-elevation aerosols. The observational data can be used to check climate models’ simulated effects of fires on aerosol emissions. The models use assumptions to estimate how much aerosol pollution results from an area of forest burned, which can lead to uncertainties in the conclusions.

“We’re putting a moment of real data in there,” she said, adding that the observational data isn’t far off from what the models predict. “That has me concerned because climate models are predicting in the future a significant increase in organic aerosol loading.”

Even more concerning is that the data came from wilderness areas, preserved for their untouched natural beauty, not to mention specific air quality standards. But a wilderness area’s borders can’t keep the haze out. Hallar hopes that her results highlight the importance of managing the relationship between drought, fire and haze in the West. “We need to think about fires in the realm of air quality,” she says.

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