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Soot From Wildfires May Have More Climate Impacts Than Carbon Dioxide

By Elizabeth Harball, E&E reporter
July 14, 2014; 8:00 AM

Scientists have learned something new about the nasty, dark smoke that rises from wildfires that might have important implications on the climate.

As the U.S. wildfire season is well underway, researchers have detected a new, bigger kind of soot particle emitted by fires that, when released into the atmosphere, has a 90 percent greater warming effect than the particles assumed in current climate models.

These particles are essentially different from those emitted by sources like camp stoves or cars.

The authors of the paper, published this month in Scientific Reports, were not ready to say that the finding proves that wildfires are making climate change worse than previously thought. But they did confirm that the discovery may require an adjustment to today's climate models.

"These superaggregates -- these larger particles [from wildfires] -- may be more abundant in atmosphere than what's previously found in literature," said study co-author Nicholas Beres of the Desert Research Institute in Reno, Nevada.

Army Chief Warrant Officer Chris Aylstock, Capt. Colton Brauer and Sgt. Chris Boni battle the wildfire over Yosemite National Park, Calif., Aug. 22, 2013. The California National Guard UH-60 Black Hawks and HH-60 Pave Hawks are in full force supporting the U.S. Forest Service and California firefighters. Aylstock, Brauer and Boni are assigned to 1st Battalion, 140th Aviation Regiment. U.S. Air Force photo by Master Sgt. Julie Avey. (Credit: Flickr/U.S Army)

"What this research tries to show is that you have to be very particular in choosing the right model of particles in the climate models, especially from wildfires, because they can have an enhanced warming effect," added lead author Rajan Chakrabarty, also of the Desert Research Institute.

Chakrabarty noted that annually, wildfires account for about 34 percent of soot mass that ends up in the atmosphere. Additionally, the recently released National Climate Assessment stated that climate-linked hotter, drier conditions and insect outbreaks in the southwestern United States have already caused wildfires there to happen more often.

According to Chakrabarty, the reason it has taken so long to learn about the larger particles is that it's extremely difficult to take soot samples from active wildfires. Most analysis up until now has been collected from the white smoke emitted from smoldering fires, long after the most intense flames have left the area.

'Superaggregates' identified

But in 2012, Beres was able to collect soot particles as they drifted from the Nagarhole National Forest fire in Karnataka, India, to a climate observatory where he was working in the Maldives.

The research team looked at the material using an electron microscope and discovered larger, fluffier particles that they had never seen before. They found the same kind of particle was also found in samples taken from wildfires that burned in 2010 in California, in 2006 in Mexico and in 2011 in New Mexico.

These soot particle "superaggregates" are created when a fire is in what the researchers call the "flaming phase," when it is hotter and more intense. In this phase, the flames whirl and form eddies like a river, trapping soot particles longer.

"Think about it like you are letting more people into a room which does not have an exit, so you are going to get crowding," Chakrabarty said. "That is what's happening, really, inside these eddies: You have all these soot particles accumulating ... they are coming together and forming these large aggregates."

The researchers also found that these particles can remain in the atmosphere for days because of their low density.

Kostas Tsigaridis, an associate research scientist at Columbia University and NASA's Goddard Institute for Space Studies, said climate scientists are already aware that their models don't do a good enough job representing soot particles.

"It's a weakness, and we want to improve in the future," said Tsigaridis, who was not involved in the research.

Tsigaridis said it was "a very interesting study" with "very interesting science," but he said it is still unclear if its findings have global implications -- wildfires in different parts of the world under different weather conditions may not produce as many of these particles, he said.

However, Tsigaridis allowed that the newly discovered particles "may have really important implications, at least locally."

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.

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