Scientists studying the angry smoke boiling from the fiercest of wildfires have made a discovery that might prove important when it comes to understanding a changing climate.
Researchers at Reno's Desert Research Institute have found a previously unrecognized type of soot particle, different than the soot emitted from sources such as vehicles and cook stoves, that might play an important role in atmospheric warming trends around the globe.
"These larger particles tend to warm the atmosphere more than conventional soot," said DRI graduate student Nicholas Beres, an author of a study recently published in Nature Scientific Reports. "We believe they probably could play quite a big role."
Scientists have long labored to quantitatively assess the effect of wildfire soot particles on climate change, with wildfires believed to be responsible for some 34 percent of the global soot mass emitted into the atmosphere. These efforts come as fires grow larger and more frequent and fire seasons are lasting longer, with studies suggesting those trends will continue in coming decades.
It hasn't been an easy task. After all, wildfires are unpredictable and sampling smoke from fires burning at peak intensity is difficult to say the least. Most studies of wildfire smoke involve samples taken during a fire's later stages as it is dying down and smoldering.
On assignment with scientists in the Maldive Islands in 2012, Beres was in the right place at the right time — with the proper equipment — to sample thick smoke billowing from a fire raging in western India. Analysis by electron microscope of the smoke from torching teak and bamboo revealed the presence of what researchers dubbed "superaggregates" — soot particles more compact and on average 10 times longer than normal ones.
Further research identified those same particles present in smoke samples taken during wildfires burning in Northern California in 2010, in New Mexico in 2011 and outside Mexico City in 2006. Superaggregates, Beres said, are formed at the height of a fire when it's burning its hottest.
"It has to be really hot. It has to be really intense," Beres said. "The particles are getting sucked back in and glom on with other particles to form these superaggregates."
Researchers have noticed the things before but essentially wrote off their difference from regular soot particles. They deserve more attention when it comes to climate modeling, DRI researchers said.
"Our observations suggest that we cannot simply assume a universal form of soot to be emitted from all combustion sources," said Rajan Chakrabarty, the DRI researcher who was lead author of the study.
"Large-scale combustion sources, such as wildfires, emit a different form of soot than say, a small-scale controlled combustion source such as vehicles," Chakrabarty said.
So why is this different type of soot potentially important when it comes to climate change? Calculations suggest superaggregates could have a 90 percent greater warming effect on the atmosphere than do regular soot particles.
"We found that superaggregates contribute up to 90 percent more warming than spherical sub-micrometer soot particles, which current climate models use," Chakrabarty said. "These preliminary findings warrant further research to quantify the significant impact these particles may have on climate, human health and air pollution around the world."
Kelly Redmond of Reno's Western Regional Climate Center, not involved in the study, agreed the issue deserves more attention. While much is known about how greenhouse gases such as carbon dioxide are driving a changing climate, much less is known about the impacts of aerosols such as soot.
"All the gases are the same, every C02 molecule is the same," Redmond said. "Soot, sand, dust, air pollution, all those sort of things that float around in the atmosphere are different. The effect of aerosols on climate has become more and more of an issue. If we don't know what aerosols do, we have an incomplete picture."