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St. Louis scientists say brown carbon from wildfires is more dangerous than they thought

 Wildfires in California are on the rise. Now a new investigation shows how those blazes are affecting the air in the Midwest.
Crysta Henthorne
Wildfire smoke may produce more damaging smoke particles than scientists had thought, according to a study led by Washington University researchers. Scientists say when wildfires emit dark brown carbon and soot into the atmosphere, they warm temperatures and harm respiratory health.

Wildfire smoke may produce more damaging smoke particles than scientists had thought, according to a study led by Washington University scientists.

The research team worked with NASA and the National Oceanic and Atmospheric Administration in 2019 to examine wildfire smoke across California, Idaho, Oregon and Arizona. Scientists analyzed the smoke produced by megafire events and the carbon emitted into the atmosphere and observed more light absorption from dark brown carbon, a previously overlooked particle.

Dark plumes caused by wildfires emit soot into the atmosphere that absorb light and radiation, which can remain in the atmosphere for as long as 10 days, trapping heat. Researchers found that another particle, organic carbon — also known as dark brown carbon — is present in dark plumes that, like soot, can stay in the atmosphere absorbing light and radiation.

Soot, also called black carbon, warms the atmosphere, keeping temperatures stagnant and changing weather patterns. When brown carbon and soot are released, the particles can accelerate climate change and cause respiratory problems, said Rajan Chakrabarty, associate professor of energy, environmental and chemical engineering at Washington University.

“The conventional wisdom is that dark plume contains soot, but what we find is that a dark plume contains soot but it also contains this highly absorbing organic carbon which previously has been overlooked,” said Chakrabarty, who led the research team.

Climate models have long focused on soot’s effect on the atmosphere, but those models need to be updated to include brown carbon, Chakrabarty said.

The report comes as powerful wildfires are causing damage across the country. Fires in Maui have killed more than 100 people and destroyed thousands of buildings while Canadian wildfires destroyed more than 33.4 million acres and produced smoke that spread across much of the U.S.

Smoke from the Canadian fires made its way into the St. Louis region earlier this summer, limiting visibility and worsening air quality. Chakrabarty said that while wildfires aren’t spreading in Missouri, their effects could still impact air quality. When carbon emitted from the smoke remains in the atmosphere, the region’s temperatures could see a change.

“You have like a blanket of light absorbing air pollutants sitting on top of the city, and that just ensures that you do not have that much of a fluctuation between daytime highs and nighttime lows, it’s going to be pretty flat,” Chakrabarty said. “And that's the enhanced warming effect we are talking about. If you have this layer of air pollutants sitting throughout for an extended period of time, then you could have much hotter days.”

Air pollutants like brown and soot are regulated by the federal Clean Air Act. A spokesperson for the Missouri Department of Natural Resources said that while federal and state regulations are designed to control those pollutants, most emission controls target air pollution from man-made sources such as coal and wood burning.

“There's not really much Missouri can do about wildfires in Canada or California, but what they can do is address the additional sources of whatever the pollutant is within its borders,” said Sarah Rubenstein, staff attorney for Great Rivers Environmental Law Center. “I do think though that if the wildfire problem continues, there's going to have to be something else that's going to have to be done about it or else we're going to be in a situation where we're just constantly dealing with smoke and particulate matter that we're breathing every summer.”

But recent wildfires have led some scientists to urge federal leaders toallow states and Native American tribes to consider prescribed burns.

Chakrabarty said researchers already are looking into how much dark brown carbon is released from other sources other than wildfires.

“Now that we know the prevalence of these particles at least in one emission sector which is wildfires, we need to further carry out investigations and quantify the math as well as the impact of these particles from other sectors,” Chakrabarty said. “When you have qualified numbers and potential health impact information, that information that you provide the policymakers and organizations institutions such as EPA to enact some regulatory measures.”

Chad is a general assignment reporter at St. Louis Public Radio.