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Fiery Origin Of Climate-Warming Aerosols

Study finds that fires producing more black carbon also yield so-called brown carbon, helping clarify inputs into climate models

by Jyllian Kemsley
August 12, 2014 | A version of this story appeared in Volume 92, Issue 32

Credit: Daniel Tkacik/Carnegie Mellon U
A cut-grass fire burns at the Missoula Fire Sciences Laboratory.
Photo of a cut-grass fire at the Missoula Fire Sciences Laboratory.
Credit: Daniel Tkacik/Carnegie Mellon U
A cut-grass fire burns at the Missoula Fire Sciences Laboratory.

Wildfires have burned nearly 2 million acres in the U.S. so far this year, underscoring the importance of a study that provides better insight into the climate effects of organic aerosol particles emitted into the atmosphere from burning forests, grasslands, and farmland. Climate models have historically divided airborne particulate matter produced by biomass burning into two categories: light-absorbing black carbon (soot) that warms the climate and light-scattering organic aerosols that cool the climate. But researchers are finding that organic aerosols known as brown carbon can also be light-absorbing. In the new study, a team led by Allen L. Robinson and Neil M. Donahue of Carnegie Mellon University analyzed particles released from fire experiments conducted at the Missoula Fire Sciences Laboratory in Montana (Nat. Geosci. 2014, DOI: 10.1038/ngeo2220). They found that oxygen­-deprived, fuel-rich fires that tend to produce high amounts of black carbon also produce brown carbon, and brown carbon aerosols are associated with extremely low volatile organic compounds possibly similar to humic substances. The results could help explain a mismatch between the amount of aerosol-driven global warming predicted by climate models compared with what’s actually being observed.


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