Dominance of brown carbon in aerosol emissions from burning of boreal peatlands

Abstract

The surface air warming over the Arctic has been almost twice as much as the global average in recent decades. In this region, unprecedented amount of smoldering peat fires have been identified as a major emission source of climate-warming agents. While much is known about greenhouse gas emissions from these fires, there is a knowl-5 edge gap on the nature of particulate emissions and their potential role in atmospheric warming. Here, we report the microphysical properties of aerosols emitted from controlled laboratory combustion of Alaskan and Siberian peatland samples. The emitted aerosols are brown carbon with negligible amount of black carbon content. Their mass absorption efficiencies lie in the range of 0.2-0.8 m 2 g −1 at 405 nm and drop sharply to 10 0.03-0.07 m 2 g −1 at 532 nm, characterized by a mean Ångström exponent of ≈ 9. Their top-of-atmosphere direct radiative forcing over bright surfaces is positive (warming), and their presence in the troposphere may influence photolysis driven chemistry.