Black carbon aerosol dynamics and isotopic composition in Alaska linked with boreal fire emissions and depth of burn in organic soils
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2015-11
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Journal Article
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yes
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Abstract
Black carbon (BC) aerosol emitted by boreal fires has the potential to accelerate losses of snow and ice in many areas of the Arctic, yet the importance of this source relative to fossil fuel BC emissions from lower latitudes remains uncertain. Here we present measurements of the isotopic composition of BC and organic carbon (OC) aerosols collected at two locations in interior Alaska during the summer of 2013, as part of NASA's Carbon in Arctic Reservoirs Vulnerability Experiment. We isolated BC from fine air particulate matter (PM₂.₅) and measured its radiocarbon (Δ¹⁴C) content with accelerator mass spectrometry. We show that fires were the dominant contributor to variability in carbonaceous aerosol mass in interior Alaska during the summer by comparing our measurements with satellite data, measurements from an aerosol network and predicted concentrations from a fire inventory coupled to an atmospheric transport model. The Δ14C of BC from boreal fires was 131 ± 52‰ in the year 2013 when the Δ¹⁴C of atmospheric CO₂ was 23 ± 3‰, corresponding to a mean fuel age of 20 years. Fire-emitted OC had a similar Δ¹⁴C (99 ± 21‰) as BC, but during background (low fire) periods OC (45 to 51‰) was more positive than BC (−354 to −57‰). We also analyzed the carbon and nitrogen elemental and stable isotopic composition of the PM₂.₅. Fire-emitted aerosol had an elevated carbon to nitrogen (C/N) ratio (29 ± 2) and δ¹⁵N (16 ± 4‰). Aerosol Δ¹⁴C and δ¹³C measurements were consistent with a mean depth of burning in organic soil horizons of 20 cm (and a range of 8 to 47 cm). Our measurements of fire-emitted BC and PM₂.₅ composition constrain the end-member of boreal forest fire contributions to aerosol deposition in the Arctic and may ultimately reduce uncertainties related to the impact of a changing boreal fire regime on the climate system.
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published
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Journal / series
Volume
29 (11)
Pages / Article No.
1977 - 2000
Publisher
American Geophysical Union
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Subject
biomass burning; burn severity; fuel consumption; elemental analysis; climate-carbon feedback; boreal forest ecosystem