Publication Date:
2015-10-09
Description:
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 (PM 2.5 ) and measured its radiocarbon (Δ 14 C) content with accelerator mass spectrometry (AMS). 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 Δ 14 C of BC from boreal fires was 131 ± 52‰ in year 2013 when the Δ 14 C of atmospheric CO 2 was 23 ± 3‰, corresponding to a mean fuel age of 20 years. Fire-emitted OC had a similar Δ 14 C (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 PM 2.5 . Fire-emitted aerosol had an elevated carbon to nitrogen (C/N) ratio (29 ± 2) and δ 15 N (16 ± 4‰). Aerosol Δ 14 C and δ 13 C 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 PM 2.5 composition constrain the endmember 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.
Print ISSN:
0886-6236
Electronic ISSN:
1944-9224
Topics:
Biology
,
Chemistry and Pharmacology
,
Geography
,
Geosciences
,
Physics
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