How do you know whether forest fires or factories and diesel generators are responsible for Black Carbon or CO2 in the air or deposited in icefields? An experiment called CARVE (Carbon in Arctic Reservoirs Vulnerability Experiment) led by Chip Miller of the NASA Jet Propulsion Laboratory was conducted in Alaska’s airspace and some results just published explain how the source can be identified. The combustion of woody biomass (or more importantly in Alaska–layers of compacted dead moss and organic soil) liberates primarily carbon deposited since World War II into CO2. That modern post-bomb carbon contains traces of radioactive carbon (Δ14C) in contrast to fossil fuels, deposited in prehistoric times, which have none.
CARVE: Sherpa aircraft flew sensors over fires in Alaska in 2013 to measure atmospheric concentrations of gases.
During the CARVE experiment, Sherpa aircraft flew sensors to measure atmospheric concentrations of CH4, CO2, and CO and parameters that control gas emissions (i.e. soil moisture, freeze/thaw state, surface temperature). They directly flew over some fires (including fires near Fairbanks and Delta) to measure the “fingerprint” concentrations of isotopes released by typical boreal burning. Mouteva et al. (2015) published findings that showed most of the C in the summer skies over Alaska in 2013 was indeed attributable to forest fires and the age of the biomass converted to black carbon averaged about 20 years (range 11-47 yrs). The authors also explore using the carbon isotope “fingerprint” of fires to estimate the average depth of consumption–since Δ14C increases with depth from the surface moss to the mesic horizon. Pooled results of radioactive isotope fractions yielded an average depth of burn of about 8 inches for the 2013 Alaska fires–a result that may vary depending on fuel conditions. Burn severity, expressed as depth of consumption, is a hot topic among agencies and land managers because it drives ecological response to burning as well as vegetation changes which may come with the hypothesized climate-driven increased boreal burning.
Citation: Mouteva, G. O., et al. (2015), Black carbon aerosol dynamics and isotopic composition in Alaska linked with boreal fire emissions and depth of burn in organic soils, Global Biogeochem. Cycles: 29, doi:10.1002/2015GB005247.
National experts will be giving a talk to bring you up to speed on this issue if you’d like to know more about sources of soot in the atmosphere (including wildfire) and whether pollution control efforts are having any effect. Speakers include: In-situ ground sensing: Patricia Quinn (NOAA); Satellite remote sensing: Ralph Kahn (NASA); and Transport modeling: Mark Jacobson (Stanford).
Date: April 18, 2014 Time: 3:00-4:30 EDT (that’s 11:00-12:30 Alaska Daylight time) Register at IARPC Collaboration website.
The Atmosphere Collaboration Team of the Interagency Arctic Research Policy Committee (IARPC) is hosting the second of two webinars on black carbon which are open to the community. The intent of the second webinar is to share information about current science questions and activities related to Arctic black carbon. Experts will be on hand to share information and answer questions in an effort to inform the Atmosphere Collaboration Team of IARPC of possible future interagency activities related to Arctic black carbon.
Black carbon is “the second most important human emission in terms of its climate-forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing.” When BC is deposited on snow and ice, it darkens an otherwise bright surface. The darker surface may enhance the absorption of solar radiation resulting in an acceleration of snow and ice melting. In addition, BC particles suspended in the atmosphere absorb solar radiation and heat the surrounding air. Atmospheric BC can also alter cloud properties leading to changes in cloud amount and precipitation. Black carbon has multiple sources including domestic combustion for heating and cooking, diesel combustion related to transportation, fossil fuel and biofuel combustion for power generation, agricultural burning, and wildfires. Identification of the sources and types of black carbon (both the geographical region of the source and the combustion process) is necessary for effectively mitigating its climate impacts. In addition, measurements of black carbon are required to verify whether implemented mitigation strategies that target BC emissions from certain sources are actually leading to reductions in BC concentrations in the Arctic atmosphere and surface. In 2013, NOAA’s Arctic Report Card added a black carbon assessment to the Atmosphere Section; the primary conclusions of the assessment are that (1) the average equivalent black carbon concentrations in 2012 at locations Alert (Nunavut, Canada), Barrow (Alaska, USA) and Ny-Alesund (Svalbard, Norway) were similar to average EBC concentrations during the last decade and (2) equivalent black carbon has declined by as much as 55% during the 23 year record at Alert and Barrow (Sharma et al. 2013).