IARPC External Collaborations Webinar: Black Carbon II
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).
Several issues are currently challenging the Arctic black carbon research community:
- In-situ measurements are the most reliable measure of black carbon; however, the most prevalent techniques which involve filter samplers only make proxy black carbon measurements.
- Retrievals of aerosols optical depth (AOD) over snow and ice-covered surfaces with passive remote sensing from vis-NIR imagers from space are problematic. Some success over incomplete snow-covered surfaces has been achieved, e.g., with MISR. TOMS, OMI, and probably now OMPS UV passive imaging has some qualitative sensitivity (the Aerosol Index), though with limited sensitivity to near-surface aerosol, and CALIPSO lidar is by far the most sensitive, but with limited coverage.
- Standardized ground-based networks such as AeroNET, MPLNet, and BSRN have sparse and sporadic Arctic coverage, and are uncoordinated with the necessary black carbon-in-snow measurements, and some long-standing surface stations have actually been decommissioned in the past few years.
- A promising approach to assessing high-latitude aerosol effects is to constrain aerosol transport models with satellite observations taken at lower latitudes, near the aerosol sources (mainly Boreal fires and pollution sites) where and when the surface is not snow-covered.
- In-situ ground sensing: Patricia Quinn (NOAA)
- Satellite remote sensing: Ralph Kahn (NASA)
- Transport modeling: Mark Jacobson (Stanford)
For more information on how to join the webinar, please visit the website link above.