5 February 2009
A study by researchers in the ESRL Chemical Sciences Divison and Global Monitoring Divison published on 30 January in Geophysical Research Letters, has been named as one of the "Editors' Highlights" for that issue. Lead author Carsten Warneke, a CIRES scientist at CSD, and coauthors showed that the 2008 springtime "Arctic haze" over northern Alaska and the Arctic region had unexpectedly high signatures of faraway sources: wildfires and biomass burning activities occurring in Asia. They used data from the April 2008 Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) airborne field experiment, based in Fairbanks, Alaska. Chemical and meteorological instrumentation onboard the NOAA WP-3D aircraft gathered data on more than 50 plumes that were encountered during the six research flights over northern Alaska and the Arctic sea ice. The chemical composition of the plumes and transport modeling led to the authors' finding that most of the plumes were emitted by forest fires in southern Siberia and by agricultural burning in Kazakhstan-southern Russia. An unexpected finding was that these biomass burning plumes were the dominant aerosol and gas-phase features encountered during the April time period of the mission. This was perhaps because the fire season in Siberia started earlier than usual, and therefore transport of the fires' emissions to the Arctic was unusually efficient.
Background: Arctic haze consists of gas-phase and particle pollutants that are likely produced from emissions of pollutants from Europe, Asia, and North America and by episodic plumes released from biomass burning and wildfires. It has been a regular feature at northern latitudes since the 1950s. Slow removal processes for the pollutants leads to the persistence of Arctic haze. The light-absorbing properties of smoke and haze can affect Arctic climate through direct warming of the troposphere, acceleration of snow melting by the absorption of radiation by soot deposited on the surface, and changes in the climate-related properties of clouds. The ARCPAC mission was focused on investigating the chemical, optical, and microphysical characteristics of aerosol particles and gas-phase species in the Arctic springtime to determine the sources (industrial, urban, biomass/biofuel burning, dust, sea salt) of those components.
Significance: The presence of the biomass burning smoke in the surface layer over Arctic sea ice and snow-covered land suggests that light-absorbing aerosols could be efficiently deposited to the snow/ice surface, potentially reducing surface albedo and thereby affecting the radiation balance in the region. Biomass burning is a large source of aerosols in the Arctic, but usually occurs in the late spring or early summer when transport to the Arctic is not as efficient. Earlier starts to the fire season, possibly because of warming in the boreal regions, could give rise to a feedback loop by shifting the timing (and increasing the magnitude) of the impacts on forest fires on Arctic climate.
Warneke, C., R. Bahreini, J. Brioude, C.A. Brock, J.A. de Gouw, D.W. Fahey, K.D. Froyd, J.S. Holloway, A. Middlebrook, L. Miller, S. Montzka, D.M. Murphy, J. Peischl, T.B. Ryerson, J.P. Schwarz, J.R. Spackman, and P. Veres, Biomass burning in Siberia and Kazakhstan as an important source for haze over the Alaskan Arctic in April 2008, Geophysical Research Letters, doi:10.1029/2008GL036194, 2009.