Atmos. Chem. Phys. Discuss., 10, 15167-15196, 2010
www.atmos-chem-phys-discuss.net/10/15167/2010/
doi:10.5194/acpd-10-15167-2010
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Aircraft observations of enhancement and depletion of black carbon mass in the springtime Arctic
J. R. Spackman1,2, R. S. Gao1, W. D. Neff3, J. P. Schwarz1,2, L. A. Watts1,2, D. W. Fahey1,2, J. S. Holloway1,2, T. B. Ryerson1, J. Peischl1,2, and C. A. Brock1
1National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Chemical Sciences Division, Boulder, Colorado, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
3National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Physical Sciences Division, Boulder, Colorado, USA

Abstract. Understanding the processes controlling black carbon (BC) in the Arctic is crucial for evaluating the impact of anthropogenic and natural sources of BC on Arctic climate. Vertical profiles of BC mass were observed from the surface to near 7-km altitude in April 2008 using a Single-Particle Soot Photometer (SP2) during flights on the NOAA WP-3D research aircraft from Fairbanks, Alaska. These measurements were conducted during the NOAA-sponsored Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project as part of POLARCAT, an International Polar Year (IPY) activity. In the free troposphere, the Arctic air mass was influenced by long-range transport from biomass-burning and anthropogenic source regions at lower latitudes especially during the latter part of the campaign. Maximum average BC mass loadings of 150 ng kg−1 were observed near 5.5-km altitude in the aged Arctic air mass. In biomass-burning plumes, BC was enhanced from near the top of the Arctic boundary layer (ABL) to 5.5 km compared to the aged Arctic air mass. At the bottom of some of the profiles, positive vertical gradients in BC were observed in the vicinity of open leads in the sea-ice. BC mass loadings increased by about a factor of two across the boundary layer transition in the ABL in these cases while carbon monoxide (CO) remained constant, evidence for depletion of BC in the ABL. BC mass loadings were positively correlated with O3 in ozone depletion events (ODEs) for all the observations in the ABL suggesting that BC was removed by dry deposition of BC on the snow or ice because molecular bromine, Br2, which photolyzes and catalytically destroys O3, is thought to be released near the open leads in regions of ice formation. We estimate the deposition flux of BC mass to the snow using a box model constrained by the vertical profiles of BC in the ABL. The open leads may increase vertical mixing in the ABL and entrainment of pollution from the free troposphere possibly enhancing the deposition of BC to the snow.

Citation: Spackman, J. R., Gao, R. S., Neff, W. D., Schwarz, J. P., Watts, L. A., Fahey, D. W., Holloway, J. S., Ryerson, T. B., Peischl, J., and Brock, C. A.: Aircraft observations of enhancement and depletion of black carbon mass in the springtime Arctic, Atmos. Chem. Phys. Discuss., 10, 15167-15196, doi:10.5194/acpd-10-15167-2010, 2010.
 
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