Atmos. Chem. Phys. Discuss., 11, 1543-1594, 2011
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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.
Absorbing aerosol in the troposphere of the Western Arctic during the 2008 ARCTAS/ARCPAC airborne field campaigns
C. S. Mc Naughton1, A. D. Clarke1, S. Freitag1, V. N. Kapustin1, Y. Kondo2, N. Moteki2, L. Sahu2, N. Takegawa2, J. P. Schwarz3, J. R. Spackman3, L. Watts3, G. Diskin4, J. Podolske5, J. S. Holloway3, A. Wisthaler6, T. Mikoviny6, J. de Gouw3, C. Warneke3,7, J. Jimenez7, M. Cubison7, S. G. Howell1, A. Middlebrook3, R. Bahreini3, B. E. Anderson4, E. Winstead4, K. L. Thornhill4, D. Lack3, J. Cozic3, and C. A. Brock3
1School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI, USA
2Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan
3Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
4NASA Langley Research Center, Hampton, VA, USA
5NASA Ames Research Center, Moffett Field, CA, USA
6Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
7Cooperative Institute for Research in Environmental Sciences (CIRES) University of Colorado, Boulder, USA

Abstract. In the spring of 2008 NASA and NOAA funded the ARCTAS and ARCPAC field campaigns as contributions to POLARCAT, a core IPY activity. During the campaigns the NASA DC-8, P-3B and NOAA WP-3D aircraft conducted over 150 h of in-situ sampling between 0.1 and 12 km throughout the Western Arctic north of 55° N (i.e. Alaska to Greenland). All aircraft were equipped with multiple wavelength measurements of aerosol optics, trace gas and aerosol chemistry measurements, as well as direct measurements of black carbon mass and the aerosol size distribution. Late April of 2008 proved to be exceptional in terms of Asian biomass burning emissions transported to the Western Arctic. Though these smoke plumes account for only 11–14% of the samples within the Western Arctic domain, they account for 43–47% of the total burden of black carbon. Light absorbing carbon from urban/industrial activities and biomass burning together account for 93–98% of total light absorption in the middle troposphere. Light absorption by mineral dust accounts for the remaining absorption in the middle troposphere, but up to 14% near the surface and in the upper troposphere below the tropopause. Stratifying the data to reduce the influence of dust allows us to determine mass absorption efficiencies for black carbon of 11.2±0.8, 9.5±0.6 and 7.4±0.7 m2 g−1 at 470, 530 and 660 nm wavelengths. These estimates are consistent with 35–80% enhancements in 530 nm absorption due to clear or slightly absorbing coatings of pure black carbon particulate. Assuming a 1/λ wavelength dependence for BC absorption, and assuming that refractory aerosol (420 °C, τ = 0.1 s) in low-dust samples is dominated by brown carbon, we derive mass absorption efficiencies for brown carbon of 0.83±0.15 and 0.27±0.08 m2 g−1 at 470 and 530 nm wavelengths. Estimates for the mass absorption efficiencies of Asian Dust are 0.034 m2 g−1 and 0.017 m2 g−1. However the values are highly uncertain due to the limitations imposed by PSAP instrument noise. In-situ ARCTAS/ARCPAC measurements during the IPY provide valuable constraints for absorbing aerosol over the Western Arctic, species which are currently poorly simulated over a region that is critically under-sampled.

Citation: Mc Naughton, C. S., Clarke, A. D., Freitag, S., Kapustin, V. N., Kondo, Y., Moteki, N., Sahu, L., Takegawa, N., Schwarz, J. P., Spackman, J. R., Watts, L., Diskin, G., Podolske, J., Holloway, J. S., Wisthaler, A., Mikoviny, T., de Gouw, J., Warneke, C., Jimenez, J., Cubison, M., Howell, S. G., Middlebrook, A., Bahreini, R., Anderson, B. E., Winstead, E., Thornhill, K. L., Lack, D., Cozic, J., and Brock, C. A.: Absorbing aerosol in the troposphere of the Western Arctic during the 2008 ARCTAS/ARCPAC airborne field campaigns, Atmos. Chem. Phys. Discuss., 11, 1543-1594, doi:10.5194/acpd-11-1543-2011, 2011.
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