References

ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

1680-7375

Copernicus GmbH

Göttingen, Germany

10.5194/acpd-11-21789-2011

Hygroscopicity and composition of Alaskan Arctic CCN during April 2008

Moore

R. H.

¹ Bahreini

² ³ Brock

C. A.

² Froyd

K. D.

² ³ Cozic

² ³ ⁵ Holloway

J. S.

² ³ Middlebrook

A. M.

² Murphy

D. M.

² Nenes

¹ ⁴

School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA

Earth Systems Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA

School of Earth & Atmospheric Sciences, Georgia Inst. of Technology, Atlanta, Georgia, USA

now at: Laboratoire de Glaciologie et Géophysique de l'Environnement, Grenoble, France

03 08 2011

11 8 21789 21834

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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We present a comprehensive characterization of cloud condensation nuclei (CCN) sampled in the Alaskan Arctic during the 2008 Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project, a component of the POLARCAT and International Polar Year (IPY) initiatives. Four distinct air mass types were sampled including relatively pristine Arctic background conditions as well as biomass burning and anthropogenic pollution plumes. Despite differences in chemical composition, inferred aerosol hygroscopicities were fairly invariant and ranged from κ = 0.1–0.3 over the atmospherically-relevant range of water vapor supersaturations studied. Analysis of the individual mass spectral m/z 43 and 44 peaks from an aerosol mass spectrometer show the organic aerosols sampled to be well-oxygenated, consistent with with long-range transport and aerosol aging processes. However, inferred hygroscopicities are less than would be predicted based on previous parameterizations of biogenic oxygenated organic aerosol, suggesting an upper limit on organic aerosol hygroscopicity above which κ is less sensitive to the O:C ratio. Most Arctic aerosol act as CCN above 0.1 % supersaturation, although the data suggest the presence of an externally-mixed, non-CCN-active mode comprising approximately 0–20 % of the aerosol number. CCN closure was assessed using measured size distributions, bulk chemical composition measurements, and assumed aerosol mixing states; CCN predictions tended toward overprediction, with the best agreement (± 0–20 %) obtained by assuming the aerosol to be externally-mixed with soluble organics. Closure also varied with CCN concentration, and the best agreement was found for CCN concentrations above 100 cm−3 with a 1.5- to 3-fold overprediction at lower concentrations.

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