Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 11107-11124, 2016
https://doi.org/10.5194/acp-16-11107-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
08 Sep 2016
Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic
W. Richard Leaitch1, Alexei Korolev1, Amir A. Aliabadi1,a, Julia Burkart2, Megan D. Willis2, Jonathan P. D. Abbatt2, Heiko Bozem3, Peter Hoor3, Franziska Köllner4, Johannes Schneider4, Andreas Herber5, Christian Konrad5, and Ralf Brauner6 1Environment and Climate Change Canada, Toronto, Canada
2Department of Chemistry, University of Toronto, Toronto, Canada
3Institute for Atmospheric Physics, University of Mainz, Mainz, Germany
4Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
5Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
6Department of Maritime and Logistics Studies, Jade University, Elsfleth, Germany
anow at: Environmental Engineering, University of Guelph, Guelph, Canada
Abstract. Observations addressing effects of aerosol particles on summertime Arctic clouds are limited. An airborne study, carried out during July 2014 from Resolute Bay, Nunavut, Canada, as part of the Canadian NETCARE project, provides a comprehensive in situ look into some effects of aerosol particles on liquid clouds in the clean environment of the Arctic summer. Median cloud droplet number concentrations (CDNC) from 62 cloud samples are 10 cm−3 for low-altitude cloud (clouds topped below 200 m) and 101 cm−3 for higher-altitude cloud (clouds based above 200 m). The lower activation size of aerosol particles is  ≤  50 nm diameter in about 40 % of the cases. Particles as small as 20 nm activated in the higher-altitude clouds consistent with higher supersaturations (S) for those clouds inferred from comparison of the CDNC with cloud condensation nucleus (CCN) measurements. Over 60 % of the low-altitude cloud samples fall into the CCN-limited regime of Mauritsen et al. (2011), within which increases in CDNC may increase liquid water and warm the surface. These first observations of that CCN-limited regime indicate a positive association of the liquid water content (LWC) and CDNC, but no association of either the CDNC or LWC with aerosol variations. Above the Mauritsen limit, where aerosol indirect cooling may result, changes in particles with diameters from 20 to 100 nm exert a relatively strong influence on the CDNC. Within this exceedingly clean environment, as defined by low carbon monoxide and low concentrations of larger particles, the background CDNC are estimated to range between 16 and 160 cm−3, where higher values are due to activation of particles  ≤  50 nm that likely derive from natural sources. These observations offer the first wide-ranging reference for the aerosol cloud albedo effect in the summertime Arctic.

Citation: Leaitch, W. R., Korolev, A., Aliabadi, A. A., Burkart, J., Willis, M. D., Abbatt, J. P. D., Bozem, H., Hoor, P., Köllner, F., Schneider, J., Herber, A., Konrad, C., and Brauner, R.: Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic, Atmos. Chem. Phys., 16, 11107-11124, https://doi.org/10.5194/acp-16-11107-2016, 2016.
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Short summary
Thought to be mostly unimportant for summertime Arctic liquid-water clouds, airborne observations show that atmospheric aerosol particles 50 nm in diameter or smaller and most likely from natural sources are often involved in cloud formation in the pristine Arctic summer. The result expands the reference for aerosol forcing of climate. Further, for extremely low droplet concentrations, no evidence is found for a connection between cloud liquid water and aerosol particle concentrations.
Thought to be mostly unimportant for summertime Arctic liquid-water clouds, airborne...
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