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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 16
Atmos. Chem. Phys., 18, 12477-12489, 2018
https://doi.org/10.5194/acp-18-12477-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 12477-12489, 2018
https://doi.org/10.5194/acp-18-12477-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Aug 2018

Research article | 28 Aug 2018

Cloud droplet activation of black carbon particles coated with organic compounds of varying solubility

Maryam Dalirian1, Arttu Ylisirniö2, Angela Buchholz2, Daniel Schlesinger1, Johan Ström1, Annele Virtanen2, and Ilona Riipinen1 Maryam Dalirian et al.
  • 1Department of Environmental Science and Analytical Chemistry (ACES) and the Bolin Centre for Climate research, Stockholm University, Stockholm, Sweden
  • 2Department of Applied Physics, University of Eastern Finland, Kuopio, Finland

Abstract. Atmospheric black carbon (BC) particles are a concern due to their impact on air quality and climate. Their net climate effect is, however, still uncertain. This uncertainty is partly related to the contribution of coated BC particles to the global cloud condensation nuclei (CCN) budgets. In this study, laboratory measurements were performed to investigate CCN activity of BC (REGAL 400R pigment black) particles, in pure state or coated through evaporating and subsequent condensation of glutaric acid, levoglucosan (both water-soluble organics) or oleic acid (an organic compound with low solubility). A combination of soot particle aerosol mass spectrometer (SP-AMS) measurements and size distribution measurements with a scanning mobility particle sizer (SMPS) showed that the studied BC particles were nearly spherical agglomerates with a fractal dimension of 2.79 and that they were coated evenly by the organic species. The CCN activity of BC particles increased after coating with all the studied compounds and was governed by the fraction of organic material. The CCN activation of the BC particles coated by glutaric acid and levoglucosan were in good agreement with the theoretical calculations using the shell-and-core model, which is based on a combination of the CCN activities of the pure compounds. The oleic acid coating enhanced the CCN activity of the BC particles, even though the pure oleic acid particles were CCN inactive. The surprising effect of oleic acid might be related to the arrangement of the oleic acid molecules on the surface of the BC cores or other surface phenomena facilitating water condensation onto the coated particles. Our results show that present theories have potential for accurately predicting the CCN activity of atmospheric BC coated with organic species, given that the identities and amounts of the coating species are known. Furthermore, our results suggest that even relatively thin soluble coatings (around 2nm for the compounds studied here) are enough to make the insoluble BC particles CCN active at typical atmospheric supersaturations and thus be efficiently taken up by cloud droplets. This highlights the need for an accurate description of the composition of atmospheric particles containing BC to unravel their net impact on climate.

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Atmospheric black carbon (BC) particles are a concern due to their impact on air quality and climate. Their net climate effect is, however, still uncertain. In this study, laboratory measurements were performed to investigate cloud condensation nuclei (CCN) activity of BC particles, in pure state or coated by various organic species. Our results show that existing theories have potential in describing the CCN activation of atmospheric BC mixed with soluble pollutants.
Atmospheric black carbon (BC) particles are a concern due to their impact on air quality and...
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