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https://doi.org/10.5194/acp-2020-809
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-809
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  02 Sep 2020

02 Sep 2020

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This preprint is currently under review for the journal ACP.

The effects of morphology, mobility size and SOA material coating on the ice nucleation activity of black carbon in the cirrus regime

Cuiqi Zhang1,2, Yue Zhang3,4,5, Martin J. Wolf2, Leonid Nichman6, Chuanyang Shen2,7, Timothy B. Onasch4,5, Longfei Chen1, and Daniel J. Cziczo2,8,9 Cuiqi Zhang et al.
  • 1School of Energy and Power Engineering, Beihang University, Beijing, China
  • 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 3Department of Environmental Sciencesand Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
  • 4Aerodyne Research Incorporated, Billerica, MA 01821, USA
  • 5Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA
  • 6National Research Council Canada, Flight Research Laboratory, Ottawa, ON, K1V 9B4, Canada
  • 7Department of Atmospheric and Oceanic Sciences, Peking University, Beijing, China
  • 8Department of Civil and EnvironmentalEngineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 9Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA

Abstract. There is evidence that black carbon (BC) particles may affect cirrus formation and hence global climate by acting as potential ice nucleating particles (INPs) in the troposphere. Nevertheless, the ice nucleation (IN) ability of bare BC and BC coated with secondary organic aerosol (SOA) material remains uncertain. We have systematically examined the IN ability of 100–400 nm size-selected BC particles with different morphologies and different SOA coatings representative of anthropogenic (toluene and n-dodecane) and biogenic (β-caryophyllene) sources in the cirrus regime (−46 to −38 °C). Several aerosolized BC proxies were selected to represent different particle morphologies and oxidation levels. Atmospheric aging was further replicated with exposure of SOA-coated BC to OH. The results demonstrate that the 400 nm hydrophobic BC types nucleate ice only at or near the homogeneous freezing threshold (−42 to −46 ˚C). Deposition IN, as opposed to purely homogeneous freezing, was observed to occur for some BC types between 100–200 nm within the investigated temperature range. More fractal BC particles did not consistently act as superior deposition INPs over more spherical ones. SOA coating generated by oxidizing β-caryophyllene with O3 did not seem to affect BC IN ability. However, SOA coatings generated from OH oxidation of various organic species did exhibit higher IN onset supersaturation ratio with respect to ice (SSi) compared with bare BC particles, with toluene SOA coating showing an increase of SSi by 0.1–0.15 while still below the homogeneous threshold. n-dodecane and β-caryophyllene-derived SOA only froze in the homogeneous regime. We attribute the inhibition of IN ability to the filling of the pores on the BC surface by the SOA material coating. OH exposure levels of all SOA coating experiments, from an equivalent atmospheric 10 days to 90 days, did not render significant differences in IN potential. Our study suggests that BC particles with large sizes and/or oxidized surfaces generally exhibit better IN ability, and that the organic coating materials can inhibit ice formation.

Cuiqi Zhang et al.

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Short summary
Black carbon is considered the second most important global warming agent. However, the role of BC aerosol-cloud-climate interactions in cirrus formation remains highly uncertain. In this study, we demonstrate that black carbon particles articles with large sizes and/or oxidized surfaces generally exhibit better ice nucleation ability, and that the organic coating materials can inhibit ice formation.
Black carbon is considered the second most important global warming agent. However, the role of...
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