Preprints
https://doi.org/10.5194/acp-2021-899
https://doi.org/10.5194/acp-2021-899

  29 Nov 2021

29 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Characterizing the hygroscopicty of growing particles in the Canadian Arctic summer

Rachel Y.-W. Chang1, Jonathan P. D. Abbatt2, Matthew C. Boyer1,a, Jai Prakash Chaubey1, and Douglas B. Collins2,b Rachel Y.-W. Chang et al.
  • 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
  • 2Department of Chemistry, University of Toronto, Toronto, Ontario M5T 1T6, Canada
  • anow at: Institute for Atmospheric and Earth System Research, INAR/Physics, University of Helsinki, Finland
  • bnow at: Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, USA

Abstract. The impact of aerosols on clouds is a well-studied, although still poorly constrained, part of the atmospheric system. New particle formation (NPF) is thought to contribute 40–80 % of the global cloud droplet number concentration, although it is extremely difficult to observe an air mass from NPF to cloud formation. NPF and growth occurs frequently in the Canadian Arctic summer atmosphere, although only a few studies have characterized the source and properties of these aerosols. This study presents cloud condensation nuclei (CCN) concentrations measured on board the CCGS Amundsen in the eastern Canadian Arctic Archipelago from 23 July to 23 August 2016 as part of the Network on Climate and Aerosols: Addressing Uncertainties in Remote Canadian Environments (NETCARE). The study was dominated by frequent ultrafine particle and/or growth events, and particles smaller than 100 nm dominated the size distribution for 92 % of the study period. Using κ-Kohler theory and aerosol size distributions, the mean hygroscopicity parameter (κ) calculated for the entire study was 0.12 (0.06–0.12, 25th–75th percentile), suggesting that the condensable vapours that led to particle growth were primarily non-hygroscopic, which we infer to be organic. Based on past measurement and modelling studies from NETCARE and the Canadian Arctic, it seems likely that the source of these non-hygroscopic, organic, vapours is the ocean. Examining specific growth events suggests that the mode diameter (Dmax) had to exceed 40 nm before CCN concentrations at 0.99 % SS started to increase, although a statistical analysis shows that CCN concentrations increased 13–274 cm−3 during all ultrafine particle and/or growth times (total particle concentrations > 500 cm−3, Dmax < 100 nm) compared to Background times (total concentrations < 500 cm−3) at SS of 0.26–0.99 %. This value increased to 25–425 cm−3 if the growth times were limited to times when Dmax was also larger than 40 nm. These results support past results from NETCARE by showing that the frequently observed ultrafine particle and growth events are dominated by a highly non-hygroscopic fraction, which we interpret to be organic vapours originating from the ocean, and that these growing particles can increase the background CCN concentrations at SS as low as 0.26 %, thus pointing to their potential contribution to cloud properties and thus climate through the radiation balance.

Rachel Y.-W. Chang et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Rachel Y.-W. Chang et al.

Rachel Y.-W. Chang et al.

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Short summary
During summer 2016, the ability of newly formed particles to turn into droplets was measured in the Canadian Arctic. Our observations suggest that these small particles were growing by the condensation of organic vapours, likely coming from the surrounding open waters. These particles grew large enough that they could form cloud droplets, and therefore affect the Earth’s radiation budget. These results are relevant as the Arctic summer rapidly warms with climate change.
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