Preprints
https://doi.org/10.5194/acp-2021-1101
https://doi.org/10.5194/acp-2021-1101
 
14 Feb 2022
14 Feb 2022
Status: this preprint is currently under review for the journal ACP.

Ice-Nucleating Particles Near Two Major Dust Source Regions

Charlotte M. Beall1,2, Thomas C. J. Hill3, Paul J. DeMott3, Tobias Köneman2,a, Michael Pikridas4, Frank Drewnick5, Hartwig Harder6, Christopher Pöhlker2, Jos Lelieveld4,6, Bettina Weber2,b, Minas Iakovides4, Roman Prokeš7,8, Jean Sciare4, Meinrat O. Andreae1,2,9, M. Dale Stokes1, and Kimberly A. Prather1,10 Charlotte M. Beall et al.
  • 1Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
  • 2Max Planck Institute for Chemistry, Multiphase Chemistry and Biogeochemistry Departments, D-55128 Mainz, Germany
  • 3Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA
  • 4Climate & Atmosphere Research Center, The Cyprus Institute, Nicosia, CY-1645, Cyprus
  • 5Max Planck Institute for Chemistry, Particle Chemistry Department, D-55128 Mainz, Germany
  • 6Max Planck Institute for Chemistry, Atmospheric Chemistry Department, D-55128 Mainz, Germany
  • 7RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno, Czech Republic
  • 8Department of Atmospheric Matter Fluxes and Long-range Transport, Global Change Research Institute of the Czech Academy of Sciences, Belidla 4a, 60300, Brno, Czech Republic
  • 9Department of Geology and Geophysics, King Saud University, Riyadh, Saudi Arabia
  • 10Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093 USA
  • anow at: Envicontrol GmbH, Waidmarkt 11, 50676 Köln, Germany
  • bnow at: Institute of Biology, University of Graz, 8010 Graz, Austria

Abstract. Mineral dust and sea spray aerosol represent important sources of ice nucleating particles (INPs), the minor fraction of aerosol particles able to trigger cloud ice crystal formation and, consequently, influence multiple climate-relevant cloud properties including lifetime, reflectivity, and precipitation efficiency. Mineral dust is considered the dominant INP source in many parts of the world due to its ice nucleation efficiency and its sheer abundance, with global emission rates of up to 4700 Tg a−1. However, INPs emitted from the ocean surface in sea spray aerosol frequently dominate INP populations in remote marine environments, including parts of the Southern Ocean where cloud-resolving model simulations have demonstrated that cloud reflectivity is likely strongly controlled by INPs. Here we report INP concentrations measured in aerosol and seawater samples during Air Quality and Climate Change in the Arabian BAsin (AQABA), a shipborne campaign that spanned the Red Sea, Gulf of Aden, Arabian Sea, Arabian Gulf, and part of the Mediterranean. In aerosol samples collected within a few hundred kilometers of the first and second ranked sources of dust globally, the Sahara and Arabian Peninsula, INP concentrations ranged from 0.2 to 11 L−1 at −20 °C with observed ice nucleation site densities (ns) 1–3 orders of magnitude below levels predicted by mineral dust INP parameterizations. Over half of the samples (at least 14 of 26) were collected during dust storms with average dust mass concentrations between 150 and 490 μg m−3 (PM10). The impacts of heat and peroxide treatments indicate that organics were responsible for the observed ice nucleation (IN) -activity at temperatures ≥ −15 °C with proteinaceous (heat-labile) INPs frequently observed at higher freezing temperatures > −10 °C. Overall, results demonstrate that despite proximity to the Sahara and the Arabian Peninsula and the dominance of mineral dust in the aerosol sampled, existing mineral dust parameterizations alone would not skillfully represent the near-surface ns in the observed temperature regime (−6 to −25 °C). The decreased ns, and results demonstrating that organics dominated the observed IN activity > −15 °C, indicate that the IN-active organic species are limited compared to the mineral IN components of dust. Future efforts to develop or improve representations of dust INPs at modest supercooling (> −15 °C) would benefit from a characterization of the specific organic species associated with dust INPs. More generally, an improved understanding of the organic species associated with increased IN -activity and their variability across dust source regions would directly inform efforts to determine whether ns-based parameterizations are appropriate for faithful representation of dust INPs in this sensitive temperature regime, whether region-specific parameterizations are required, or whether an alternative to the ns approach is necessary.

Charlotte M. Beall et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-1101', Anonymous Referee #1, 04 Mar 2022
  • RC2: 'Comment on acp-2021-1101', Anonymous Referee #2, 19 Mar 2022
  • RC3: 'Comment on acp-2021-1101', Anonymous Referee #3, 29 Mar 2022

Charlotte M. Beall et al.

Data sets

Data from: Ice-nucleating particles near two major dust source regions Beall, Charlotte, M.; Hill, Thomas, C. J.; DeMott, Paul J.; Könemann, Tobias; Pikridas, Michael; Drewnick, Frank; Harder, Hartwig; Pöhlker, Christopher; Lelieveld, Jos; Weber, Bettina; Iakovides, Minas; Prokes, Roman; Sciare, Jean; Andreae, Meinrat O.; Stokes, M. Dale; Prather, Kimberly A. https://doi.org/10.6075/J0X0676P

Charlotte M. Beall et al.

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Short summary
Ice-nucleating particles (INPs) are rare aerosols that can trigger ice formation in clouds and affect multiple climate-relevant cloud properties such as phase, reflectivity and lifetime. Dust is the dominant INP source, yet few measurements have been reported near major dust sources. Here we report INP observations within 100s of km of the two biggest dust source regions globally: the Sahara and the Arabian Peninsula. Results show that at temperatures > −15 °C, INPs are dominated by organics.
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