Preprints
https://doi.org/10.5194/acp-2021-22
https://doi.org/10.5194/acp-2021-22

  22 Jan 2021

22 Jan 2021

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Large hemispheric difference in ultrafine aerosol concentrations in the lowermost stratosphere at mid and high latitudes

Christina J. Williamson1,2, Agnieszka Kupc2,3, Andrew Rollins2, Jan Kazil1,2, Karl D. Froyd1,2, Eric A. Ray1,2, Daniel M. Murphy2, Gregory P. Schill1,2, Jeff Peischl1,2, Chelsea Thompson1,2, Ilann Bourgeois1,2, Thomas Ryerson2,a, Glenn S. Diskin4, Joshua P. DiGangi4, Donald R. Blake5, Thao Paul V. Bui6, Maximilian Dollner3, Bernadett Weinzierl3, and Charles A. Brock2 Christina J. Williamson et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, U.S.A.
  • 2Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, U.S.A
  • 3Faculty of Physics, Aerosol Physics and Environmental Physics, University of Vienna, 1090 Vienna, Austria
  • 4NASA Langley Research Center, Hampton, VA 23681, USA
  • 5Department of Chemistry, University of California Irvine, Irvine, CA 92697, U.S.A.
  • 6Earth Science Division, NASA Ames Research Center, Moffett Field, California, U.S.A.
  • anow at: Scientific Aviation, Boulder, CO 80301, U.S.A.

Abstract. The details of aerosol processes and size distributions in the stratosphere are important for both heterogeneous chemistry and aerosol-radiation interactions. Using in-situ, global-scale measurements of the size distribution of particles with diameters > 3 nm from the NASA Atmospheric Tomography Mission (ATom), we identify a mode of ultrafine aerosol in the lowermost stratosphere (LMS) at mid and high latitudes. This mode is substantial only in the northern hemisphere (NH), and was observed in all four seasons. We also observe elevated SO2, an important precursor for new particle formation (NPF) and growth, in the NH LMS. We use box modelling and thermodynamic calculations to show that NPF can occur in the LMS conditions observed on ATom. Aircraft emissions are shown as likely sources of this SO2, as well as a potential source of ultrafine particles directly emitted by, or formed in the plume of the engines. These ultra-fine particles have the potential to grow to larger sizes, and to coagulate with larger aerosol, affecting heterogeneous chemistry and aerosol-radiation interactions. Understanding all sources and characteristics of stratospheric aerosol is important in the context of anthropogenic climate change as well as proposals for climate intervention via stratospheric sulphur injection. This analysis not only adds to the, currently sparse, observations of the global impact of aviation, but also introduces another aspect of climate influence, namely a size distribution shift of the background aerosol distribution in the LMS.

Christina J. Williamson et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee comment', Anonymous Referee #1, 11 Feb 2021
    • AC1: 'Reply on RC1', Christina Williamson, 16 Mar 2021
  • RC2: 'Comment on acp-2021-22', Anonymous Referee #2, 01 Mar 2021
    • AC2: 'Reply on RC2', Christina Williamson, 16 Mar 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee comment', Anonymous Referee #1, 11 Feb 2021
    • AC1: 'Reply on RC1', Christina Williamson, 16 Mar 2021
  • RC2: 'Comment on acp-2021-22', Anonymous Referee #2, 01 Mar 2021
    • AC2: 'Reply on RC2', Christina Williamson, 16 Mar 2021

Christina J. Williamson et al.

Christina J. Williamson et al.

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Short summary
Aerosols in the stratosphere influence climate by scattering and absorbing sunlight, and through chemical reactions occurring on the particles' surfaces. We observed more ultrafine aerosol particles (small aerosols, with diameters below 12 nm) in the mid and high latitude lowermost stratosphere (8–13 km) in the northern than the southern hemisphere. The most likely cause of this is aircraft emissions, which are concentrated in the northern hemisphere at similar altitudes to our observations.
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