11 Jul 2022
11 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Organic enrichment in droplet residual particles relative to out of cloud over the northwest Atlantic: Analysis of airborne ACTIVATE data

Hossein Dadashazar1, Andrea F. Corral1, Ewan Crosbie2,3, Sanja Dmitrovic4, Simon Kirschler5,6, Kayla McCauley7, Richard Moore2, Claire Robinson2,3, Joseph Schlosser1, Michael Shook2, K. Lee Thornhill2, Christiane Voigt5,6, Edward Winstead2,3, Luke Ziemba2, and Armin Sorooshian1,4,7 Hossein Dadashazar et al.
  • 1Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA
  • 2NASA Langley Research Center, Hampton, VA, USA
  • 3Science Systems and Applications, Inc., Hampton, VA, USA
  • 4James C. Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA
  • 5Institute of Atmospheric Physics, German Aerospace Center
  • 6Institute of Atmospheric Physics, University Mainz, Germany
  • 7Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA

Abstract. Cloud processing is known to generate aerosol species such as sulfate and secondary organic aerosol, yet there is a scarcity of airborne data to examine this issue. The NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) was designed to build an unprecedented dataset relevant to aerosol-cloud interactions with two coordinated aircraft over the northwest Atlantic, with aerosol mass spectrometer data used from four deployments between 2020–2021 to contrast aerosol composition below, in (using a counterflow virtual impactor), and above boundary layer clouds. Consistent features in all time periods of the deployments (January–March, May–June, August–September) include the mass fraction of organics and relative amount of oxygenated organics (m/z 44) relative to total organics (f44) increasing in droplet residuals relative to below and above cloud. Detailed analysis comparing data below and in cloud suggests a possible role for in-cloud aqueous processing in explaining such results. These results are important as other datasets (e.g., reanalysis) suggest that sulfate is both more abundant than organics (in contrast to this work) and more closely related to drop number concentrations in the winter when aerosol-cloud interactions are strongest; here we show that organics are more abundant than sulfate in the droplet residuals and that aerosol interaction with clouds potentially decreases particle hygroscopicity due to the significant jump in organic : sulfate ratio for droplet residuals relative to surrounding cloud-free air. These results are important in light of the growing importance of organics over the northwest Atlantic in recent decades relative to sulfate owing to the success of regulatory activity over the eastern United States to cut sulfur dioxide emissions.

Hossein Dadashazar et al.

Status: open (until 22 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-387', Anonymous Referee #1, 15 Jul 2022 reply
  • RC2: 'Comment on acp-2022-387', Anonymous Referee #2, 26 Jul 2022 reply

Hossein Dadashazar et al.

Hossein Dadashazar et al.


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Short summary
Multi-season airborne data over the northwest Atlantic show that organic mass fraction and the relative amount of oxygenated organics within that fraction are enhanced in droplet residual particles as compared to particles below and above cloud. In-cloud aqueous processing is shown to be a potential driver of this compositional shift in cloud. This implies that aerosol-cloud interactions in the region reduce aerosol hygroscopicity due to the jump in the organic : sulfate ratio in cloud.