Characterization of Aerosol Hygroscopicity Over the Northeast Pacific Ocean: Impacts on Prediction of CCN and Stratocumulus Cloud Droplet Number Concentrations
AuthorSchulze, B. C.
Charan, S. M.
Kenseth, C. M.
Bates, K. H.
Metcalf, A. R.
Jonsson, H. H.
Flagan, R. C.
Seinfeld, J. H.
AffiliationUniv Arizona, Dept Chem & Environm Engn
Univ Arizona, Dept Hydrol & Atmospher Sci
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationSchulze, B. C., Charan, S. M., Kenseth, C. M., Kong, W., Bates, K. H., Williams, W., ... & Seinfeld, J. H. (2020). Characterization of aerosol hygroscopicity over the Northeast Pacific Ocean: Impacts on prediction of CCN and stratocumulus cloud droplet number concentrations. Earth and Space Science, 7(7), e2020EA001098.
JournalEARTH AND SPACE SCIENCE
Rights© 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License.
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AbstractDuring the Marine Aerosol Cloud and Wildfire Study (MACAWS) in June and July of 2018, aerosol composition and cloud condensation nuclei (CCN) properties were measured over the N.E. Pacific to characterize the influence of aerosol hygroscopicity on predictions of ambient CCN and stratocumulus cloud droplet number concentrations (CDNC). Three vertical regions were characterized, corresponding to the marine boundary layer (MBL), an above-cloud organic aerosol layer (AC-OAL), and the free troposphere (FT) above the AC-OAL. The aerosol hygroscopicity parameter (kappa) was calculated from CCN measurements (kappa(CCN)) and bulk aerosol mass spectrometer (AMS) measurements (kappa(AMS)). Within the MBL, measured hygroscopicities varied between values typical of both continental environments (similar to 0.2) and remote marine locations (similar to 0.7). For most flights, CCN closure was achieved within 20% in the MBL. For five of the seven flights, assuming a constant aerosol size distribution produced similar or better CCN closure than assuming a constant "marine" hygroscopicity (kappa = 0.72). An aerosol-cloud parcel model was used to characterize the sensitivity of predicted stratocumulus CDNC to aerosol hygroscopicity, size distribution properties, and updraft velocity. Average CDNC sensitivity to accumulation mode aerosol hygroscopicity is 39% as large as the sensitivity to the geometric median diameter in this environment. Simulations suggest CDNC sensitivity to hygroscopicity is largest in marine stratocumulus with low updraft velocities (<0.2 m s(-1)), where accumulation mode particles are most relevant to CDNC, and in marine stratocumulus or cumulus with large updraft velocities (>0.6 m s(-1)), where hygroscopic properties of the Aitken mode dominate hygroscopicity sensitivity.
NoteOpen access article
VersionFinal published version
Except where otherwise noted, this item's license is described as © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License.