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Published August 16, 2010 | Published
Journal Article Open

Observation of playa salts as nuclei in orographic wave clouds


During the Ice in Clouds Experiment-Layer Clouds (ICE-L), dry lakebed, or playa, salts from the Great Basin region of the United States were observed as cloud nuclei in orographic wave clouds over Wyoming. Using a counterflow virtual impactor in series with a single-particle mass spectrometer, sodium-potassium-magnesium-calcium-chloride salts were identified as residues of cloud droplets. Importantly, these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei (CCN) efficiencies close to sea salt. Using a suite of chemical characterization instrumentation, the playa salts were observed to be internally mixed with oxidized organics, presumably produced by cloud processing, as well as carbonate. These salt particles were enriched as residues of large droplets (>19 μm) compared to smaller droplets (>7 μm). In addition, a small fraction of silicate-containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes. While the high CCN activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments, this study provides direct evidence of the importance of playa salts in cloud formation in continental North America has not been shown previously. Studies are needed to model and quantify the impact of playas on climate globally, particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes.

Additional Information

© 2010 American Geophysical Union. Received 10 December 2009; accepted 22 March 2010; published 3 August 2010. The authors thank the ICE‐L C‐130 crew and investigators for their support. NSF and NCAR are acknowledged for financial support of the ICE‐L field campaign, as well as the work of A.J. Heymsfield and D.C. Rogers. K.A. Pratt, C.J. Gaston, and K.A. Prather acknowledge NSF for support of ICE‐L (ATM‐0650659), laboratory studies (ATM‐0650659 and ATM‐0625526), A‐ATOFMS development (ATM‐0321362), and a graduate research fellowship for K.A. Pratt. C.H. Twohy and P.J. DeMott acknowledge NSF for ICE‐L support (ATM‐0612605 and ATM‐0611936, respectively). S.M. Murphy and J.H. Seinfeld acknowledge NSF for support of ICE‐L (ATM‐0340832) and NASA for an Earth and Space Sciences Fellowship for S.M. Murphy. R.C. Moffet, T.R. Henn, and M.K. Gilles acknowledge support from the Department of Energy's Office of Biological and Environmental Research, Atmospheric Science Program, and Office of Basic Energy Sciences (DE‐AC02‐05CH11231), as well as the Lawrence Berkeley National Laboratory Glenn T. Seaborg Fellowship for R.C. Moffet. STEM‐EDX was completed by Julia Sobolik (Oregon State University) and Traci Lersch (RJ LeeGroup, Inc). Cloud probe data were provided by NCAR/EOL under sponsorship of NSF (http://data.eol.ucar.edu). Total PM10 and PM2.5 mass concentrations in Utah were provided by the Utah State Division of Air Quality. Gregory Roberts (UCSD) is thanked for use of the CCNc. David Soller and Marith Reheis (USGS) are acknowledged for provision of the playa sediments map. ICE‐L lidar and radar data were provided by Zhien Wang, Jeffrey French, and Samuel Haimov (University of Wyoming). Sonia Kreidenweis (Colorado State University) and Trude Eidhammer (NCAR) are thanked for discussions. The authors acknowledge NOAA ARL for the provision of the HYSPLIT EADY website (http://www.arl.noaa.gov/ready.html) used in this publication. Salt Lake City radiosonde data were provided by the University of Wyoming; surface wind data were provided by MesoWest.

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