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Published May 16, 2015 | Published + Supplemental Material
Journal Article Open

Primary marine aerosol-cloud interactions off the coast of California


Primary marine aerosol (PMA)-cloud interactions off the coast of California were investigated using observations of marine aerosol, cloud condensation nuclei (CCN), and stratocumulus clouds during the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) and the Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets (SOLEDAD) studies. Based on recently reported measurements of PMA size distributions, a constrained lognormal-mode-fitting procedure was devised to isolate PMA number size distributions from total aerosol size distributions and applied to E-PEACE measurements. During the 12 day E-PEACE cruise on the R/V Point Sur, PMA typically contributed less than 15% of total particle concentrations. PMA number concentrations averaged 12 cm^(−3) during a relatively calmer period (average wind speed 12 m/s^1) lasting 8 days, and 71 cm^(−3) during a period of higher wind speeds (average 16 m/s^1) lasting 5 days. On average, PMA contributed less than 10% of total CCN at supersaturations up to 0.9% during the calmer period; however, during the higher wind speed period, PMA comprised 5–63% of CCN (average 16–28%) at supersaturations less than 0.3%. Sea salt was measured directly in the dried residuals of cloud droplets during the SOLEDAD study. The mass fractions of sea salt in the residuals averaged 12 to 24% during three cloud events. Comparing the marine stratocumulus clouds sampled in the two campaigns, measured peak supersaturations were 0.2 ± 0.04% during E-PEACE and 0.05–0.1% during SOLEDAD. The available measurements show that cloud droplet number concentrations increased with >100 nm particles in E-PEACE but decreased in the three SOLEDAD cloud events.

Additional Information

© 2015 American Geophysical Union. Received 8 Dec 2014; Accepted 13 Apr 2015; Accepted article online 16 Apr 2015; Published online 14 May 2015. This work was funded by NSF AGS-1360645, NSF AGS-1013423, NSF AGS-1008848, DOE DE-SC0006679, and ONR grants N00014-11-1-0783, N00014-10-1-0200, and N00014-10-1-0811. R.L.M. appreciates the support of the Scripps Postdoctoral Scholars program. We gratefully acknowledge the help and support of the crew and staff of the R/V Point Sur and the CIRPAS Twin Otter, as well as assistance from Janin Guzman-Morales, Ashley Corrigan, Bill Shull, and Ken Duff of Scripps Institution of Oceanography. To obtain the data used in this study please go to http://goo.gl/3lWlJz or contact the corresponding author (lmrussell@ucsd.edu).

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Published - jgrd52157.pdf

Supplemental Material - jgrd52157-sup-0001-Supplementary.doc


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