Publication Date:
2015-04-18
Description:
Primary marine aerosol (PMA)-cloud interactions off the coast of California were investigated using observations of marine aerosol, 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 CDNC increased with 〉100 nm particles in E-PEACE but decreased in the three SOLEDAD cloud events.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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