|Title||Primary marine aerosol-cloud interactions off the coast of California|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||Modini RL, Frossard AA, Ahlm L, Russell LM, Corrigan CE, Roberts GC, Hawkins L.N, Schroder JC, Bertram A.K, Zhao R., Lee A.KY, Abbatt J.PD, Lin J., Nenes A, Wang Z, Wonaschutz A, Sorooshian A, Noone K.J, Jonsson H, Seinfeld JH, Toom-Sauntry D, Macdonald A.M, Leaitch WR|
|Journal||Journal of Geophysical Research-Atmospheres|
|Type of Article||Article|
|Keywords||2011 e-peace; aerosol-cloud interactions; airborne measurements; boundary-layer; chemical-composition; cloud condensation nuclei; condensation nuclei; counterflow virtual impactor; droplet number concentrations; hygroscopic properties; marine aerosol; organic aerosol; sea spray aerosol; sea-spray aerosol; stratocumulus clouds; supersaturations|
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 12m/s(1)) lasting 8 days, and 71cm(-3) during a period of higher wind speeds (average 16m/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 0.20.04% 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.
"The net effect of a change in the number of available cloud condensation nuclei (CCN) on cloud droplet number concentrations depends on the CCN distribution and the dynamics of the cloud. Examination of the dependence of cloud droplet number concentrations (CDNC) on precursor aerosol concentrations as a function of in-cloud sea-salt levels suggests that primary marine aerosol (PMA) had a positive impact on the cloud droplet number concentrations of the marine stratocumulus clouds probed during the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). However, PMA particles may have contributed to the reduction in CDNC with increasing >100 nm particles in the three clouds sampled during Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets (SOLEDAD), since supersaturation can be reduced by rapid water vapor depletion by coarse PMA particles."