Seminar

Abstract

Knowing the physical properties of aerosol particles over the oceans is important to predict their radiative effects. There is evidence that recently produced biogenic organic compounds in the surface ocean may significantly affect the physical properties of sea spray aerosol particles, in particular their size, number, and hygroscopicity. This would amount to a potentially large amount of control by ocean biota on the radiative balance over the oceans. Some model simulations and in situ observations indicate the effects could be significant. However, there exists large variability in reported measurements of the organic mass content of fresh sea spray, with e.g. some studies showing organic mass fractions around 50% for 0.4 µm diameter sea spray, and others showing values less than 10% at that diameter. It has been difficult to determine what values are representative, even for relatively well-studied regions like the North Atlantic. We have produced a dataset of sea spray organic mass fractions using the NOAA PALMS (Particle Analysis by Laser Mass Spectrometry) instrument from measurements made on the DC-8 during the four-season NASA ATom mission. This dataset takes advantage of the unique qualities of single particle observations and the extremely broad spatial coverage achieved during ATom to provide a particle size-resolved view from ~ 0.15-0.7 µm diameter that is essentially free of biases such as secondary organic aerosol and coastal biogeochemical features. We find that the average organic mass fraction of fresh sea spray aerosol is on the low end of reported values, with low seasonal variability, on the vary broad spatial scales considered. We infer that strong biological control of fresh submicron sea spray aerosol properties is most likely the exception rather than the rule. I will compare the results with previous observations and highlight some uncertainties that remain.

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Mike Lawler received his PhD from the University of California, Irvine, for work on the multiphase cycling of reactive halogens in marine air. His postdoctoral work focused on the formation and growth of new particles in the atmospheric boundary layer. Currently he is a research scientist at CU Boulder CIRES/NOAA Chemical Sciences Lab, where he uses single particle mass spectrometry to characterize the formation and transformation pathways of atmospheric aerosol, with a recent focus on the lower stratosphere.