21 January 2015

Sources and Composition of Submicron Organic Mass in Marine Aerosol Particles

Summary

Atmospheric marine aerosol particles (aMA) influence cloud microphysical processes in marine regions in addition to scattering and absorbing solar radiation in the marine boundary layer. Organic constituents that mix with sea salts in aMA can modify the cooling effect those aerosols have on the planet. Researchers including DOE-supported scientists investigated the sources and composition of aMA with a range of physical and chemical measurements during five open-ocean research cruises and determined the characteristic functional group composition of aMA from five ocean regions. aMA includes natural emissions as well as man-made emissions (e.g. shipping and some coastal human-caused emissions). They classified samples meeting certain criteria as atmospheric primary marine aerosol (aPMA) and compared their composition with that of of generated primary marine aerosol (gPMA) and seawater organic matter. They showed:1)The aPMA is 65 ± 12% hydroxyl, 21 ± 9% alkane, 6 ± 6% amine, and 7 ± 8% carboxylic acid functional groups. 2)The organic composition of aPMA is nearly identical to model-generated ocean-derived aerosol particles from bubbled seawater, indicating that its composition is the direct consequence of the organic constituents of the seawater source. 3)While the seawater composition was nearly invariant across all three ocean regions studied and over a broad range of chlorophyll a concentrations, gPMA from productive seawater had a larger fraction of alkane functional groups (42 ± 9%) compared to gPMA from nonproductive seawater (22 ± 10%), perhaps due to the presence of surfactants in productive seawater that accumulate in the bubble film and so are more strongly enriched in generated aerosol. Understanding the composition and sources of the organic fraction in marine aerosol will help characterize the degree to which they contribute to current and future aerosol climate forcing. 

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Publications
2014.  "Sources and Composition of Submicron Organic Mass in Marine Aerosol Particles."  Journal of Geophysical Research Atmospheres 119(22): 12977-13003, doi:10.1002/2014JD021913.