Ocean-Derived Aerosol: Properties and Climate Impacts
David Kieber (Convener). State University of New York, Syracuse, NY (SUNY-ESF) USA. Contact: [email protected]
Lynn Russell (Co-convener). University of California San Diego, La Jolla, CA USA. Contact: [email protected]
Elizabeth Minor (Rapporteur). University of Minnesota, Duluth, MN USA. Contact: [email protected]
The marine aerosol discussion session, with 90+ participants, was introduced with a brief update on the marine
aerosol midterm strategy. This included an announcement of an upcoming aerosol workshop
http://www4.ncsu.edu/~nmeskhi/Marine_Aerosol_Workshop/WEBSITE.html), mention of recent papers
highlighting the importance of marine aerosols (Quinn and Bates, Nature, 2011; de Leeuw et al., Rev. Geophys.,
2011), and a reminder of the key research questions and uncertainties in the marine aerosol midterm strategy
outlined in the aerosol white paper (http://solas-int.org/mts/research-strategy-2.html)
Following the brief introduction, an open discussion ensued that focused on several aspects related to organic
matter in marine aerosol during which several important questions were raised and debated.
(1) What is the best approach to study primary marine aerosol? Should ambient aerosols be studied directly or
should investigators generate primary marine aerosols? If studying the marine contribution to ambient aerosol,
how can the marine source function be teased out since marine aerosols will change rapidly with respect to pH,
chemical composition, water content, oxidant concentrations, etc.?
(2) How are marine dissolved and particulate organic matter related to the organic matter injected into the
atmosphere as primary marine aerosol? Fractionation of marine organic matter (OM) due to bubble bursting is
poorly constrained, and there little understanding of how much the surface microlayer impacts marine aerosol
organic matter production. This is compounded by the fact that, in general, more than 50% of marine OM is
uncharacterized, although this proportion is likely to be significantly reduced due to recent advances in sampling
technology (e.g., reverse osmosis/electrodialysis approaches).
(3) How can what is likely to be a complex composition of organic matter in marine aerosol be deconvolved,
especially in the submicron fraction? This is a critical question that is not expected to be easily resolved because of
uncertainties related to the marine source function and the
degree to which there is fractionation of marine organic matter during the bubble bursting process.
(4) Are oceanographers and atmospheric scientists on the same page with respect to some key terminology
including (a) water soluble versus insoluble OM, (b) gels and exopolysaccharides (EPS), and (c) hydrophobic
versus hydrophilic. Finally, there was some discussion regarding analytical techniques associated with generating,
collecting and analyzing primary marine aerosol. In particular,
(5) Is the organic composition chemically altered when collecting ambient aerosol or generating marine aerosol?
(6) What are the best approaches to analyze marine aerosol? FTIR, NMR, MS, UV-Vis etc. each have their own
advantages and limitations, but together they should render a fairly comprehensive view of organic composition.
(7) How much of the observed variability in published number size distributions (de Leeuw et al., 2011) is related
to analytical variability versus temporal and spatial variability in the source seawater?
(8) What is the equilibration time of surface-active marine DOM with rising bubbles in seawater, and how does this
relate to average bubble penetration depths in seawater and in bubble-based aerosol generators?
(9) What is the experimental approach that should be used to study the photochemistry of marine aerosol? This is
difficult to accomplish, but necessary to understand the aging and atmospheric impact of marine aerosol.
The general consensus of the aerosol discussion session was that we need to move forward on many fronts with
both lab-based and field-oriented studies. A systems approach will be needed that involves the international
community with many lab groups employing different techniques working on same sample sets to address these
questions.