AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Ice Nuclei Production from Sea Spray
PAUL DEMOTT, Ryan Sullivan, Kimberly Prather, Thomas C. Hill, Gary D. Franc, Allan Bertram, Ryan Mason, Timothy Guasco, Douglas Collins, Luis Cuadra-Rodriguez, Andrew Ault, Vicki Grassian, Colorado State University
Abstract Number: 612 Working Group: Aerosols, Clouds, and Climate
Abstract The sources, abundance, nature of atmospheric particles that serve as ice nuclei (IN) are not well characterized, leading to uncertain impacts on clouds, precipitation and climate. Oceanic IN sources are less well defined than known terrestrial sources, yet their potential importance is large due to the occurrence of cold cloud systems over vast oceanic regions of the Northern and Southern Hemisphere (SH). Past research suggests modest oceanic sources of IN to the atmosphere on average, but with strong heterogeneity and episodic IN production associated with marine biological processes.
In this study, we present measurements on aerosols produced from sea spray, isolated from actual seawater via breaking wave action in a laboratory wave channel facility. The temperature spectrum of freezing nuclei was determined from -10 to -35C using multiple methods. Small fractions of the generated particles were active as IN, decreasing roughly an order of magnitude per 5 degree increase in temperature, with a characteristic value of 3 per liter of air at -30C. Lower numbers of IN active at modest supercooling is consistent with past measurements over SH oceans, and appears consistent with reports of more persistent supercooled clouds at SH higher latitudes, and the difficulty that global climate models have in reproducing the energy balance related to clouds in this region.
The composition of IN produced from sea spray is still under investigation. Collected IN residuals examined by SEM were conspicuous in the absence of recognizable bacterial cells, but included certain types of sea salt particles with inclusions, as well as unidentified submicron particles containing elements of Ca, Mg, P, S, and C. Lowest IN concentrations were measured during periods of high organic aerosol loading, measured by single particle mass spectrometry, following additions of bacteria and nutrients to sea water. IN concentrations recovered as cells fed on these nutrients.