Light-enhanced primary marine aerosol production from biologically productive seawater

Breaking waves on the ocean surface produce bubbles that burst at the air-sea interface and inject sea spray aerosol (SSA) into the atmosphere ranging in size from 0.01 to 20 micrometers. This process is the dominant source of aerosol particle mass and a major source of aerosol particle number to the Earth's atmosphere. The resulting SSA has significant impacts on atmospheric chemistry and physics. SSA production and properties are influenced by organic matter in seawater that adsorbs to the surfaces of freshly produced bubbles, forming organic films on the emitted SSA. Although research spanning several decades has studied various aspects of SSA production, it is still not well understood how surface ocean biogeochemistry and seawater organic matter affect SSA production and composition.

In May of 2010 and August of 2012, PMEL-led research cruises were conducted in the NE Pacific and NW Atlantic oceans, respectively, with the goal of generating freshly emitted SSA to estimate emission fluxes and assess the role of local biological activity on SSA properties. This recently published article in Geophysical Research Letters, co-authored by NOAA PMEL and JISAO scientists, Trish Quinn and Tim Bates, reports on results from those two cruises, which indicate that surface ocean biogeochemistry plays a role in the physical mechanism of sea spray aerosol production.

Long et al. (2011) generated SSA from seawater using a chamber that mimics conditions of the surface ocean. While stationed in a region of biologically productive waters in the North Atlantic, the emission flux of SSA mass and number was found to increase rapidly at sunrise and then decrease overnight. This diel variability was not observed when the ship was stationed in the biologically non-productive waters of the Sargasso Sea. The observed diel variability in SSA production for biologically productive regions provides direct evidence for a sunlight-mediated process that results in the formation of surfactant organic matter in the surface ocean that modulates the physics of SSA production.

Long et al. (2011) also measured seawater bubble surface tension and found that surfactants were present on bubble surfaces in regions of both high and low biological activity. It was concluded that at least two distinct reservoirs of surface-active organic surfactants are present in biologically productive waters, one of which is controlled by solar radiation in the surface ocean. The effect of solar radiation on the production of surfactant organic matter, possibly through a biological process that is coupled to or independent of photochemical transformations of organic matter, diurnally modulates the production of SSA from productive but not non-productive waters. Although the total emission of SSA differs between regions of high and low biological activity, the fraction of SSA that is organic does not suggesting it is a change in the composition of the organic matter that affects the physical production mechanism.