Sea Spray Aerosol: Where Marine Biology Meets Atmospheric Chemistry

Abstract

Atmospheric aerosols have long been known to alter climate by scattering incoming solar radiation and acting as seeds for cloud formation. These processes have vast implications for controlling the chemistry of our environment and the Earth's climate. Sea spray aerosol (SSA) is emitted over nearly three-quarters of our planet, yet precisely how SSA impacts Earth's radiation budget remains highly uncertain. Over the past several decades, studies have shown that SSA particles are far more complex than just sea salt. Ocean biological and physical processes produce individual SSA particles containing a diverse array of biological species including proteins, enzymes, bacteria, and viruses and a diverse array of organic compounds including fatty acids and sugars. Thus, a new frontier of research is emerging at the nexus of chemistry, biology, and atmospheric science. In this Outlook article, we discuss how current and future aerosol chemistry research demands a tight coupling between experimental (observational and laboratory studies) and computational (simulation-based) methods. This integration of approaches will enable the systematic interrogation of the complexity within individual SSA particles at a level that will enable prediction of the physicochemical properties of real-world SSA, ultimately illuminating the detailed mechanisms of how the constituents within individual SSA impact climate.

Figure 1

Hygroscopicity and ice nucleation of pure sea salt aerosols differs from that of sea spray aerosols, which affects how these aerosols seed clouds. To study the full complexity of nascent sea spray aerosols requires the bringing the ocean into the laboratory with the application of, for example, Marine Aerosol Reference Tanks (MARTs).

Figure 2

(Left column, top to bottom) The characteristics of a cell including the presence and structure of the outer membrane, presence of interior membranes, presence of bacterial derivatives, and the impacts of pH and salt on cellular chemistry. (Right column) The analogous traits found within sea spray aerosols.

Figure 3

Examples of some methods to study substrate-deposited particles for (a) water uptake and hygroscopic growth (see ref (48) for more details) and (b) ice nucleation of individual sea spray aerosol particles. The importance of these techniques is that they provide measurements of atmospheric processes (hygroscopicity, IN activity, etc.) with added chemical information from vibrational spectroscopy.

Figure 4

Futuristic workflow for connecting atomic-level mechanisms with environmentally relevant properties of SSA. Results from hygroscopic growth experiments (1) can be coupled with (2) AFM-IR (or micro-Raman) measurements to understand single particle CCN and IN chemical characteristics, over the growth of a phytoplankton bloom. Single particle surface tension with AFM (or other methods to measure surface tension) can then be linked with (3) high resolution mass spectrometry to (4) construct molecular networks with GNPS and finally (5) use these molecular networks to construct atomic level molecular dynamics simulations of full aerosol particles.