Size-Dependent Changes in Sea Spray Aerosol Composition
and Properties with Different Seawater Conditions
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Abstract
A great deal of uncertainty exists
regarding the chemical diversity
of particles in sea spray aerosol (SSA), as well as the degree of
mixing between inorganic and organic species in individual SSA particles.
Therefore, in this study, single particle analysis was performed on
SSA particles, integrating transmission electron microscopy with energy
dispersive X-ray analysis and scanning transmission X-ray microscopy
with near edge X-ray absorption fine structure spectroscopy, with
a focus on quantifying the relative fractions of different particle
types from 30 nm to 1 μm. SSA particles were produced from seawater
in a unique ocean-atmosphere facility equipped with breaking waves.
Changes to the SSA composition and properties after the addition of
biological (bacteria and phytoplankton) and organic material (ZoBell
growth media) were probed. Submicrometer SSA particles could be separated
into two distinct populations: one with a characteristic sea salt
core composed primarily of NaCl and an organic carbon and Mg<sup>2+</sup> coating (SS-OC), and a second type consisting of organic carbon
(OC) species which are more homogeneously mixed with cations and anions,
but not chloride. SS-OC particles exhibit a wide range of sizes, compositions,
morphologies, and distributions of elements within each particle.
After addition of biological and organic material to the seawater,
a change occurs in particle morphology and crystallization behavior
associated with increasing organic content for SS-OC particles. The
fraction of OC-type particles, which are mainly present below 180
nm, becomes dramatically enhanced with increased biological activity.
These changes with size and seawater composition have important implications
for atmospheric processes such as cloud droplet activation and heterogeneous
reactivity