4 research outputs found
Size-Resolved Sea Spray Aerosol Particles Studied by Vibrational Sum Frequency Generation
We present vibrational sum frequency
generation (SFG) spectra of
the external surfaces and the internal interfaces of size-selected
sea spray aerosol (SSA) particles generated at the wave flume of the
Scripps Hydraulics Laboratory. Our findings support SSA particle models
that invoke the presence of surfactants in the topmost particle layer
and indicate that the alkyl chains of surfactant-rich SSA particles
are likely to be disordered. Specifically, the SFG spectra suggest
that across the range of sizes studied, surfactant-rich SSA particles
contain CH oscillators that are subject to molecular orientation distributions
that are broader than the narrow molecular distribution functions
associated with well-ordered and well-aligned alkyl chains. This result
is consistent with the interpretation that the permeability of organic
layers at SSA particle surfaces to small reactive and nonreactive
molecules may be substantial, allowing for much more exchange between
reactive and nonreactive species in the gas or the condensed phase
than previously thought. The SFG data also suggest that a one-component
model is likely to be insufficient for describing the SFG responses
of the SSA particles. Finally, the similarity of the SFG spectra obtained
from the wave flume microlayer and 150 nm-sized SSA particles suggests
that the SFG active CH oscillators in the topmost layer of the wave
flume and the particle accumulation mode may be in similar chemical
environments. Needs for additional research activities are discussed
in the context of the results presented
Inside versus Outside: Ion Redistribution in Nitric Acid Reacted Sea Spray Aerosol Particles as Determined by Single Particle Analysis
Single particle analysis of individual
sea spray aerosol particles
shows that cations (Na<sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>, and Ca<sup>2+</sup>) within individual particles undergo a spatial
redistribution after heterogeneous reaction with nitric acid, along
with the development of a more concentrated layer of organic matter
at the surface of the particle. These data suggest that specific ion
and aerosol pH effects play an important role in aerosol particle
structure in ways that have not been previously recognized
Heterogeneous Reactivity of Nitric Acid with Nascent Sea Spray Aerosol: Large Differences Observed between and within Individual Particles
Current
climate and atmospheric chemistry models assume that all
sea spray particles react as if they are pure NaCl. However, recent
studies of sea spray aerosol particles have shown that distinct particle
types exist (including sea salt, organic carbon, and biological particles)
as well as mixtures of these and, within each particle type, there
is a range of single-particle chemical compositions. Because of these
differences, individual particles should display a range of reactivities
with trace atmospheric gases. Herein, to address this, we study the
composition of individual sea spray aerosol particles after heterogeneous
reaction with nitric acid. As expected, a replacement reaction of
chloride with nitrate is observed; however, there is a large range
of reactivities spanning from no reaction to complete reaction between
and within individual sea spray aerosol particles. These data clearly
support the need for laboratory studies of individual, environmentally
relevant particles to improve our fundamental understanding as to
the properties that determine reactivity
Size-Dependent Changes in Sea Spray Aerosol Composition and Properties with Different Seawater Conditions
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