5 research outputs found
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
On the Role of Particle Inorganic Mixing State in the Reactive Uptake of N<sub>2</sub>O<sub>5</sub> to Ambient Aerosol Particles
The
rates of heterogeneous reactions of trace gases with aerosol
particles are complex functions of particle chemical composition,
morphology, and phase state. Currently, the majority of model parametrizations
of heterogeneous reaction kinetics focus on the population average
of aerosol particle mass, assuming that individual particles have
the same chemical composition as the average state. Here we assess
the impact of particle mixing state on heterogeneous reaction kinetics
using the N<sub>2</sub>O<sub>5</sub> reactive uptake coefficient,
γÂ(N<sub>2</sub>O<sub>5</sub>), and dependence on the particulate
chloride-to-nitrate ratio (<i>n</i>Cl<sup>–</sup>/<i>n</i>NO<sub>3</sub><sup>–</sup>). We describe
the first simultaneous ambient observations of single particle chemical
composition and in situ determinations of γÂ(N<sub>2</sub>O<sub>5</sub>). When accounting for particulate <i>n</i>Cl<sup>–</sup>/<i>n</i>NO<sub>3</sub><sup>–</sup> mixing state, model parametrizations of γÂ(N<sub>2</sub>O<sub>5</sub>) continue to overpredict γÂ(N<sub>2</sub>O<sub>5</sub>) by more than a factor of 2 in polluted coastal regions, suggesting
that chemical composition and physical phase state of particulate
organics likely control γÂ(N<sub>2</sub>O<sub>5</sub>) in these
air masses. In contrast, direct measurement of γÂ(N<sub>2</sub>O<sub>5</sub>) in air masses of marine origin are well captured by
model parametrizations and reveal limited suppression of γÂ(N<sub>2</sub>O<sub>5</sub>), indicating that the organic mass fraction
of fresh sea spray aerosol at this location does not suppress γÂ(N<sub>2</sub>O<sub>5</sub>). We provide an observation-based framework
for assessing the impact of particle mixing state on gas–particle
interactions
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
Transition Metal Associations with Primary Biological Particles in Sea Spray Aerosol Generated in a Wave Channel
In
the ocean, breaking waves generate air bubbles which burst at
the surface and eject sea spray aerosol (SSA), consisting of sea salt,
biogenic organic species, and primary biological aerosol particles
(PBAP). Our overall understanding of atmospheric biological particles
of marine origin remains poor. Here, we perform a control experiment,
using an aerosol time-of-flight mass spectrometer to measure the mass
spectral signatures of individual particles generated by bubbling
a salt solution before and after addition of heterotrophic marine
bacteria. Upon addition of bacteria, an immediate increase occurs
in the fraction of individual particle mass spectra containing magnesium,
organic nitrogen, and phosphate marker ions. These biological signatures
are consistent with 21% of the supermicrometer SSA particles generated
in a previous study using breaking waves in an ocean-atmosphere wave
channel. Interestingly, the wave flume mass spectral signatures also
contain metal ions including silver, iron, and chromium. The nascent
SSA bioparticles produced in the wave channel are hypothesized to
be as follows: (1) whole or fragmented bacterial cells which bioaccumulated
metals and/or (2) bacteria-derived colloids or biofilms which adhered
to the metals. This study highlights the potential for transition
metals, in combination with specific biomarkers, to serve as unique
indicators for the presence of marine PBAP, especially in metal-impacted
coastal regions