5 research outputs found
Effect of Structural Heterogeneity in Chemical Composition on Online Single-Particle Mass Spectrometry Analysis of Sea Spray Aerosol Particles
Knowledge of the surface composition
of sea spray aerosols (SSA)
is critical for understanding and predicting climate-relevant impacts.
Offline microscopy and spectroscopy studies have shown that dry supermicron
SSA tend to be spatially heterogeneous particles with sodium- and
chloride-rich cores surrounded by organic enriched surface layers
containing minor inorganic seawater components such as magnesium and
calcium. At the same time, single-particle mass spectrometry reveals
several different mass spectral ion patterns, suggesting that there
may be a number of chemically distinct particle types. This study
investigates factors controlling single particle mass spectra of nascent
supermicron SSA. Depth profiling experiments conducted on SSA generated
by a fritted bubbler and total ion intensity analysis of SSA generated
by a marine aerosol reference tank were compared with observations
of ambient SSA observed at two coastal locations. Analysis of SSA
produced by utilizing controlled laboratory methods reveals that single-particle
mass spectra with weak sodium ion signals can be produced by the desorption
of the surface of typical dry SSA particles composed of salt cores
and organic-rich coatings. Thus, this lab-based study for the first
time unifies findings from offline and online measurements as well
as lab and field studies of the SSA particle-mixing state
Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments
Cigarette
smoke is an important source of particles and gases in
the indoor environment. In this work, aging of side-stream cigarette
smoke was studied in an environmental chamber via exposure to ozone
(O<sub>3</sub>), hydroxyl radicals (OH) and indoor fluorescent lights.
Aerosol mass concentrations increased by 13–18% upon exposure
to 15 ppb O<sub>3</sub> and by 8–42% upon exposure to 0.45
ppt OH. Ultrafine particle (UFP) formation was observed during all
ozone experiments, regardless of the primary smoke aerosol concentration
(185–1950 μg m<sup>–3</sup>). During OH oxidation,
however, UFP formed only when the primary particle concentration was
relatively low (<130 μg m<sup>–3</sup>) and the OH
concentration was high (∼1.1 × 10<sup>7</sup> molecules
cm<sup>–3</sup>). Online aerosol composition measurements show
that oxygen- and nitrogen- containing species were formed during oxidation.
Gas phase oxidation of NO to NO<sub>2</sub> occurred during fluorescent
light exposure, but neither primary particle growth nor UFP formation
were observed. Overall, exposure of cigarette smoke to ozone will
likely lead to UFP formation in indoor environments. On the other
hand, UPF formation via OH oxidation will only occur when OH concentrations
are high (∼10<sup>7</sup> molecules cm<sup>–3</sup>),
and is therefore less likely to have an impact on indoor aerosol associated
with cigarette smoke
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