14 research outputs found
Expanding Single Particle Mass Spectrometer Analyses for the Identification of Microbe Signatures in Sea Spray Aerosol
Ocean-derived microbes
in sea spray aersosol (SSA) have the potential
to influence climate and weather by acting as ice nucleating particles
in clouds. Single particle mass spectrometers (SPMSs), which generate <i>in situ</i> single particle composition data, are excellent
tools for characterizing aerosols under changing environmental conditions
as they can provide high temporal resolution and require no sample
preparation. While SPMSs have proven capable of detecting microbes,
these instruments have never been utilized to definitively identify
aerosolized microbes in ambient sea spray aersosol. In this study,
an aerosol time-of-flight mass spectrometer was used to analyze laboratory
generated SSA produced from natural seawater in a marine aerosol reference
tank. We present the first description of a population of biological
SSA mass spectra (BioSS), which closely match the ion signatures observed
in previous terrestrial microbe studies. The fraction of BioSS dramatically
increased in the largest supermicron particles, consistent with field
and laboratory measurements of microbes ejected by bubble bursting,
further supporting the assignment of BioSS mass spectra as microbes.
Finally, as supported by analysis of inorganic ion signals, we propose
that dry BioSS particles have heterogeneous structures, with microbes
adhered to sodium chloride nodules surrounded by magnesium-enriched
coatings. Consistent with this structure, chlorine-containing ion
markers were ubiquitous in BioSS spectra and identified as possible
tracers for distinguishing recently aerosolized marine from terrestrial
microbes
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
Impacts of Aerosol Aging on Laser Desorption/Ionization in Single-Particle Mass Spectrometers
<div><p>Single-particle mass spectrometry (SPMS) has been widely used for characterizing the chemical mixing state of ambient aerosol particles. However, processes occurring during particle ablation and ionization can influence the mass spectra produced by these instruments. These effects remain poorly characterized for complex atmospheric particles. During the 2005 Study of Organic Aerosols in Riverside (SOAR), a thermodenuder was used to evaporate the more volatile aerosol species in sequential temperature steps up to 230°C; the residual aerosol particles were sampled by an aerosol mass spectrometer (AMS) and a single-particle aerosol time-of-flight mass spectrometer (ATOFMS). Removal of the secondary species (e.g., ammonium nitrate/sulfate) through heating permitted assessment of the change in ionization patterns as the composition changed for a given particle type. It was observed that a coating of secondary species can reduce the ionization efficiency by changing the degree of laser absorption or particle ablation, which significantly impacted the measured ion peak areas. Nonvolatile aerosol components were used as pseudo-internal standards (or âreference componentsâ) to correct for this LDI effect. Such corrected ATOFMS ion peak areas correlated well with the AMS measurements of the same species up to 142°C. This work demonstrates the potential to accurately relate SPMS peak areas to the mass of specific aerosol components.</p><p>Copyright 2014 American Association for Aerosol Research</p></div
Air Quality Impact and Physicochemical Aging of Biomass Burning Aerosols during the 2007 San Diego Wildfires
Intense wildfires burning >360â000
acres in San Diego during
October, 2007 provided a unique opportunity to study the impact of
wildfires on local air quality and biomass burning aerosol (BBA) aging.
The size-resolved mixing state of individual particles was measured
in real-time with an aerosol time-of-flight mass spectrometer (ATOFMS)
for 10 days after the fires commenced. Particle concentrations were
high county-wide due to the wildfires; 84% of 120â400 nm particles
by number were identified as BBA, with particles <400 nm contributing
to mass concentrations dangerous to public health, up to 148 ÎŒg/m<sup>3</sup>. Evidence of potassium salts heterogeneously reacting with
inorganic acids was observed with continuous high temporal resolution
for the first time. Ten distinct chemical types shown as BBA factors
were identified through positive matrix factorization coupled to single
particle analysis, including particles comprised of potassium chloride
and organic nitrogen during the beginning of the wildfires, ammonium
nitrate and amines after an increase of relative humidity, and sulfate
dominated when the air mass back trajectories passed through the Los
Angeles port region. Understanding BBA aging processes and quantifying
the size-resolved mass and number concentrations are important in
determining the overall impact of wildfires on air quality, health,
and climate
Heterogeneous Chemistry of Lipopolysaccharides with Gas-Phase Nitric Acid: Reactive Sites and Reaction Pathways
Recent
studies have shown that sea spray aerosol (SSA) has a size-dependent,
complex composition consisting of biomolecules and biologically derived
organic compounds in addition to salts. This additional chemical complexity
most likely influences the heterogeneous reactivity of SSA, as these
other components will have different reactive sites and reaction pathways.
In this study, we focus on the reactivity of a class of particles
derived from some of the biological components of sea spray aerosol
including lipopolysaccharides (LPS) that undergo heterogeneous chemistry
within the reactive sites of the biological molecule. Examples of
these reactions and the relevant reactive sites are proposed as follows:
RâCOONa<sub>(s)</sub> + HNO<sub>3(g)</sub> â NaNO<sub>3</sub> + RâCOOH and RâHPO<sub>4</sub>Na<sub>(s)</sub> + HNO<sub>3(g)</sub> â NaNO<sub>3</sub> + RâH<sub>2</sub>PO<sub>4</sub>. These reactions may be a heterogeneous pathway
not only for sea spray aerosol but also for a variety of other types
of atmospheric aerosol as well
Laboratory Studies of the Cloud Droplet Activation Properties and Corresponding Chemistry of Saline Playa Dust
Playas
emit large quantities of dust that can facilitate the activation
of cloud droplets. Despite the potential importance of playa dusts
for cloud formation, most climate models assume that all dust is nonhygroscopic;
however, measurements are needed to clarify the role of dusts in aerosol-cloud
interactions. Here, we report measurements of CCN activation from
playa dusts and parameterize these results in terms of both Îș-KoÌhler
theory and adsorption activation theory for inclusion in atmospheric
models. Îș ranged from 0.002 ± 0.001 to 0.818 ± 0.094,
whereas Frankel-Halsey-Hill (FHH) adsorption parameters of <i>A</i><sub>FHH</sub> = 2.20 ± 0.60 and <i>B</i><sub>FHH</sub> = 1.24 ± 0.14 described the water uptake properties
of the dusts. Measurements made using aerosol time-of-flight mass
spectrometry (ATOFMS) revealed the presence of halite, sodium sulfates,
and sodium carbonates that were strongly correlated with Îș underscoring
the role that mineralogy, including salts, plays in water uptake by
dust. Predictions of Îș made using bulk chemical techniques generally
showed good agreement with measured values. However, several samples
were poorly predicted suggesting that chemical heterogeneities as
a function of size or chemically distinct particle surfaces can determine
the hygroscopicity of playa dusts. Our results further demonstrate
the importance of dust in aerosolâcloud interactions
Direct Night-Time Ejection of Particle-Phase Reduced Biogenic Sulfur Compounds from the Ocean to the Atmosphere
The
influence of oceanic biological activity on sea spray aerosol
composition, clouds, and climate remains poorly understood. The emission
of organic material and gaseous dimethyl sulfide (DMS) from the ocean
represents well-documented biogenic processes that influence particle
chemistry in marine environments. However, the direct emission of
particle-phase biogenic sulfur from the ocean remains largely unexplored.
Here we present measurements of ocean-derived particles containing
reduced sulfur, detected as elemental sulfur ions (e.g., <sup>32</sup>S<sup>+</sup>, <sup>64</sup>S<sub>2</sub><sup>+</sup>), in seven
different marine environments using <i>real-time</i>, single
particle mass spectrometry; these particles have not been detected
outside of the marine environment. These reduced sulfur compounds
were associated with primary marine particle types and wind speeds
typically between 5 and 10 m/s suggesting that these particles themselves
are a primary emission. In studies with measurements of seawater properties,
chlorophyll-<i>a</i> and atmospheric DMS concentrations
were typically elevated in these same locations suggesting a biogenic
source for these sulfur-containing particles. Interestingly, these
sulfur-containing particles only appeared at night, likely due to
rapid photochemical destruction during the daytime, and comprised
up to âŒ67% of the aerosol number fraction, particularly in
the supermicrometer size range. These sulfur-containing particles
were detected along the California coast, across the Pacific Ocean,
and in the southern Indian Ocean suggesting that these particles represent
a globally significant biogenic contribution to the marine aerosol
burden
Online Analysis of Single Cyanobacteria and Algae Cells under Nitrogen-Limited Conditions Using Aerosol Time-of-Flight Mass Spectrometry
Metabolomics studies typically perform
measurements on populations
of whole cells which provide the average representation of a collection
of many cells. However, key mechanistic information can be lost using
this approach. Investigating chemistry at the single cell level yields
a more accurate representation of the diversity of populations within
a cell sample; however, this approach has many analytical challenges.
In this study, an aerosol time-of-flight mass spectrometer (ATOFMS)
was used for rapid analysis of single algae and cyanobacteria cells
with diameters ranging from 1 to 8 ÎŒm. Cells were aerosolized
by nebulization and directly transmitted into the ATOFMS. Whole cells
were determined to remain intact inside the instrument through a combination
of particle sizing and imaging measurements. Differences in cell populations
were observed after perturbing <i>Chlamydomonas reinhardtii</i> cells via nitrogen deprivation. Thousands of single cells were measured
over a period of 4 days for nitrogen-replete and nitrogen-limited
conditions. A comparison of the single cell mass spectra of the cells
sampled under the two conditions revealed an increase in the dipalmitic
acid sulfolipid sulfoquinovosyldiacylglycerol (SQDG), a chloroplast
membrane lipid, under nitrogen-limited conditions. Single cell peak
intensity distributions demonstrate the ability of the ATOFMS to measure
metabolic differences of single cells. The ATOFMS provides an unprecedented
maximum throughput of 50 Hz, enabling the rapid online measurement
of thousands of single cell mass spectra
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