Harmful algal blooms (HABs) can generate toxins that can be aerosolized and negatively impact human health through inhalation. HABs are often found in waterways near residences, therefore, ...aerosolized HAB toxins can potentially affect both indoor and outdoor air quality. Given that HABs are predicted to increase worldwide, effective mitigation strategies are needed to prevent the inhalation of aerosolized HAB toxins. In this work, we characterized both the particle filtration efficiency using particle sizing instruments as well as the mass concentration of different congeners of aerosolized microcystin (MC) toxins that penetrate through commercially available face masks and air conditioner (AC) filters. Particles were generated from cultures of the toxin-producing cyanobacteria Microcystis aeruginosa. Hydrophobic congeners of microcystin including MC-LF and MC-LW were enriched in aerosols compared to water, with MC-LR being the most abundant, which has implications for the toxicity of inhalable particles generated from HAB-contaminated waters. Particle transmission efficiencies and toxin filtration efficiencies scaled with the manufacturer-provided filter performance ratings. Up to 80% of small, microcystin-containing aerosols were transmitted through AC filters with low filter performance ratings. In contrast, both face masks as well as AC filters with high filter performance ratings efficiently removed toxin-containing particles to below limits of quantification. Our findings suggest that face masks and commercially available AC filters with high filtration efficiency ratings are suitable mitigation strategies to avoid indoor and outdoor air exposure to aerosolized HAB toxins. This work also has relevance for reducing airborne exposure to other HAB toxins, non-HAB toxins, pathogens, and viruses, including SARS-CoV-2, the virus responsible for the COVID-19 pandemic.
One of the challenges of understanding atmospheric organic aerosol (OA)
particles stems from its complex composition. Mass spectrometry is commonly
used to characterize the compositional variability ...of OA. Clustering of a
mass spectral dataset helps identify components that exhibit similar
behavior or have similar properties, facilitating understanding of sources
and processes that govern compositional variability. Here, we developed an
algorithm for clustering mass spectra, the noise-sorted scanning clustering
(NSSC), appropriate for application to thermal desorption measurements of
collected OA particles from the Filter Inlet for Gases and AEROsols coupled
to a chemical ionization mass spectrometer (FIGAERO-CIMS). NSSC, which
extends the common density-based special clustering of applications with noise (DBSCAN) algorithm, provides a robust, reproducible
analysis of the FIGAERO temperature-dependent mass spectral data. The NSSC
allows for the determination of thermal profiles for compositionally distinct
clusters of mass spectra, increasing the accessibility and enhancing the
interpretation of FIGAERO data. Applications of NSSC to several laboratory
biogenic secondary organic aerosol (BSOA) systems demonstrate the ability of
NSSC to distinguish different types of thermal behaviors for the components
comprising the particles along with the relative mass contributions and
chemical properties (e.g., average molecular formula) of each mass spectral
cluster. For each of the systems examined, more than 80 % of the total
mass is clustered into 9–13 mass spectral clusters. Comparison of the
average thermograms of the mass spectral clusters between systems indicates
some commonality in terms of the thermal properties of different BSOA,
although with some system-specific behavior. Application of NSSC to sets of
experiments in which one experimental parameter, such as the concentration
of NO, is varied demonstrates the potential for mass spectral clustering to
elucidate the chemical factors that drive changes in the thermal properties
of OA particles. Further quantitative interpretation of the thermograms of
the mass spectral clusters will allow for a more comprehensive understanding
of the thermochemical properties of OA particles.
During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert, reaching the Caribbean Basin, Gulf Coast, and southeastern ...United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021 generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve nutrient limitation of phosphorus (P) in the P-stressed North Atlantic, less is known about the impact of extreme events and other natural aerosols on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P and iron (Fe) content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point, Barbados. We also performed seawater incubations to assess the marine microbial response to aerosol deposition. Using environmentally-relevant concentrations of atmospheric particles for within the ocean’s mixed layer allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content than mineral dust, and P in volcanic ash is far less soluble (~1%) than assumed in current atmospheric deposition models. Adding mineral dust and the volcanic ash leachate in concentrations representing different deposition scenarios increased soluble reactive phosphorus (SRP) concentrations in coastal seawater by ~7-32 nM. Phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event, with ash eliciting the fastest uptake rate. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump.
Atomic chlorine (Cl
) affects air quality and atmospheric oxidizing capacity. Nitryl chloride (ClNO
) - a common Cl
source-forms when chloride-containing aerosols react with dinitrogen pentoxide (N
O
...). A recent study showed that saline lakebed (playa) dust is an inland source of particulate chloride (Cl
) that generates high ClNO
. However, the underlying physiochemical factors responsible for observed yields are poorly understood. To elucidate these controlling factors, we utilized single particle and bulk techniques to determine the chemical composition and mineralogy of playa sediment and dust samples from the southwest United States. Single particle analysis shows trace highly hygroscopic magnesium and calcium Cl-containing minerals are present and likely facilitate ClNO
formation at low humidity. Single particle and mineralogical analysis detected playa sediment organic matter that hinders N
O
uptake as well as 10 Å-clay minerals (e.g., Illite) that compete with water and chloride for N
O
. Finally, we show that the composition of the aerosol surface, rather than the bulk, is critical in ClNO
formation. These findings underscore the importance of mixing state, competing reactions, and surface chemistry on N
O
uptake and ClNO
yield for playa dusts and, likely, other aerosol systems. Therefore, consideration of particle surface composition is necessary to improve ClNO
and air quality modeling.
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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 N2O5 reactive uptake coefficient, γ(N2O5), and dependence on the particulate chloride-to-nitrate ratio (nCl–/nNO3 –). We describe the first simultaneous ambient observations of single particle chemical composition and in situ determinations of γ(N2O5). When accounting for particulate nCl–/nNO3 – mixing state, model parametrizations of γ(N2O5) continue to overpredict γ(N2O5) by more than a factor of 2 in polluted coastal regions, suggesting that chemical composition and physical phase state of particulate organics likely control γ(N2O5) in these air masses. In contrast, direct measurement of γ(N2O5) in air masses of marine origin are well captured by model parametrizations and reveal limited suppression of γ(N2O5), indicating that the organic mass fraction of fresh sea spray aerosol at this location does not suppress γ(N2O5). We provide an observation-based framework for assessing the impact of particle mixing state on gas–particle interactions.
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Marine aerosols are a globally significant contributor to aerosol-cloud-climate interactions; however, the impact that different sources of pollution and natural emissions from the ocean have on the ...water uptake properties of marine aerosols remains largely underexplored. Here we present measurements of the cloud condensation nuclei (CCN) activation of marine aerosols taken in a coastal, marine environment impacted by sea spray aerosol and different sources of pollution. The hygroscopicity parameter, κ, was found to range from <0.1 up to 1.4 with a campaign-average value of 0.22 ± 0.12. Smaller particles were less hygroscopic than larger ones, and κ varied diurnally and temporally as a function of air mass transport conditions. Measurements made using aerosol time-of-flight mass spectrometry (ATOFMS) revealed that heterogeneous reactions, sulfates, and temporal differences in the observed particle types had the largest impacts on the observed κ values. The aerosol mixing-state was also found to affect κ. Temporal differences between freshly-emitted soot and aged soot internally mixed with sulfates, likely emitted from ships, had the largest impact on diurnal variations in κ. Our results further demonstrate the significant impact that pollution and the aerosol mixing-state have on aerosol-cloud interactions in the marine boundary layer.
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., 32S+, 64S2 +), in seven different marine environments using real-time, 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-a 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 ∼67% 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.
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During the Ice in Clouds Experiment‐Layer Clouds (ICE‐L), dry lakebed, or playa, salts from the Great Basin region of the United States were observed as cloud nuclei in orographic wave clouds over ...Wyoming. Using a counterflow virtual impactor in series with a single‐particle mass spectrometer, sodium‐potassium‐magnesium‐calcium‐chloride salts were identified as residues of cloud droplets. Importantly, these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei (CCN) efficiencies close to sea salt. Using a suite of chemical characterization instrumentation, the playa salts were observed to be internally mixed with oxidized organics, presumably produced by cloud processing, as well as carbonate. These salt particles were enriched as residues of large droplets (>19 μm) compared to smaller droplets (>7 μm). In addition, a small fraction of silicate‐containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes. While the high CCN activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments, this study provides direct evidence of the importance of playa salts in cloud formation in continental North America has not been shown previously. Studies are needed to model and quantify the impact of playas on climate globally, particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes.
Oceans represent a significant natural source of gases and particles to the atmosphere. Relative to gas phase compounds, less is known regarding the influence of changes in biological activity in the ...ocean on the chemistry of sea spray aerosols produced in marine environments. To gain insight into the influence of ocean biology and chemistry on atmospheric aerosol chemistry, simultaneous real‐time measurements were made of atmospheric aerosol size and chemical mixing‐state, gas phase dimethyl sulfide (DMS), as well as seawater DMS and chlorophyll a. In three different marine environments with elevated chlorophyll a and DMS, unique Mg particles were detected containing Mg2+, Ca2+, K+, and organic carbon. These particles were segregated from sea salt particles highlighting that two subpopulations within the sea spray were being ejected from the ocean. Strong temporal correlations were observed between these unique ocean‐derived particles and freshly emitted sea salt particles (R2 = 0.86), particularly as wind speed increased to at least 10 m/s, and atmospheric DMS (R2 = 0.76). Time series correlations between ocean measurements and atmospheric aerosol chemistry suggest that chlorophyll a and DMS serve as indicators of changes in the chemistry of the ocean, most likely an increase in organic material, which is directly reflected in the single particle mixing‐state. This is the first time such real‐time correlations are shown between ocean chemistry and atmospheric aerosol mixing‐state. The reasons behind these observed changes in aerosol chemistry are critical for understanding the heterogeneous reactivity, water uptake, and cloud forming potential of sea spray aerosols.
Key Points
Enrichment of alkaline metals is occurring in sea spray aerosol
This chemical enrichment is occurring at the single particle level
These unique particles are correlated with other tracers of biological activity
A combination of flow reactor studies and chamber modeling is used to constrain two uncertain parameters central to the formation of secondary organic aerosol (SOA) from isoprene-derived epoxides: ...(1) the rate of heterogeneous uptake of epoxide to the particle phase and (2) the molar fraction of epoxide reactively taken up that contributes to SOA, the SOA yield (ϕSOA). Flow reactor measurements of the trans-β-isoprene epoxydiol (trans-β-IEPOX) and methacrylic acid epoxide (MAE) aerosol reaction probability (γ) were performed on atomized aerosols with compositions similar to those used in chamber studies. Observed γ ranges for trans-β-IEPOX and MAE were 6.5 × 10–4−0.021 and 4.9–5.2 × 10–4, respectively. Through the use of a time-dependent chemical box model initialized with chamber conditions and γ measurements, ϕSOA values for trans-β-IEPOX and MAE on different aerosol compositions were estimated between 0.03–0.21 and 0.07–0.25, respectively, with the MAE ϕSOA showing more uncertainty.
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