Atmospheric Benzothiazoles in a Coastal Marine Environment.

Organic emissions from coastal waters play an important but poorly understood role in atmospheric chemistry in coastal regions. A mesocosm experiment focusing on facilitated biological blooms in coastal seawater, SeaSCAPE (Sea Spray Chemistry and Particle Evolution), was performed to study emission of volatile gases, primary sea spray aerosol, and formation of secondary marine aerosol as a function of ocean biological and chemical processes. Here, we report observations of aerosol-phase benzothiazoles in a marine atmospheric context with complementary measurements of dissolved-phase benzothiazoles. Though previously reported dissolved in polluted coastal waters, we report the first direct evidence of the transfer of these molecules from seawater into the atmosphere. We also report the first gas-phase observations of benzothiazole in the environment absent a direct industrial, urban, or rubber-based source. From the identities and temporal dynamics of the dissolved and aerosol species, we conclude that the presence of benzothiazoles in the coastal water (and thereby their emissions into the atmosphere) is primarily attributable to anthropogenic sources. Oxidation experiments to explore the atmospheric fate of gas-phase benzothiazole show that it produces secondary aerosol and gas-phase SO2, making it a potential contributor to secondary marine aerosol formation in coastal regions and a participant in atmospheric sulfur chemistry.

Rapid cloud removal of dimethyl sulfide oxidation products limits SO2 and cloud condensation nuclei production in the marine atmosphere.

Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The oxidation of DMS leads to the formation and growth of cloud condensation nuclei (CCN) with consequent effects on Earth's radiation balance and climate. The quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of existing aerosol particles and clouds. In the unpolluted marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory toward sulfur dioxide (SO2) and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that the irreversible loss of HPMTF to clouds in the marine boundary layer determines the HPMTF lifetime (τHPMTF < 2 h) and terminates DMS oxidation to SO2 When accounting for HPMTF cloud loss in a global chemical transport model, we show that SO2 production from DMS is reduced by 35% globally and near-surface (0 to 3 km) SO2 concentrations over the ocean are lowered by 24%. This large, previously unconsidered loss process for volatile sulfur accelerates the timescale for the conversion of DMS to sulfate while limiting new particle formation in the marine atmosphere and changing the dynamics of aerosol growth. This loss process potentially reduces the spatial scale over which DMS emissions contribute to aerosol production and growth and weakens the link between DMS emission and marine CCN production with subsequent implications for cloud formation, radiative forcing, and climate.

Characterization of ground-based atmospheric pollution and meteorology sampling stations during the Lake Michigan Ozone Study 2017.

The Lake Michigan Ozone Study 2017 (LMOS 2017) in May and June 2017 enabled study of transport, emissions, and chemical evolution related to ozone air pollution in the Lake Michigan airshed. Two highly instrumented ground sampling sites were part of a wider sampling strategy of aircraft, shipborne, and ground-based mobile sampling. The Zion, Illinois site (on the coast of Lake Michigan, 67 km north of Chicago) was selected to sample higher NOx air parcels having undergone less photochemical processing. The Sheboygan, Wisconsin site (on the coast of Lake Michigan, 211 km north of Chicago) was selected due to its favorable location for the observation of photochemically aged plumes during ozone episodes involving southerly winds with lake breeze. The study encountered elevated ozone during three multiday periods. Daytime ozone episode concentrations at Zion were 60 ppb for ozone, 3.8 ppb for NOx, 1.2 ppb for nitric acid, and 8.2 µg m-3 for fine particulate matter. At Sheboygan daytime, ozone episode concentrations were 60 ppb for ozone, 2.6 ppb for NOx, and 3.0 ppb for NOy. To facilitate informed use of the LMOS 2017 data repository, we here present comprehensive site description, including airmass influences during high ozone periods of the campaign, overview of meteorological and pollutant measurements, analysis of continuous emission monitor data from nearby large point sources, and characterization of local source impacts from vehicle traffic, large point sources, and rail. Consistent with previous field campaigns and the conceptual model of ozone episodes in the area, trajectories from the southwest, south, and lake breeze trajectories (south or southeast) were overrepresented during pollution episodes. Local source impacts from vehicle traffic, large point sources, and rail were assessed and found to represent less than about 15% of typical concentrations measured. Implications for model-observation comparison and design of future field campaigns are discussed.Implications: The Lake Michigan Ozone Study 2017 (LMOS 2017) was conducted along the western shore of Lake Michigan, and involved two well-instrumented coastal ground sites (Zion, IL, and Sheboygan, WI). LMOS 2017 data are publicly available, and this paper provides detailed site characterization and measurement summary to enable informed use of repository data. Minor local source impacts were detected but were largely confined to nighttime conditions of less interest for ozone episode analysis and modeling. The role of these sites in the wider field campaign and their detailed description facilitates future campaign planning, informed data repository use, and model-observation comparison.

A novel box for aerosol and droplet guarding and evacuation in respiratory infection (BADGER) for COVID-19 and future outbreaks.

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has infected millions and killed more than 1.7 million people worldwide as of December 2020. Healthcare providers are at increased risk of infection when caring for patients with COVID-19. The mechanism of transmission of SARS-CoV-2 is beginning to emerge as airborne spread in addition to direct droplet and indirect contact as main routes of transmission. Here, we report on the design, construction, and testing of the BADGER (Box for Aerosol and Droplet Guarding and Evacuation in Respiratory Infection), an affordable, scalable device that contains droplets and aerosol particles, thus minimizing the risk of infection to healthcare providers. A semi-sealed environment is created inside the BADGER, which is placed over the head of the patient and maintains at least 12-air changes per hour using in-wall vacuum suction. Multiple hand-ports enable healthcare providers to perform essential tasks on a patient's airway and head. Overall, the BADGER has the potential to contain large droplets and small airborne particles as demonstrated by simulated qualitative and quantitative assessments to provide an additional layer of protection for healthcare providers treating COVID-19 and future respiratory contagions.

Diel Profile of Hydroperoxymethyl Thioformate: Evidence for Surface Deposition and Multiphase Chemistry.

Dimethyl sulfide (DMS; CH3SCH3), a biogenically produced trace gas emitted from the ocean, accounts for a large fraction of natural sulfur released to the marine atmosphere. The oxidation of DMS in the marine boundary layer (MBL), via the hydrogen abstraction pathway, yields the short-lived methylthiomethylperoxy radical (MSP; CH3SCH2OO). In the remote MBL, unimolecular isomerization of MSP outpaces bimolecular chemistry leading to the efficient formation of hydroperoxymethyl thioformate (HPMTF; HOOCH2SCHO). Here, we report the first ground observations and diurnal profiles of HPMTF mixing ratios, vertical fluxes, and deposition velocities to the ocean surface. Average daytime HPMTF mixing ratios, fluxes, and deposition velocities were recorded at 12.1 pptv, -0.11 pptv m s-1, and 0.75 cm s-1, respectively. The deposition velocity of HPMTF is comparable to other soluble gas phase compounds (e.g., HCOOH and HNO3), resulting in a deposition lifetime of 30 h under typical windspeeds (3 m s-1). A box model analysis incorporating the current mechanistic understanding of DMS oxidation chemistry and geostationary satellite cloud imagery data suggests that the lifetime of HPMTF in the MBL at this sampling location is likely controlled by heterogeneous loss to aerosol and uptake to clouds in the morning and evening.

Reactive VOC Production from Photochemical and Heterogeneous Reactions Occurring at the Air-Ocean Interface.

The ocean surface serves as a source and sink for a diverse set of reactive trace gases in the atmosphere, including volatile organic compounds (VOCs), reactive halogens, and oxidized and reduced nitrogen compounds. The exchange of reactive trace gases between the atmosphere and ocean has been shown to alter atmospheric oxidant concentrations and drive particle nucleation and growth. Uncertainties in cloud radiative forcing and aerosol-cloud interactions are among the largest uncertainties in current global climate models. Climate models are particularly sensitive to cloud cover over the remote ocean due to large changes in albedo between the ocean surface and cloud tops. Oceanic emissions contribute to cloud condensation nuclei concentrations, either through the direct emission of particles during wave breaking or through the formation of secondary aerosol particles following the emission of reactive gas-phase compounds. Despite generally small and diffuse oceanic emission rates for reactive trace gases, it has been shown that oxidant and particle number concentrations are acutely sensitive to air-sea trace gas exchange rates and the chemical composition of emitted species. To date, field measurements of air-sea reactive gas exchange have focused primarily on the emission of gases of biological origin, such as dimethyl sulfide (DMS). While DMS emissions are relatively well constrained, the gas-phase oxidation that connects DMS to sulfate aerosol is less well understood. Recent laboratory measurements suggest that heterogeneous and photochemical reactions occurring at the air-sea interface can also lead to the production and emission of a wide array of reactive VOC. When laboratory-based measurements are used to derive global scale emissions, the calculated sea-to-air fluxes of reactive VOC generated from heterogeneous and photochemical processes are comparable or larger in magnitude to the sea-to-air flux of DMS. It is not yet clear how the mechanisms proposed in these laboratory experiments translate to atmospheric conditions. The proposed abiotic emissions are also a potential source of VOC in regions of low biological activity, which carries important implications for regional and global modeling.This Account reviews recent laboratory and field experiments of biotic and abiotic ocean VOC emissions, with a specific focus on exploring open questions related to proposed abiotic reactive VOC emissions and the impact of including a large, abiotic VOC emission source on atmospheric oxidants and aerosol particles. To date, abiotic emissions are not typically included in global chemical transport models. The proposed abiotic emissions mechanisms discussed here have the potential to drive significant changes to current understanding of chemistry in the marine atmosphere if present at the magnitudes suggested by laboratory studies. In order to validate their proposed significance, a coordinated set of laboratory, field, and modeling studies under ocean-relevant conditions are necessary.

The Impact of Aerosol Particle Mixing State on the Hygroscopicity of Sea Spray Aerosol.

Aerosol particles influence global climate by determining cloud droplet number concentrations, brightness, and lifetime. Primary aerosol particles, such as those produced from breaking waves in the ocean, display large particle-particle variability in chemical composition, morphology, and physical phase state, all of which affect the ability of individual particles to accommodate water and grow into cloud droplets. Despite such diversity in molecular composition, there is a paucity of methods available to assess how particle-particle variability in chemistry translates to corresponding differences in aerosol hygroscopicity. Here, an approach has been developed that allows for characterization of the distribution of aerosol hygroscopicity within a chemically complex population of atmospheric particles. This methodology, when applied to the interpretation of nascent sea spray aerosol, provides a quantitative framework for connecting results obtained using molecular mimics generated in the laboratory with chemically complex ambient aerosol. We show that nascent sea spray aerosol, generated in situ in the Atlantic Ocean, displays a broad distribution of particle hygroscopicities, indicative of a correspondingly broad distribution of particle chemical compositions. Molecular mimics of sea spray aerosol organic material were used in the laboratory to assess the volume fractions and molecular functionality required to suppress sea spray aerosol hygroscopicity to the extent indicated by field observations. We show that proper accounting for the distribution and diversity in particle hygroscopicity and composition are important to the assessment of particle impacts on clouds and global climate.