Identification of a Female-Produced Sex Attractant Pheromone of the Winter Firefly, Photinus corruscus Linnaeus (Coleoptera: Lampyridae).

Firefly flashes are well-known visual signals used by these insects to find, identify, and choose mates. However, many firefly species have lost the ability to produce light as adults. These "unlighted" species generally lack developed adult light organs, are diurnal rather than nocturnal, and are believed to use volatile pheromones acting over a distance to locate mates. While cuticular hydrocarbons, which may function in mate recognition at close range, have been examined for a handful of the over 2000 extant firefly species, no volatile pheromone has ever been identified. In this study, using coupled gas chromatography - electroantennographic detection, we detected a single female-emitted compound that elicited antennal responses from wild-caught male winter fireflies, Photinus corruscus. The compound was identified as (1S)-exo-3-hydroxycamphor (hydroxycamphor). In field trials at two sites across the species' eastern North American range, large numbers of male P. corruscus were attracted to synthesized hydroxycamphor, verifying its function as a volatile sex attractant pheromone. Males spent more time in contact with lures treated with synthesized hydroxycamphor than those treated with solvent only in laboratory two-choice assays. Further, using single sensillum recordings, we characterized a pheromone-sensitive odorant receptor neuron in a specific olfactory sensillum on male P. corruscus antennae and demonstrated its sensitivity to hydroxycamphor. Thus, this study has identified the first volatile pheromone and its corresponding sensory neuron for any firefly species, and provides a tool for monitoring P. corruscus populations for conservation and further inquiry into the chemical and cellular bases for sexual communication among fireflies.

Unintended Consequences of Air Cleaning Chemistry.

Amplified interest in maintaining clean indoor air associated with the airborne transmission risks of SARS-CoV-2 have led to an expansion in the market for commercially available air cleaning systems. While the optimal way to mitigate indoor air pollutants or contaminants is to control (remove) the source, air cleaners are a tool for use when absolute source control is not possible. Interventions for indoor air quality management include physical removal of pollutants through ventilation or collection on filters and sorbent materials, along with chemically reactive processes that transform pollutants or seek to deactivate biological entities. This perspective intends to highlight the perhaps unintended consequences of various air cleaning approaches via indoor air chemistry. Introduction of new chemical agents or reactive processes can initiate complex chemistry that results in the release of reactive intermediates and/or byproducts into the indoor environment. Since air cleaning systems are often continuously running to maximize their effectiveness and most people spend a vast majority of their time indoors, human exposure to both primary and secondary products from air cleaners may represent significant exposure risk. This Perspective highlights the need for further study of chemically reactive air cleaning and disinfection methods before broader adoption.

Cooking, Bleach Cleaning, and Air Conditioning Strongly Impact Levels of HONO in a House.

The relative importance of common activities on indoor nitrous acid (HONO) mixing ratios was explored during high time resolution, month-long measurements by chemical ionization mass spectrometry in a previously unoccupied house. Indoor HONO varied from 0.2 to 84.0 ppb (mean: 5.5 ppb; median 3.8 ppb), an order of magnitude higher than simultaneously measured outdoor values, indicating important indoor sources. They agree well with simultaneous measurements of HONO by Laser-Photofragmentation/Laser-Induced Fluorescence. Before any combustion activities, the mixing ratio of 3.0 ± 0.3 ppb is indicative of secondary sources such as multiphase formation from NO2. Cooking (with propane gas), especially the use of an oven, led to significant enhancements up to 84 ppb, with elevated mixing ratios persisting for a few days due to slow desorption from indoor surface reservoirs. Floor bleach cleaning led to prolonged, substantial decreases of up to 71-90% due to reactive processes. Air conditioning modulated HONO mixing ratios driven by condensation to wet surfaces in the AC unit. Enhanced ventilation also significantly lowered mixing ratios. Other conditions including human occupancy, ozone addition, and cleaning with terpene, natural product, and vinegar cleaners had a much smaller influence on HONO background levels measured following these activities.

Indoor Surface Chemistry: Developing a Molecular Picture of Reactions on Indoor Interfaces.

Chemical reactions on indoor surfaces play an important role in air quality in indoor environments, where humans spend 90% of their time. We focus on the challenges of understanding the complex chemistry that takes place on indoor surfaces and identify crucial steps necessary to gain a molecular-level understanding of environmental indoor surface chemistry: (1) elucidate key surface reaction mechanisms and kinetics important to indoor air chemistry, (2) define a range of relevant and representative surfaces to probe, and (3) define the drivers of surface reactivity, particularly with respect to the surface composition, light, and temperature. Within the drivers of surface composition are the roles of adsorbed/absorbed water associated with indoor surfaces and the prevalence, inhomogeneity, and properties of secondary organic films that can impact surface reactivity. By combining laboratory studies, field measurements, and modeling we can gain insights into the molecular processes necessary to further our understanding of the indoor environment.

Surface reservoirs dominate dynamic gas-surface partitioning of many indoor air constituents.

Human health is affected by indoor air quality. One distinctive aspect of the indoor environment is its very large surface area that acts as a poorly characterized sink and source of gas-phase chemicals. In this work, air-surface interactions of 19 common indoor air contaminants with diverse properties and sources were monitored in a house using fast-response, on-line mass spectrometric and spectroscopic methods. Enhanced-ventilation experiments demonstrate that most of the contaminants reside in the surface reservoirs and not, as expected, in the gas phase. They participate in rapid air-surface partitioning that is much faster than air exchange. Phase distribution calculations are consistent with the observations when assuming simultaneous equilibria between air and large weakly polar and polar absorptive surface reservoirs, with acid-base dissociation in the polar reservoir. Chemical exposure assessments must account for the finding that contaminants that are fully volatile under outdoor air conditions instead behave as semivolatile compounds indoors.

Indoor Illumination of Terpenes and Bleach Emissions Leads to Particle Formation and Growth.

Application of chlorine bleach solution (major component sodium hypochlorite, NaOCl) in indoor environments leads to the emission of gaseous hypochlorous acid (HOCl) and chlorine (Cl2), both of which are strong oxidants. In contrast to the outdoor atmosphere, where mixing ratios of HOCl and Cl2 tend to be low (10s-100s of ppt), indoor HOCl and Cl2 can reach high levels during cleaning activities (100s of ppb or higher). HOCl and Cl2 may react with unsaturated organic compounds on indoor surfaces and in indoor air. In this study, we studied the reaction of limonene, one of the most common indoor volatile organic compounds (VOCs) arising from use of cleaning products, fragrance, and air fresheners, with HOCl and Cl2 in an environmental chamber. A dark reaction was observed between limonene and HOCl/Cl2 leading to gas-phase reaction products that were investigated using proton transfer reaction mass spectrometry (PTR-MS). With subsequent exposure to indoor fluorescent lights or diffuse sunlight through a nearby window, a substantial mass loading of secondary particles were formed with an averaged mass yield of 40% relative to the amount of limonene consumed. Aerosol mass spectrometry (AMS) measurements indicate a large contribution of particulate chlorine species. Electrospray ionization mass spectrometry (ESI-MS) analysis of filter-collected particles indicates the formation of high molecular weight products. This is the first study of the oxidation of limonene with HOCl and Cl2, and it illustrates the potential for particle formation to occur with indoor lighting during the use of common cleaning products.

Sources of isocyanic acid (HNCO) indoors: a focus on cigarette smoke.

The sources and sinks of isocyanic acid (HNCO), a toxic gas, in indoor environments are largely uncharacterized. In particular, cigarette smoke has been identified as a significant source. In this study, controlled smoking of tobacco cigarettes was investigated in both an environmental chamber and a residence in Toronto, Canada using an acetate-CIMS. The HNCO emission ratio from side-stream cigarette smoke was determined to be 2.7 (±1.1) × 10-3 ppb HNCO/ppb CO. Side-stream smoke from a single cigarette introduced a large pulse of HNCO to the indoor environment, increasing the HNCO mixing ratio by up to a factor of ten from background conditions of 0.15 ppb. Although there was no evidence for photochemical production of HNCO from cigarette smoke in the residence, it was observed in the environmental chamber via oxidation by the hydroxyl radical (1.1 × 107 molecules per cm3), approximately doubling the HNCO mixing ratio after 30 minutes of oxidation. Oxidation of cigarette smoke by O3 (15 ppb = 4.0 × 1017 molecules per cm3) and photo-reaction with indoor fluorescent lights did not produce HNCO. By studying the temporal profiles of both HNCO and CO after smoking, it is inferred that gas-to-surface partitioning of HNCO acts as an indoor loss pathway. Even in the absence of smoking, the indoor HNCO mixing ratios in the Toronto residence were elevated compared to concurrent outdoor measurements by approximately a factor of two.

Selective Uptake of Third-Hand Tobacco Smoke Components to Inorganic and Organic Aerosol Particles.

Third-hand smoke (THS) is an emerging route of exposure to tobacco smoke in the indoor environment. Few studies have investigated the chemical behavior of THS, although initial findings suggest that semivolatile components of THS can partition to indoor aerosol. By exposing single-component particles to THS in an environmental chamber, this study demonstrates a pronounced dependence of THS uptake on aerosol composition. First, it was found that primarily reduced nitrogen compounds (that produced C xH yN z+ ion signal) in THS partitioned strongly to acidic ammoniated sulfate particles, whereas overall THS uptake to more pH-neutral sodium sulfate particles was minimal. Second, THS uptake to pure hydrocarbon particles (squalane) was even greater than to ammoniated sulfate particles with the uptake arising from mainly C xH y compounds. The greater uptake of THS to squalane was mostly driven by the dominant fraction of C xH y compounds in the side stream cigarette smoke aerosol, the composition of which is likely to be broadly similar to THS in these experiments. Third, oxygenated organic particles (sucrose) and solid ammonium sulfate particles showed minimal uptake. These results indicate that particulate THS inhalation exposure will be strongly dependent on the chemical nature of the particles present in the indoor environment.

Evidence for Gas-Surface Equilibrium Control of Indoor Nitrous Acid.

Nitrous acid (HONO) is an important component of indoor air as a photolabile precursor to hydroxyl radicals and has direct health effects. HONO concentrations are typically higher indoors than outdoors, although indoor concentrations have proved challenging to predict using box models. In this study, time-resolved measurements of HONO and NO2 in a residence showed that [HONO] varied relatively weakly over contiguous periods of hours, while [NO2] fluctuated in association with changes in outdoor [NO2]. Perturbation experiments were performed in which indoor HONO was depleted or elevated and were interpreted using a two-compartment box model. To reproduce the measurements, [HONO] had to be predicted using persistent source and sink processes that do not directly involve NO2, suggesting that HONO was in equilibrium with indoor surfaces. Production of gas phase HONO directly from conversion of NO2 on surfaces had a weak influence on indoor [HONO] during the time of the perturbations. Highly similar temporal responses of HONO and semivolatile carboxylic acids to ventilation of the residence along with the detection of nitrite on indoor surfaces support the concept that indoor HONO mixing ratios are controlled strongly by gas-surface equilibrium.

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 (O3), hydroxyl radicals (OH) and indoor fluorescent lights. Aerosol mass concentrations increased by 13-18% upon exposure to 15 ppb O3 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-3). During OH oxidation, however, UFP formed only when the primary particle concentration was relatively low (<130 µg m-3) and the OH concentration was high (∼1.1 × 107 molecules cm-3). Online aerosol composition measurements show that oxygen- and nitrogen- containing species were formed during oxidation. Gas phase oxidation of NO to NO2 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 (∼107 molecules cm-3), and is therefore less likely to have an impact on indoor aerosol associated with cigarette smoke.

The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles.

The oceans represent a significant global source of atmospheric aerosols. Sea spray aerosol (SSA) particles comprise sea salts and organic species in varying proportions. In addition to size, the overall composition of SSA particles determines how effectively they can form cloud droplets and ice crystals. Thus, understanding the factors controlling SSA composition is critical to predicting aerosol impacts on clouds and climate. It is often assumed that submicrometer SSAs are mainly formed by film drops produced from bursting bubble-cap films, which become enriched with hydrophobic organic species contained within the sea surface microlayer. In contrast, jet drops formed from the base of bursting bubbles are postulated to mainly produce larger supermicrometer particles from bulk seawater, which comprises largely salts and water-soluble organic species. However, here we demonstrate that jet drops produce up to 43% of total submicrometer SSA number concentrations, and that the fraction of SSA produced by jet drops can be modulated by marine biological activity. We show that the chemical composition, organic volume fraction, and ice nucleating ability of submicrometer particles from jet drops differ from those formed from film drops. Thus, the chemical composition of a substantial fraction of submicrometer particles will not be controlled by the composition of the sea surface microlayer, a major assumption in previous studies. This finding has significant ramifications for understanding the factors controlling the mixing state of submicrometer SSA particles and must be taken into consideration when predicting SSA impacts on clouds and climate.

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.

Sea Spray Aerosol Structure and Composition Using Cryogenic Transmission Electron Microscopy.

The composition and surface properties of atmospheric aerosol particles largely control their impact on climate by affecting their ability to uptake water, react heterogeneously, and nucleate ice in clouds. However, in the vacuum of a conventional electron microscope, the native surface and internal structure often undergo physicochemical rearrangement resulting in surfaces that are quite different from their atmospheric configurations. Herein, we report the development of cryogenic transmission electron microscopy where laboratory generated sea spray aerosol particles are flash frozen in their native state with iterative and controlled thermal and/or pressure exposures and then probed by electron microscopy. This unique approach allows for the detection of not only mixed salts, but also soft materials including whole hydrated bacteria, diatoms, virus particles, marine vesicles, as well as gel networks within hydrated salt droplets-all of which will have distinct biological, chemical, and physical processes. We anticipate this method will open up a new avenue of analysis for aerosol particles, not only for ocean-derived aerosols, but for those produced from other sources where there is interest in the transfer of organic or biological species from the biosphere to the atmosphere.

Sea spray aerosol as a unique source of ice nucleating particles.

Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratory-generated SSA, when normalized to typical total aerosol number concentrations in the marine boundary layer, agree well with measurements from diverse regions over the oceans. Data in the present study are also in accord with previously published INP measurements made over remote ocean regions. INP number concentrations active within liquid water droplets increase exponentially in number with a decrease in temperature below 0 °C, averaging an order of magnitude increase per 5 °C interval. The plausibility of a strong increase in SSA INP emissions in association with phytoplankton blooms is also shown in laboratory simulations. Nevertheless, INP number concentrations, or active site densities approximated using "dry" geometric SSA surface areas, are a few orders of magnitude lower than corresponding concentrations or site densities in the surface boundary layer over continental regions. These findings have important implications for cloud radiative forcing and precipitation within low-level and midlevel marine clouds unaffected by continental INP sources, such as may occur over the Southern Ocean.

Advancing Model Systems for Fundamental Laboratory Studies of Sea Spray Aerosol Using the Microbial Loop.

Sea spray aerosol (SSA) particles represent one of the most abundant surfaces available for heterogeneous reactions to occur upon and thus profoundly alter the composition of the troposphere. In an effort to better understand tropospheric heterogeneous reaction processes, fundamental laboratory studies must be able to accurately reproduce the chemical complexity of SSA. Here we describe a new approach that uses microbial processes to control the composition of seawater and SSA particle composition. By inducing a phytoplankton bloom, we are able to create dynamic ecosystem interactions between marine microorganisms, which serve to alter the organic mixtures present in seawater. Using this controlled approach, changes in seawater composition become reflected in the chemical composition of SSA particles 4 to 10 d after the peak in chlorophyll-a. This approach for producing and varying the chemical complexity of a dominant tropospheric aerosol provides the foundation for further investigations of the physical and chemical properties of realistic SSA particles under controlled conditions.

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.

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.

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.

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(+), K(+), Mg(2+), and Ca(2+)) 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.