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Squalene is a major skin oil lipid which can react with ozone forming a range of products including carbonyls, carboxylic acids, hydroxy ketones, secondary ozonides and hydroperoxides. Previous experimental studies have shown that the yield of these products depends on relative humidity. A new mechanism is developed which treats the reaction of ozone with carbon–carbon double bonds and the subsequent reactions of the Criegee intermediates forming a range of products in both condensed and gas phases. The mechanism is included in kinetic models for a variety of ozonolysis reaction systems including pure squalene particles, squalene and skin oil films, clothing, and skin covered by clothing. The models reproduce experimental measurements reasonably well using relatively consistent parameters, providing insights into the important reactions and processes controlling the concentrations of different species. In general, gas-phase secondary carbonyl product concentrations increase significantly as a function of relative humidity due to their formation from the reaction of Criegee intermediates with water, while carboxylic acids and hydroxy ketone concentrations decrease. For example, human exposure to gas-phase 6-methyl-5-hepten-2-one can increase by approximately a factor of two as the relative humidity increases from 10% to 95%. The model can also reproduce the decay of carboxylic acids in skin oil due to their reaction with Criegee intermediates. Discrepancies between some of the measurements and model outputs indicate that in addition to impacting chemistry, relative humidity may affect other processes such as partitioning to surfaces and condensed-phase diffusion.

Adsorption and desorption of volatile organic compounds (VOCs) on indoor material surfaces can impact VOC concentrations in indoor air. In this study, we investigate the adsorption and desorption kinetics of limonene and one of its oxidation products, carvone, at 297 ± 1 K using in situ Fourier transform infrared (FTIR) spectroscopy. In particular, the adsorption and desorption kinetics of limonene and carvone on two model indoor-relevant surfaces, TiO2(a component of paint and self-cleaning surfaces) and SiO2(a model for window glass), are compared at low relative humidity as well as at higher relative humidity. Carvone readily partitions to both surfaces with slower desorption kinetics compared to limonene. Under dry conditions, the desorption kinetics of limonene is about 40 times faster than that of carvone from TiO2, and the desorption kinetics of limonene and carvone from TiO2are about two and four times slower than on SiO2, respectively. Under high relative humidity conditions, the presence of adsorbed water on both TiO2and SiO2surfaces generally increases the desorption kinetics of limonene yet has no effect on the desorption kinetics of carvone. The K2-SURF kinetics model has been previously applied to limonene adsorption/desorption on SiO2, and here, it is used to obtain a detailed mechanism for limonene interactions on TiO2as a function of relative humidity to explain the observed kinetics. Importantly, the combined experimental results with kinetic modeling and classical and ab initiomolecular dynamics simulations provide mechanistic insights into the heterogeneous interactions of volatile organic compounds on indoor-relevant surfaces and implications for indoor air quality.

Oxygenated semivolatile organic compounds are present in indoor air due to the oxidation of monoterpenes and other hydrocarbons. The partitioning of these compounds to indoor surfaces and the formation of organic thin films are of great interest as these surfaces become potential reservoirs for these compounds affecting indoor air composition. Here, we have investigated the interaction of carvone, a limonene oxidation product, with hydroxylated SiO2surfaces at 297 ± 1 K with FTIR spectroscopy. The detailed surface interactions were understood through both force field-based molecular dynamics (MD), ab initio molecular dynamics (AIMD) simulations, and electronic structure calculations. The adsorption/desorption kinetics of carvone on hydroxylated SiO2have been measured as a function of relative humidity. The desorption kinetics of carvone from the SiO2surface are slow, approximately 30 times slower when compared to limonene under dry conditions. Molecular dynamics (MD) simulations reveal that carvone forms O–H hydrogen bonding (carbonyl O to HO–Si) with the isolated hydroxyl groups and oxygen silicon associations (carbonyl O to Si–O–Si) with siloxane bridges that are also on the SiO2surface. A kinetic model was applied to further examine the carvone adsorption and desorption kinetics; the experimental measurements can be reproduced by assuming that some carvone molecules become trapped in pores between the SiO2particles. Interestingly, relative humidity does not change the desorption kinetics of carvone from the SiO2surface. Instead, water molecules adsorb onto the preadsorbed carvone, which hydrates the organic-coated surface. Overall, this study shows how carvone, an oxygenated organic compound, interacts with indoor relevant surfaces and the impact of relative humidity on these interactions. It also demonstrates how chemical transformations (e.g., oxidation) in indoor environments can play an important role in how molecules partition to surfaces and interact with condensed phase water.

Long-term manned space-exploration missions and the permanence of human colonies on orbital stations or planetary habitats will require the regeneration of resources onboard or in-situ. Bioregenerative Life Support Systems (BLSSs) are artificial environments where different compartments, involving both living organisms and physical-chemical processes, are integrated to achieve a safe, self-regulating, and chemically balanced Earth-like environment to support human life. Higher plants are key elements of such systems and Space greenhouses represent the producers’ compartment. Growing plants in Space requires the knowledge of their growth responses not only to all environmental factors acting on Earth, but also to specific Space constraints such as altered gravity, ionizing radiations and confined volume. Moreover, cultivation techniques need to be adjusted considering such limitations. The type and intensity of environmental factors to be taken into account depend on the mission scenarios. Here, we summarize constraints and opportunities of cultivating higher plants in Space to regenerate resources and produce fresh food onboard. Both biological and agro-technological issues are considered briefly going through experiments both ground-based on Earth and in Space.

Nitrous acid (HONO) is an important gaseous pollutant contributing to indoor air pollution because it causes adverse health effects and is the main source of hydroxyl radicals (OH). Here, we present direct measurements of HONO produced through light-induced heterogeneous reactions of NO2with grime adsorbed on glass window. The uptake coefficients of NO2[γ(NO2)] on the glass plates from the kitchen increased markedly from (2.3 ± 0.1) × 10–6at 0% RH to (4.1 ± 0.5) × 10–6at 90% RH. We report a significant quantity of daytime HONO produced in the kitchen, compared to the living room and bedroom. Kinetic modeling suggests that phase state and bulk diffusivity play important roles in the NO2uptake; the best fit to the measured uptake coefficients is obtained with fixed diffusion coefficients. Photon scattering may be occurring at the surface of the films, leading to enhanced photon-excitation rates of polycyclic aromatic hydrocarbons. By taking these effects into account, the results from this study indicate that the HONO yields obtained in this study can explain the missing HONO in the photochemical models describing the indoor air chemistry.

The reaction of ozone with iodide in the ocean is a major ozone dry deposition pathway, as well as an important source of reactive iodine to the marine troposphere. Few prior laboratory experiments have been conducted with environmentally relevant ozone mixing ratios and iodide concentrations, leading to uncertainties in the rate of the reaction under marine boundary layer conditions. As well, there remains disagreement in the literature assessment of the relative contributions of an interfacial reaction via ozone adsorbed to the ocean surface versus a bulk reaction with dissolved ozone. In this study, we measure the uptake coefficient of ozone over a buffered, pH 8 salt solution replicating the concentrations of iodide, bromide, and chloride in the ocean over an ozone mixing ratio of 60–500 ppb. Due to iodide depletion in the solution, the measured ozone uptake coefficient is dependent on the exposure time of the solution to ozone and its mixing ratio. A kinetic multilayer model confirms that iodide depletion is occurring not only within ozone’s reactodiffusive depth, which is on the order of microns for environmental conditions, but also deeper into the solution as well. Best model-measurement agreement arises when some degree of nondiffusive mixing is occurring in the solution, transporting iodide from deeper in the solution to a thin, diffusively mixed upper layer. If such mixing occurs rapidly in the environment, iodide depletion is unlikely to reduce ozone dry deposition rates. Unrealistically high bulk-to-interface partitioning of iodide is required for the model to predict a substantial interfacial component to the reaction, indicating that the Langmuir–Hinshelwood mechanism is not dominant under environmental conditions.

Isoprene hydroxy hydroperoxides (ISOPOOH) formed by the photooxidation of isoprene under low-NO conditions play an important role in the formation and evolution of secondary organic aerosols, yet multiphase processes of ISOPOOH are poorly understood. By applying electron paramagnetic resonance spectroscopy, we observe that ISOPOOH undergoes aqueous-phase decomposition upon interacting with Fe(II) ions to form OH and organic radicals at room temperature. To reproduce the measured dependence of OH formation on the Fe concentrations by kinetic modeling, we postulate that Fe(II) ions react with ISOPOOH via Fenton-like reactions to form OH radicals with a rate constant of 7.3 × 10–18cm3s–1. At low concentrations, oxalate forms monocomplexes with Fe(II) ions, which can promote OH formation by ISOPOOH. However, at high concentrations, oxalate scavenges OH radicals, thereby lowering aqueous OH concentrations. These findings provide new insight for the atmospheric fate of ISOPOOH and reactive oxygen species generation in the aqueous phase.

We performed classical molecular dynamics simulations to quantify and understand the nonreactive, dermal uptake of volatile organic compounds formed during the ozonolysis of human skin oils. Our results include surface accommodation coefficients, partitioning constants, bulk diffusivities, and desorption lifetimes. These parameters were used to improve and to constrain the kinetic multilayer model of the surface and bulk chemistry of skin (KM-SUB-Skin). By comparing common outputs (bulk accommodation coefficients), we cross-validate the two approaches and, thus, increase the level of trust in their predictions relevant to indoor air chemistry.

We report elevated levels of gaseous inorganic chlorinated and nitrogenated compounds in indoor air while cleaning with a commercial bleach solution during the House Observations of Microbial and Environmental Chemistry field campaign in summer 2018. Hypochlorous acid (HOCl), chlorine (Cl2), and nitryl chloride (ClNO2) reached part-per-billion by volume levels indoors during bleach cleaning—several orders of magnitude higher than typically measured in the outdoor atmosphere. Kinetic modeling revealed that multiphase chemistry plays a central role in controlling indoor chlorine and reactive nitrogen chemistry during these periods. Cl2production occurred via heterogeneous reactions of HOCl on indoor surfaces. ClNO2and chloramine (NH2Cl, NHCl2, NCl3) production occurred in the applied bleach via aqueous reactions involving nitrite (NO2–) and ammonia (NH3), respectively. Aqueous-phase and surface chemistry resulted in elevated levels of gas-phase nitrogen dioxide (NO2). We predict hydroxyl (OH) and chlorine (Cl) radical production during these periods (106and 107molecules cm–3s–1, respectively) driven by HOCl and Cl2photolysis. Ventilation and photolysis accounted for <50% and <0.1% total loss of bleach-related compounds from indoor air, respectively; we conclude that uptake to indoor surfaces is an important additional loss process. Indoor HOCl and nitrogen trichloride (NCl3) mixing ratios during bleach cleaning reported herein are likely detrimental to human health.

Reactive oxygen species (ROS) play a central role in adverse health effects of air pollutants. Respiratory deposition of fine air particulate matter can lead to the formation of ROS in epithelial lining fluid, potentially causing oxidative stress and inflammation. Secondary organic aerosols (SOA) account for a large fraction of fine particulate matter, but their role in adverse health effects is unclear. Here, we quantify and compare the ROS yields and oxidative potential of isoprene, β-pinene, and naphthalene SOA in water and surrogate lung fluid (SLF). In pure water, isoprene and β-pinene SOA were found to produce mainly OH and organic radicals, whereas naphthalene SOA produced mainly H2O2and O2•-. The total molar yields of ROS of isoprene and β-pinene SOA were 11.8% and 8.2% in water and decreased to 8.5% and 5.2% in SLF, which can be attributed to ROS removal by lung antioxidants. A positive correlation between the total peroxide concentration and ROS yield suggests that organic (hydro)peroxides may play an important role in ROS formation from biogenic SOA. The total molar ROS yields of naphthalene SOA was 1.7% in water and increased to 11.3% in SLF. This strong increase is likely due to redox reaction cycles involving environmentally persistent free radicals (EPFR) or semiquinones, antioxidants, and oxygen, which may promote the formation of H2O2and the adverse health effects of anthropogenic SOA from aromatic precursors.

The kinetics of heterogeneous HO2uptake onto meteoric smoke particles (MSPs) has been studied in the laboratory using analogues of MSP aerosol entrained into a flow tube. The uptake coefficient, γ, was determined on synthetic amorphous olivine (MgFeSiO4) to be (6.9 ± 1.2) × 10−2at a relative humidity (RH) of 10%. On forsterite (Mg2SiO4), γ= (4.3 ± 0.4) × 10−3at RH = 11.6% and (7.3 ± 0.4) × 10−2at RH = 9.9% on fayalite (Fe2SiO4). These results indicate that Fe plays a more important mechanistic role than Mg in the removal of HO2from the gas phase. Electronic structure calculations show that Fe atoms exposed at the particle surface provide a catalytic site where HO2is converted to H2O2via an Eley‐Rideal mechanism, but this does not occur on exposed surface Mg atoms. The impact of this heterogeneous process in the middle atmosphere was then investigated using a whole atmosphere chemistry‐climate model which incorporates a microphysical treatment of MSPs. Using a global MSP production rate from meteoric ablation of 44 t/day, heterogeneous uptake (with γ= 0.2) on MSPs significantly alters the HOxbudget in the nighttime polar vortex. This impact is highly latitude dependent and thus could not be confirmed using currently available satellite measurements of HO2, which are largely unavailable at latitudes greater than 70°. This study investigates the interaction between extra‐terrestrial material and one of the important reactant species ‐ the hydroperoxy radical HO2‐ in the stratosphere and mesosphere. Roughly 6 tonnes of metallic vapors are injected into the upper atmosphere every day from interplanetary dust particles entering the atmosphere at high speeds (up to 155,000 mph). The vapors then condense into tiny particles, a few nanometers in size, known as meteoric smoke. These particles are transported to the winter polar region, and then descend from around 80 to 30 km during the polar night. It is in this dark region of the atmosphere where the smoke has a significant effect on the HO2concentration, with a knock‐on effect for ozone. In this study, the rate of removal of HO2on meteoric smoke analog particles was measured in the laboratory. The lab results were then incorporated into a global chemistry‐climate model to demonstrate these atmospheric impacts. HO2uptake coefficients measured on synthetic amorphous olivine particlesExposed surface Fe atoms appear to catalyze HO2removal to form H2O2Uptake on meteoric smoke significantly impacts the HO2atmospheric abundance over the winter poles

High Mountain Asia is impacted by extreme monsoonal rainfall that triggers landslides in large proportions relative to global distributions, resulting in substantial human impacts and damage to infrastructure each year. Previous landslide research has qualitatively estimated how patterns in landslide activity may change based on climate change scenarios. We present the first quantitative view of potential modulation in future landslide activity over the High Mountain Asia region leveraging a new landslide hazard model and precipitation data from satellite and Global Climate Model sources. In doing so, we find that the rate of increase in landslide activity at the end of the century is expected to be greatest over areas covered by current glaciers and glacial lakes, potentially exacerbating the impacts of cascading hazards on populations downstream. This work demonstrates the potential of Global Climate Models and satellite‐based precipitation estimates to characterize landslide hazards at time scales affected by climate change. High Mountain Asia is home to both monsoonal rains and the largest concentration of glaciers outside the North and South Poles. With climate change, heavy rainfall will increase, especially in mountains near glaciers and glacial lakes. This will make landslides more likely and could present new hazards of landslides releasing a wall of water from glacial lakes, impacting communities and infrastructure are located downstream. We present the first quantitative view of how landslide activity may change within High Mountain Asia resulting from changes in extreme precipitationWe find that the rate of increase in landslide activity at the end of the century is expected to be greatest over areas covered by current glaciers and glacial lakesWe show how Global Climate Models and satellite observations can be used to model landslide impacts at time scales affected by climate change