Conflicts of Interest in the Assessment of Chemicals, Waste, and Pollution.

Pollution by chemicals and waste impacts human and ecosystem health on regional, national, and global scales, resulting, together with climate change and biodiversity loss, in a triple planetary crisis. Consequently, in 2022, countries agreed to establish an intergovernmental science-policy panel (SPP) on chemicals, waste, and pollution prevention, complementary to the existing intergovernmental science-policy bodies on climate change and biodiversity. To ensure the SPP's success, it is imperative to protect it from conflicts of interest (COI). Here, we (i) define and review the implications of COI, and its relevance for the management of chemicals, waste, and pollution; (ii) summarize established tactics to manufacture doubt in favor of vested interests, i.e., to counter scientific evidence and/or to promote misleading narratives favorable to financial interests; and (iii) illustrate these with selected examples. This analysis leads to a review of arguments for and against chemical industry representation in the SPP's work. We further (iv) rebut an assertion voiced by some that the chemical industry should be directly involved in the panel's work because it possesses data on chemicals essential for the panel's activities. Finally, (v) we present steps that should be taken to prevent the detrimental impacts of COI in the work of the SPP. In particular, we propose to include an independent auditor's role in the SPP to ensure that participation and processes follow clear COI rules. Among others, the auditor should evaluate the content of the assessments produced to ensure unbiased representation of information that underpins the SPP's activities.

Biomass combustion produces ice-active minerals in biomass-burning aerosol and bottom ash.

Ice nucleation and the resulting cloud glaciation are significant atmospheric processes that affect the evolution of clouds and their properties including radiative forcing and precipitation, yet the sources and properties of atmospheric ice nucleants are poorly constrained. Heterogeneous ice nucleation caused by ice-nucleating particles (INPs) enables cloud glaciation at temperatures above the homogeneous freezing regime that starts near -35 °C. Biomass burning is a significant global source of atmospheric particles and a highly variable and poorly understood source of INPs. The nature of these INPs and how they relate to the fuel composition and its combustion are critical gaps in our understanding of the effects of biomass burning on the environment and climate. Here we show that the combustion process transforms inorganic elements naturally present in the biomass (not soil or dust) to form potentially ice-active minerals in both the bottom ash and emitted aerosol particles. These particles possess ice-nucleation activities high enough to be relevant to mixed-phase clouds and are active over a wide temperature range, nucleating ice at up to -13 °C. Certain inorganic elements can thus serve as indicators to predict the production of ice nucleants from the fuel. Combustion-derived minerals are an important but understudied source of INPs in natural biomass-burning aerosol emissions in addition to lofted primary soil and dust particles. These discoveries and insights should advance the realistic incorporation of biomass-burning INPs into atmospheric cloud and climate models. These mineral components produced in biomass-burning aerosol should also be studied in relation to other atmospheric chemistry processes, such as facilitating multiphase chemical reactions and nutrient availability.

Aerosol Optical Tweezers Elucidate the Chemistry, Acidity, Phase Separations, and Morphology of Atmospheric Microdroplets.

ConspectusAerosol particles represent unique chemical environments because of their high surface area-to-volume ratio that promotes the effects of interfacial chemistry in confined environments. Properties such as viscosity, diffusivity, water content, pH, and morphology-following liquid-liquid phase separation-can strongly alter how a particle interacts with condensable vapors and reactive trace gases, thus modifying its continual evolution and environmental effects. Our understanding of this chemical evolution of atmospheric particulate matter and its environmental impacts is largely limited by our ability to directly observe how these critical particle properties respond to the addition or reactive uptake of new chemical components. Aerosol optical tweezers (AOT) stably trap particles in focused laser beams, providing positional control and the retrieval of many of these critical properties required to understand and predict the chemistry of aerosolized microdroplets. The analytical power of the AOT stems from the retrieval of the cavity-enhanced Raman spectrum induced by the trapping laser. Analysis of the whispering gallery modes (WGMs) that resonate as a standing wave around the droplet's interface, provide high accuracy measurements of the droplet's size, refractive index (and thus a measurement of composition), and can distinguish between core-shell, partially engulfed, and homogeneous morphologies. We have advanced the ability to determine the properties of the core and shell phases in biphasic droplets, including obtaining high-accuracy pH measurements. These capabilities were applied to perform AOT physical chemistry experiments on authentic secondary organic aerosol (SOA) produced directly in the AOT chamber by ozonolysis of terpene vapors. The propensity of the SOA to phase separate as a shell from a wide range of nonpolar to polar core phases was observed, along with the discovery of a stable emulsified state of SOA particles in an aqueous salt droplet. Micron-thick SOA shells did not impede the gain or loss of water or squalane from the core to the surrounding air, indicating no significant diffusional limitations to condensational growth or partitioning even under dry conditions. These experiments formed the foundation of a new framework that predicts how the phase-separated morphology of complex aerosols containing organic carbon evolves during continual atmospheric oxidation processes. Increases in oxidation state will quickly drive conversion from a partially engulfed to core-shell morphology that has dramatically different chemical reactivity since the core phase is completely concealed by the shell. The recent advances in the experimental capabilities of the AOT technique such as presented here enable novel experimental methodologies that provide insights into the chemistry and multidimensional properties of aerosol microdroplets, and how these coevolve and respond to continual chemical reactions.

Much stronger tundra methane emissions during autumn freeze than spring thaw.

Warming in the Arctic has been more apparent in the non-growing season than in the typical growing season. In this context, methane (CH4 ) emissions in the non-growing season, particularly in the shoulder seasons, account for a substantial proportion of the annual budget. However, CH4 emissions in spring and autumn shoulders are often underestimated by land models and measurements due to limited data availability and unknown mechanisms. This study investigates CH4 emissions during spring thaw and autumn freeze using eddy covariance CH4 measurements from three Arctic sites with multi-year observations. We find that the shoulder seasons contribute to about a quarter (25.6 ± 2.3%, mean ± SD) of annual total CH4 emissions. Our study highlights the three to four times higher contribution of autumn freeze CH4 emission to total annual emission than that of spring thaw. Autumn freeze exhibits significantly higher CH4 flux (0.88 ± 0.03 mg m-2  hr-1 ) than spring thaw (0.48 ± 0.04 mg m-2  hr-1 ). The mean duration of autumn freeze (58.94 ± 26.39 days) is significantly longer than that of spring thaw (20.94 ± 7.79 days), which predominates the much higher cumulative CH4 emission during autumn freeze (1,212.31 ± 280.39 mg m-2  year-1 ) than that during spring thaw (307.39 ± 46.11 mg m-2  year-1 ). Near-surface soil temperatures cannot completely reflect the freeze-thaw processes in deeper soil layers and appears to have a hysteresis effect on CH4 emissions from early spring thaw to late autumn freeze. Therefore, it is necessary to consider commonalities and differences in CH4 emissions during spring thaw versus autumn freeze to accurately estimate CH4 source from tundra ecosystems for evaluating carbon-climate feedback in Arctic.

In Situ pH Measurements of Individual Levitated Microdroplets Using Aerosol Optical Tweezers.

The pH of microscale reaction environments controls numerous physicochemical processes, requiring a real-time pH microprobe. We present highly accurate real-time pH measurements of microdroplets using aerosol optical tweezers (AOT) and analysis of the whispering gallery modes (WGMs) contained in the cavity-enhanced Raman spectra. Uncertainties ranging from ±0.03 to 0.06 in pH for picoliter droplets are obtained through averaging Raman frames acquired at 0.5 Hz over 3.3 min. The high accuracy in pH determination is achieved by combining two independent measurements uniquely provided by the AOT approach: the anion concentration ratio from the spontaneous Raman spectra, and the total solute concentration from the refractive index retrieved from WGM analysis of the stimulated cavity-enhanced Raman spectra. pH can be determined over a range of -0.36 to 0.76 using the aqueous sodium bisulfate system. This technique enables direct measurements of pH-dependent chemical and physical changes experienced by individual microparticles and exploration of the role of pH in the chemical behavior of confined microenvironments.

Using Ionic Liquids To Study the Migration of Semivolatile Organic Vapors in Smog Chamber Experiments.

Atmospheric organic aerosols comprise complex mixtures of a myriad of compounds with a wide range of structures and volatilities. To understand the fate of atmospheric organic aerosols and their contribution to particulate matter pollution, we need to study the relative portion divided between semivolatile organic compounds (SVOCs) and low-volatility organic compounds (LVOCs). SVOCs can effectively migrate and exchange between aerosol populations and thus are more accessible for further reactions and removal processes, while LVOCs will essentially stay in the particle phase. Here, we introduce using ionic liquid droplets as novel sorbents for organic vapors in smog chamber experiments to study the transfer of constituents between aerosol populations and to separate SVOCs and LVOCs from chamber-produced secondary organic aerosols (SOAs). SOA was formed and condensed on the ammonium-sulfate seeds, and later ionic liquid droplets were introduced into the chamber. We show that there are considerable yields of both LVOCs and SVOCs produced from α-pinene ozonolysis, and the uptake of SVOCs into the ionic liquid increases as the amount of reacted α-pinene increases. We also show that the SVOCs absorbed into the ionic liquid re-evaporate more readily compared to SOA originally condensed on the ammonium-sulfate seeds. We are thus able to differentiate the semivolatile components that partition into the extremely polar ionic liquid aerosols from the demonstrably less volatile components also condensed on the ammonium-sulfate seeds. Combined with previous studies using other organic aerosols as solvents to probe SVOC transfer between aerosol populations, we provide a wide set of measurements to probe and constrain the physical and thermodynamic properties of chamber-produced SOA complex.

Mixing of secondary organic aerosols versus relative humidity.

Atmospheric aerosols exert a substantial influence on climate, ecosystems, visibility, and human health. Although secondary organic aerosols (SOA) dominate fine-particle mass, they comprise myriad compounds with uncertain sources, chemistry, and interactions. SOA formation involves absorption of vapors into particles, either because gas-phase chemistry produces low-volatility or semivolatile products that partition into particles or because more-volatile organics enter particles and react to form lower-volatility products. Thus, SOA formation involves both production of low-volatility compounds and their diffusion into particles. Most chemical transport models assume a single well-mixed phase of condensing organics and an instantaneous equilibrium between bulk gas and particle phases; however, direct observations constraining diffusion of semivolatile organics into particles containing SOA are scarce. Here we perform unique mixing experiments between SOA populations including semivolatile constituents using quantitative, single-particle mass spectrometry to probe any mass-transfer limitations in particles containing SOA. We show that, for several hours, particles containing SOA from toluene oxidation resist exchange of semivolatile constituents at low relative humidity (RH) but start to lose that resistance above 20% RH. Above 40% RH, the exchange of material remains constant up to 90% RH. We also show that dry particles containing SOA from α-pinene ozonolysis do not appear to resist exchange of semivolatile compounds. Our interpretation is that in-particle diffusion is not rate-limiting to mass transfer in these systems above 40% RH. To the extent that these systems are representative of ambient SOA, we conclude that diffusion limitations are likely not common under typical ambient boundary layer conditions.

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.

Production of N2O5 and ClNO2 through Nocturnal Processing of Biomass-Burning Aerosol.

Biomass burning is a source of both particulate chloride and nitrogen oxides, two important precursors for the formation of nitryl chloride (ClNO2), a source of atmospheric oxidants that is poorly prescribed in atmospheric models. We investigated the ability of biomass burning to produce N2O5(g) and ClNO2(g) through nocturnal chemistry using authentic biomass-burning emissions in a smog chamber. There was a positive relationship between the amount of ClNO2 formed and the total amount of particulate chloride emitted and with the chloride fraction of nonrefractory particle mass. In every fuel tested, dinitrogen pentoxide (N2O5) formed quickly, following the addition of ozone to the smoke aerosol, and ClNO2(g) production promptly followed. At atmospherically relevant relative humidities, the particulate chloride in the biomass-burning aerosol was rapidly but incompletely displaced, likely by the nitric acid produced largely by the heterogeneous uptake of N2O5(g). Despite this chloride acid displacement, the biomass-burning aerosol still converted on the order of 10% of reacted N2O5(g) into ClNO2(g). These experiments directly confirm that biomass burning is a potentially significant source of atmospheric N2O5 and ClNO2 to the atmosphere.

Spatial Variability of Sources and Mixing State of Atmospheric Particles in a Metropolitan Area.

Characterizing intracity variations of atmospheric particulate matter has mostly relied on fixed-site monitoring and quantifying variability in terms of different bulk aerosol species. In this study, we performed ground-based mobile measurements using a single-particle mass spectrometer to study spatial patterns of source-specific particles and the evolution of particle mixing state in 21 areas in the metropolitan area of Pittsburgh, PA. We selected sampling areas based on traffic density and restaurant density with each area ranging from 0.2 to 2 km2. Organics dominate particle composition in all of the areas we sampled while the sources of organics differ. The contribution of particles from traffic and restaurant cooking varies greatly on the neighborhood scale. We also investigate how primary and aged components in particles mix across the urban scale. Lastly we quantify and map the particle mixing state for all areas we sampled and discuss the overall pattern of mixing state evolution and its implications. We find that in the upwind and downwind of the urban areas, particles are more internally mixed while in the city center, particle mixing state shows large spatial heterogeneity that is mostly driven by emissions. This study is to our knowledge, the first study to perform fine spatial scale mapping of particle mixing state using ground-based mobile measurement and single-particle mass spectrometry.

Emulsified and Liquid-Liquid Phase-Separated States of α-Pinene Secondary Organic Aerosol Determined Using Aerosol Optical Tweezers.

We demonstrate the first capture and analysis of secondary organic aerosol (SOA) on a droplet suspended in an aerosol optical tweezers (AOT). We examine three initial chemical systems of aqueous NaCl, aqueous glycerol, and squalane at ∼75% relative humidity. For each system we added α-pinene SOA-generated directly in the AOT chamber-to the trapped droplet. The resulting morphology was always observed to be a core of the original droplet phase surrounded by a shell of the added SOA. We also observed a stable emulsion of SOA particles when added to an aqueous NaCl core phase, in addition to the shell of SOA. The persistence of the emulsified SOA particles suspended in the aqueous core suggests that this metastable state may persist for a significant fraction of the aerosol lifecycle for mixed SOA/aqueous particle systems. We conclude that the α-pinene SOA shell creates no major diffusion limitations for water, glycerol, and squalane core phases under humid conditions. These experimental results support the current prompt-partitioning framework used to describe organic aerosol in most atmospheric chemical transport models and highlight the prominence of core-shell morphologies for SOA on a range of core chemical phases.

Bringing the ocean into the laboratory to probe the chemical complexity of sea spray aerosol.

The production, size, and chemical composition of sea spray aerosol (SSA) particles strongly depend on seawater chemistry, which is controlled by physical, chemical, and biological processes. Despite decades of studies in marine environments, a direct relationship has yet to be established between ocean biology and the physicochemical properties of SSA. The ability to establish such relationships is hindered by the fact that SSA measurements are typically dominated by overwhelming background aerosol concentrations even in remote marine environments. Herein, we describe a newly developed approach for reproducing the chemical complexity of SSA in a laboratory setting, comprising a unique ocean-atmosphere facility equipped with actual breaking waves. A mesocosm experiment was performed in natural seawater, using controlled phytoplankton and heterotrophic bacteria concentrations, which showed SSA size and chemical mixing state are acutely sensitive to the aerosol production mechanism, as well as to the type of biological species present. The largest reduction in the hygroscopicity of SSA occurred as heterotrophic bacteria concentrations increased, whereas phytoplankton and chlorophyll-a concentrations decreased, directly corresponding to a change in mixing state in the smallest (60-180 nm) size range. Using this newly developed approach to generate realistic SSA, systematic studies can now be performed to advance our fundamental understanding of the impact of ocean biology on SSA chemical mixing state, heterogeneous reactivity, and the resulting climate-relevant properties.

Influence of functional groups on organic aerosol cloud condensation nucleus activity.

Organic aerosols in the atmosphere are composed of a wide variety of species, reflecting the multitude of sources and growth processes of these particles. Especially challenging is predicting how these particles act as cloud condensation nuclei (CCN). Previous studies have characterized the CCN efficiency for organic compounds in terms of a hygroscopicity parameter, κ. Here we extend these studies by systematically testing the influence of the number and location of molecular functional groups on the hygroscopicity of organic aerosols. Organic compounds synthesized via gas-phase and liquid-phase reactions were characterized by high-performance liquid chromatography coupled with scanning flow CCN analysis and thermal desorption particle beam mass spectrometry. These experiments quantified changes in κ with the addition of one or more functional groups to otherwise similar molecules. The increase in κ per group decreased in the following order: hydroxyl ≫ carboxyl > hydroperoxide > nitrate ≫ methylene (where nitrate and methylene produced negative effects, and hydroperoxide and nitrate groups produced the smallest absolute effects). Our results contribute to a mechanistic understanding of chemical aging and will help guide input and parametrization choices in models relying on simplified treatments such as the atomic oxygen:carbon ratio to predict the evolution of organic aerosol hygroscopicity.

Evaluation of iodide chemical ionization mass spectrometry for gas and aerosol-phase per- and polyfluoroalkyl substances (PFAS) analysis.

Per- and polyfluoroalkyl substances (PFAS) are a class of ultra-persistent anthropogenic contaminants. PFAS are ubiquitous in environmental and built systems, but very few online methods exist for their characterization in atmospheric gases and aerosols. Iodide time-of-flight chemical ionization mass spectrometry (iodide-ToF-CIMS) is a promising technology for online characterization of PFAS in the atmosphere. Previous work using iodide-ToF-CIMS was successful in measuring gas-phase perfluoroalkyl carboxylic acids and fluorotelomer alcohols, but those are just two of the myriad classes of PFAS that are atmospherically relevant. Therefore, our first objective was to test other sample introduction methods coupled to iodide-TOF-CIMS to evaluate its ability to measure a wider suite of PFAS in both gas and aerosol phases. Using a variety of sample introduction techniques, we successfully measured gas-phase fluorotelomer alcohols (FTOHs), gas and aerosol-phase perfluoroalkyl carboxylic acids (PFCAs), and aerosol-phase perfluoroalkyl sulfonic acids and polyfluoroalkyl phosphoric acid diesters (PFSAs and diPAPs). We also determined iodide-ToF-CIMS response factors for these compounds by introducing known quantities using a Filter Inlet for Gases and AEROsols (FIGAERO). These response factors ranged from 400 to 6 × 104 ions per nanogram, demonstrating low limits of detection. Furthermore, PFAS are a poorly understood diverse class of molecules that exhibit unusual and often unexpected physicochemical properties due to their highly fluorinated nature. Since detection of PFAS with iodide-ToF-CIMS relies on the analyte molecule to either undergo proton transfer or adduct formation with iodide, understanding PFAS behavior during chemical ionization gives rise to a more fundamental understanding of these compounds. Through voltage scanning experiments and DFT calculations, we found that PFCAs and FTOHs readily form iodide adducts, while PFSAs and diPAPs preferentially undergo proton transfer to iodide. Generally, binding energy increased with increasing linear chain length, and PFCAs had stronger binding than FTOHs. Overall, our results suggest that iodide-ToF-CIMS can be used to measure even nonvolatile PFAS such as PFSAs and diPAPs in the aerosol phase in a semi-continuous online fashion.

Nontarget analysis and fluorine atom balances of transformation products from UV/sulfite degradation of perfluoroalkyl contaminants.

Per- and polyfluoroalkyl substances (PFAS) are a class of thousands of highly fluorinated, anthropogenic compounds that are used in a wide variety of consumer applications. Due to their widespread use and high persistence, PFAS are ubiquitous in drinking water, which is of concern due to the threats these compounds pose to human health. Reduction via the hydrated electron is a promising technology for PFAS remediation and has been well-studied. However, since previous work rarely reports fluorine atom balances and often relies on suspect screening, some transformation products are likely unaccounted for. Therefore, we performed non-target analysis using high-resolution mass spectrometry on solutions of perfluorooctanesulfonate (PFOS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), and 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoate (GenX) that had been treated with UV/sulfite to produce hydrated electrons. We determined fluorine atom balances for all compounds studied, finding high fluorine atom balances for PFOS and PFBS. PFOA and GenX had lower overall fluorine atom balances, likely due to the production of volatile or very polar transformation products that were not measured by our methods. Transformation products identified by our analysis were consistent with literature, with a few exceptions. Namely, shorter-chain perfluorosulfonates (PFSA) and their H/F substituted counterparts were also detected from PFOS. This is an unexpected result based on literature, as no documented pathway exists for the formation of shorter-chain PFSA during UV/sulfite treatment. Furthermore, the nontarget approach we employed allowed for identification of novel, unsaturated products from the hydrated electron treatment of perfluorooctanesulfonate (PFOS) that warrant further investigation.

Aging-associated augmentation of gut microbiome virulence capability drives sepsis severity.

Prior research has focused on host factors as mediators of exaggerated sepsis-associated morbidity and mortality in older adults. This focus on the host, however, has failed to identify therapies that improve sepsis outcomes in the elderly. We hypothesized that the increased susceptibility of the aging population to sepsis is not only a function of the host, but also reflects longevity-associated changes in the virulence of gut pathobionts. We utilized two complementary models of gut microbiota-induced experimental sepsis to establish the aged gut microbiome as a key pathophysiologic driver of heightened disease severity. Further murine and human investigations into these polymicrobial bacterial communities demonstrated that age was associated with only subtle shifts in ecological composition, but an overabundance of genomic virulence factors that have functional consequence on host immune evasion. One Sentence Summary: The severity of sepsis in the aged host is in part mediated by longevity-associated increases in gut microbial virulence.

Aging-Associated Augmentation of Gut Microbiome Virulence Capability Drives Sepsis Severity.

Prior research has focused on host factors as mediators of exaggerated sepsis-associated morbidity and mortality in older adults. This focus on the host, however, has failed to identify therapies that improve sepsis outcomes in the elderly. We hypothesized that the increased susceptibility of the aging population to sepsis is not only a function of the host but also reflects longevity-associated changes in the virulence of gut pathobionts. We utilized two complementary models of gut microbiota-induced experimental sepsis to establish the aged gut microbiome as a key pathophysiologic driver of heightened disease severity. Further murine and human investigations into these polymicrobial bacterial communities demonstrated that age was associated with only subtle shifts in ecological composition but also an overabundance of genomic virulence factors that have functional consequence on host immune evasion. IMPORTANCE Older adults suffer more frequent and worse outcomes from sepsis, a critical illness secondary to infection. The reasons underlying this unique susceptibility are incompletely understood. Prior work in this area has focused on how the immune response changes with age. The current study, however, focuses instead on alterations in the community of bacteria that humans live with within their gut (i.e., the gut microbiome). The central concept of this paper is that the bacteria in our gut evolve along with the host and "age," making them more efficient at causing sepsis.

Volcanic ash ice nucleation activity is variably reduced by aging in water and sulfuric acid: the effects of leaching, dissolution, and precipitation.

Volcanic ash nucleates ice when immersed in supercooled water droplets, giving it the potential to influence weather and climate from local to global scales. This ice nucleation activity (INA) is likely derived from a subset of the crystalline mineral phases in the ash. The INA of other mineral-based dusts can change when exposed to various gaseous and aqueous chemical species, many of which also interact with volcanic ash in the eruption plume and atmosphere. However, the effects of aqueous chemical aging on the INA of volcanic ash have not been explored. We show that the INA of two mineralogically distinct ash samples from Fuego and Astroni volcanoes is variably reduced following immersion in water or aqueous sulfuric acid for minutes to days. Aging in water decreases the INA of both ash samples by up to two orders of magnitude, possibly due to a reduction in surface crystallinity and cation availability accompanying leaching. Aging in sulfuric acid leads to minimal loss of INA for Fuego ash, which is proposed to reflect a quasi-equilibrium between leaching that removes ice-active sites and dissolution that reveals or creates new sites on the pyroxene phases present. Conversely, exposure to sulfuric acid reduces the INA of Astroni ash by one to two orders of magnitude, potentially through selective dissolution of ice-active sites associated with surface microtextures on some K-feldspar phases. Analysis of dissolved element concentrations in the aged ash leachates shows supersaturation of certain mineral species which could have precipitated and altered the INA of the ash. These results highlight the key role that leaching, dissolution, and precipitation likely play in the aqueous aging of volcanic ash with respect to its INA. Finally, we discuss the implications for understanding the nature and reactivity of ice-active sites on volcanic ash and its role in influencing cloud properties in the atmosphere.

Preventing spread of aerosolized infectious particles during medical procedures: A lab-based analysis of an inexpensive plastic enclosure.

Severe viral respiratory diseases, such as SARS-CoV-2, are transmitted through aerosol particles produced by coughing, talking, and breathing. Medical procedures including tracheal intubation, extubation, dental work, and any procedure involving close contact with a patient's airways can increase exposure to infectious aerosol particles. This presents a significant risk for viral exposure of nearby healthcare workers during and following patient care. Previous studies have examined the effectiveness of plastic enclosures for trapping aerosol particles and protecting health-care workers. However, many of these enclosures are expensive or are burdensome for healthcare workers to work with. In this study, a low-cost plastic enclosure was designed to reduce aerosol spread and viral transmission during medical procedures, while also alleviating issues found in the design and use of other medical enclosures to contain aerosols. This enclosure is fabricated from clear polycarbonate for maximum visibility. A large single-side cutout provides health care providers with ease of access to the patient with a separate cutout for equipment access. A survey of medical providers in a local hospital network demonstrated their approval of the enclosure's ease of use and design. The enclosure with appropriate plastic covers reduced total escaped particle number concentrations (diameter > 0.01 µm) by over 93% at 8 cm away from all openings. Concentration decay experiments indicated that the enclosure without active suction should be left on the patient for 15-20 minutes following a tracheal manipulation to allow sufficient time for >90% of aerosol particles to settle upon interior surfaces. This decreases to 5 minutes when 30 LPM suction is applied. This enclosure is an inexpensive, easily implemented additional layer of protection that can be used to help contain infectious or otherwise potentially hazardous aerosol particles while providing access into the enclosure.