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The hydrolysis rates of many organic chemicals are accelerated under alkaline conditions by the presence of hydroxide (HO - ), which is typically assumed to be the predominant species contributing to base-catalyzed hydrolysis in both natural waters and laboratory buffers used in standard protocols. In this study, we demonstrated that weak bases (e.g., carbonates and phosphates) are able to catalyze the hydrolysis of the proherbicide isoxaflutole, an emerging contaminant of concern in water resources, under conditions relevant to both natural waters and laboratory protocols. Second-order rate constants for isoxaflutole hydrolysis catalyzed by individual bases were correlated with the p K a , resulting in hydrolysis rates predicted in natural waters overestimated by 5- to 30-fold from pH 7.0 to 8.5. In comparison, our corrected rate constants accurately predicted isoxaflutole hydrolysis measured in natural waters within a factor of 5. While isoxaflutole hydrolysis in surface water remains predominantly catalyzed by HO - following standard assumptions, carbonate species (particularly bicarbonate) are predicted to drive the reaction in as many as 83% of groundwater systems.- following standard assumptions, carbonate species (particularly bicarbonate) are predicted to drive the reaction in as many as 83% of groundwater systems.

Supercritical (sc) CO 2 in geologic carbon sequestration (GCS) can chemically and mechanically deteriorate wellbore cement, raising concerns for long-term operations. In contrast to the conventional view of "sulfate attack" on cement, we found that adding 0.15 M sulfate to the acidic brine can significantly reduce the impact of scCO 2 attack on Portland cement, resulting in stronger cement than that found in a sulfate-free system. Scanning electron microscopy revealed a decreased total attack depth in reacted cement in the presence of sulfate. With a newly defined minimum porosity term in reactive transport modeling, our model suggests that sulfate caused CaCO 3 to fill more nanopore spaces in the cement. Small angle X-ray scattering experiments also showed that sulfate can decrease the pore sizes of the carbonate layer. The results suggest that the interactions between sulfate and cement can generate a less porous CaCO 3 layer, which better resists acidic brine. Using this mechanism as a proof-of-concept, we tested the incorporation of sodium sulfate into Portland cement and synthesized new cement composites that show stronger resistance against scCO 2 attacks. These newly discovered interfacial interactions between CaCO 3 and sulfate provide new insights into engineering mechanically strong and green materials for safer GCS.

Lead(IV) oxide (PbO 2 ) is an important component of the scale in many lead pipes used for water supply. Promoting conditions that maintain its stability could be an effective method for limiting lead release. In this study, we applied a method that combined electrochemical and free chlorine conditioning to form PbO 2 scales on coupons. Lead coupons were then used to investigate the impacts of water stagnation time and residual free chlorine on PbO 2 stability. Free chlorine depletion and associated lead release were investigated from 30 min to 5 days for different initial free chlorine concentrations (0.5-3.0 mg/L as Cl 2 ). There was a lag time of up to 24 h between free chlorine depletion and observed lead increases. With daily readjustment of free chlorine to 0.2 mg/L or higher, the stability of the PbO 2 scale on the lead coupon was maintained and dissolved lead remained consistently below 10 μg/L. This study provides information on key factors affecting reductive dissolution of PbO 2 present in lead scales. It bridges the theoretical threshold free chlorine to maintain PbO 2 stability with experimental results and provides implications for actual water quality monitoring and household drinking water use.

The development of genetically engineered microbes (GEMs) has resulted in an urgent need to control their persistence in the environment. The use of biocontainment such as kill switches is a critical approach to prevent the unintended proliferation of GEMs; however, the effectiveness of kill switches─reported as escape rates, i.e., the ratio of the number of viable microbes when the kill switch is triggered relative to the number when it is not triggered─is typically assessed under laboratory conditions that do not resemble environmental conditions under which biocontainment must perform. In this study, we discovered that the escape rate of an Escherichia coli GEM biocontained with a CRISPR-based kill switch triggered by anhydrotetracycline (aTc) increased by 3-4 orders of magnitude when deployed in natural surface waters as compared to rich laboratory media. We identified that environmental conditions (e.g., pH, nutrient levels) may contribute to elevated escape rates in multiple ways, including by altering the chemical speciation of the kill switch trigger to reduce its uptake and providing limited nutrients required for the kill switch to function. Our study demonstrated that conditions in the intended environment must be considered in order to design effective GEM biocontainment strategies.

Cannabis smoke is a complex aerosol mixture, featuring characteristic monoterpenes and sesquiterpenes which are susceptible to reaction with ozone and other oxidants. These reactions form less-volatile species which can contribute to secondary organic aerosol (SOA) and ultrafine particle (UFP) formation. In this work, the reaction of ozone with cannabis smoke was observed in an environmental chamber. Particle size distribution, and gas-phase and particle-phase composition were monitored in real time. The diameter of primary particles ranged from 10 -1 to 1 μm. Ultrafine particle formation occurred when cannabis smoke was exposed to ozone levels greater than 10 ppb, over the entire observed primary particle concentration range (1030-4580 μg m -3 ). Gas-phase measurements indicate that monoterpene and sesquiterpene levels decayed rapidly upon ozone exposure, while oxygen-containing species were formed during oxidation. On the other hand, measurements of particle composition showed an increase in nitrogen-containing species during oxidation. Although ozone was the only oxidant added to cannabis smoke in the chamber, it is believed that the OH radical plays an important role in the oxidation mechanism, where OH results from the reaction of ozone with terpenes and sesquiterpenes. Overall, smoking cannabis in ozone-rich environments, both indoors and outdoors, will likely lead to UFP formation.

Wildfires are an increasing source of emissions into the air, with health effects modulated by the abundance and toxicity of individual species. In this work, we estimate reactive organic compounds (ROC) in western U.S. wildland forest fire smoke using a combination of observations from the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign and predictions from the Community Multiscale Air Quality (CMAQ) model. Standard emission inventory methods capture 40-45% of the estimated ROC mass emitted, with estimates of primary organic aerosol particularly low (5-8×). Downwind, gas-phase species abundances in molar units reflect the production of fragmentation products such as formaldehyde and methanol. Mass-based units emphasize larger compounds, which tend to be unidentified at an individual species level, are less volatile, and are typically not measured in the gas phase. Fire emissions are estimated to total 1250 ± 60 g·C of ROC per kg·C of CO, implying as much carbon is emitted as ROC as is emitted as CO. Particulate ROC has the potential to dominate the cancer and noncancer risk of long-term exposure to inhaled smoke, and better constraining these estimates will require information on the toxicity of particulate ROC from forest fires.

Dicamba is a semivolatile herbicide that has caused widespread unintentional damage to vegetation due to its volatilization from genetically engineered dicamba-tolerant crops. Strategies to reduce dicamba volatilization rely on the use of formulations containing amines, which deprotonate dicamba to generate a nonvolatile anion in aqueous solution. Dicamba volatilization in the field is also expected to occur after aqueous spray droplets dry to produce a residue; however, dicamba speciation in this phase is poorly understood. We applied Fourier transform infrared (FTIR) spectroscopy to evaluate dicamba protonation state in dried dicamba-amine residues. We first demonstrated that commercially relevant amines such as diglycolamine (DGA) and n , n -bis(3-aminopropyl)methylamine (BAPMA) fully deprotonated dicamba when applied at an equimolar molar ratio, while dimethylamine (DMA) allowed neutral dicamba to remain detectable, which corresponded to greater dicamba volatilization. Expanding the amines tested, we determined that dicamba speciation in the residues was unrelated to solution-phase amine p K a -metolachlor registered for use alongside dicamba) to investigate dicamba speciation in a more complex chemical environment encountered in field applications.S -metolachlor registered for use alongside dicamba) to investigate dicamba speciation in a more complex chemical environment encountered in field applications.

Plasma has been proposed as an alternative strategy to treat organic contaminants in brines. Chemical degradation in these systems is expected to be partially driven by halogen oxidants, which have been detected in halide-containing solutions exposed to plasma. In this study, we characterized specific mechanisms involving the formation and reactions of halogen oxidants during plasma treatment. We first demonstrated that addition of halides accelerated the degradation of a probe compound known to react quickly with halogen oxidants (i.e., para -hydroxybenzoate) but did not affect the degradation of a less reactive probe compound (i.e., benzoate). This effect was attributed to the degradation of para -hydroxybenzoate by hypohalous acids, which were produced via a mechanism involving halogen radicals as intermediates. We applied this mechanistic insight to investigate the impact of constituents in brines on reactions driven by halogen oxidants during plasma treatment. Bromide, which is expected to occur alongside chloride in brines, was required to enable halogen oxidant formation, consistent with the generation of halogen radicals from the oxidation of halides by hydroxyl radical. Other constituents typically present in brines (i.e., carbonates, organic matter) slowed the degradation of organic compounds, consistent with their ability to scavenge species involved during plasma treatment.

The dynamics of trace metals at mineral surfaces influence their fate and bioaccessibility in the environment. Trace metals on iron (oxyhydr)oxide surfaces display adsorption-desorption hysteresis, suggesting entrapment after aging. However, desorption experiments may perturb the coordination environment of adsorbed metals, the distribution of labile Fe(III), and mineral aggregation properties, influencing the interpretation of labile metal fractions. In this study, we investigated irreversible binding of nickel, zinc, and cadmium to goethite after aging times of 2-120 days using isotope exchange. Dissolved and adsorbed metal pools exchange rapidly, with half times <90 min, but all metals display a solid-associated fraction inaccessible to isotope exchange. The size of this nonlabile pool is the largest for nickel, with the smallest ionic radius, and the smallest for cadmium, with the largest ionic radius. Spectroscopy and extractions suggest that the irreversibly bound metals are incorporated in the goethite structure. Rapid exchange of labile solid-associated metals with solution demonstrates that adsorbed metals can sustain the dissolved pool in response to biological uptake or fluid flow. Trace metal fractions that irreversibly bind following adsorption provide a contaminant sequestration pathway, limit the availability of micronutrients, and record metal isotope signatures of environmental processes.

The herbicide isoxaflutole has the potential to contaminate drinking water directly, as well as upon hydrolyzing to its active form diketonitrile. Diketonitrile also may impact water quality by acting as a precursor for dichloroacetonitrile (DCAN), which is an unregulated but highly toxic disinfection byproduct (DBP). In this study, we investigated the reaction of diketonitrile with free chlorine and chloramine to form DCAN. We found that diketonitrile reacts with free chlorine within seconds but reacts with chloramine on the time scale of hours to days. In the presence of both oxidants, DCAN was generated at yields up to 100%. Diketonitrile reacted fastest with chlorine at circumneutral pH, which was consistent with base-catalyzed halogenation involving the enolate form of diketonitrile present at alkaline pH and electrophilic hypochlorous acid, which decreases in abundance above its p K (7.5). In contrast, we found that diketonitrile reacts faster with chloramine as pH values decreased, consistent with an attack on the enolate by electrophilic protonated monochloramine that increases in abundance at acidic pH approaching its p a (1.6). Our results indicate that increasing isoxaflutole use, particularly in light of the recent release of genetically modified isoxaflutole-tolerant crops, could result in greater occurrences of a high-yield DCAN precursor during disinfection.K a (1.6). Our results indicate that increasing isoxaflutole use, particularly in light of the recent release of genetically modified isoxaflutole-tolerant crops, could result in greater occurrences of a high-yield DCAN precursor during disinfection.

Fine particulate matter (PM 2.5 ) chemical composition has strong and diverse impacts on the planetary environment, climate, and health. These effects are still not well understood due to limited surface observations and uncertainties in chemical model simulations. We developed a four-dimensional spatiotemporal deep forest (4D-STDF) model to estimate daily PM 2.5 chemical composition at a spatial resolution of 1 km in China since 2000 by integrating measurements of PM 2.5 species from a high-density observation network, satellite PM 2.5 retrievals, atmospheric reanalyses, and model simulations. Cross-validation results illustrate the reliability of sulfate (SO 4 2- ), nitrate (NO 3 - ), ammonium (NH 4 + ), and chloride (Cl - ) estimates, with high coefficients of determination (CV-R 2 ) with ground-based observations of 0.74, 0.75, 0.71, and 0.66, and average root-mean-square errors (RMSE) of 6.0, 6.6, 4.3, and 2.3 μg/m 3 , respectively. The three components of secondary inorganic aerosols (SIAs) account for 21% (SO 4 mass in eastern China; we observed significant reductions in the mass of inorganic components by 40-43% between 2013 and 2020, slowing down since 2018. Comparatively, the ratio of SIA to PM 2- increased by 7% across eastern China except in Beijing and nearby areas, accelerating in recent years. SO 3 has been the dominant SIA component in eastern China, although it was surpassed by NO - in some areas, e.g., Beijing-Tianjin-Hebei region since 2016. SIA, accounting for nearly half (∼46%) of the PM 4 mass, drove the explosive formation of winter haze episodes in the North China Plain. A sharp decline in SIA concentrations and an increase in SIA-to-PM + ) of the total PM 2.5 mass in eastern China; we observed significant reductions in the mass of inorganic components by 40-43% between 2013 and 2020, slowing down since 2018. Comparatively, the ratio of SIA to PM 2.5 increased by 7% across eastern China except in Beijing and nearby areas, accelerating in recent years. SO 4 2- has been the dominant SIA component in eastern China, although it was surpassed by NO 3 - in some areas, e.g., Beijing-Tianjin-Hebei region since 2016. SIA, accounting for nearly half (∼46%) of the PM 2.5 mass, drove the explosive formation of winter haze episodes in the North China Plain. A sharp decline in SIA concentrations and an increase in SIA-to-PM 2.5 ratios during the COVID-19 lockdown were also revealed, reflecting the enhanced atmospheric oxidation capacity and formation of secondary particles.

The persistence of RNA in environmental systems is an important parameter for emerging applications, including ecological surveys, wastewater-based epidemiology, and RNA interference biopesticides. RNA persistence is controlled by its rate of biodegradation, particularly by extracellular enzymes, although the specific factors determining this rate have not been characterized. Due to prior work suggesting that nucleic acids-specifically DNA-interact with dissolved organic matter (DOM), we hypothesized that DOM may bind RNA and impede its biodegradation in natural systems. We first adapted a technique previously used to assess RNA-protein binding to differentiate RNA that is bound at all sites by DOM from RNA that is unbound or partially bound by DOM. Results from this technique suggested that humic acids bound RNA more extensively than fulvic acids. At concentrations of 8-10 mg C /L, humic acids were also found to be more effective than fulvic acids at suppressing enzymatic degradation of RNA. In surface water and soil extract containing DOM, RNA degradation was suppressed by 39-46% relative to pH-adjusted controls. Due to the ability of DOM to both bind and suppress the enzymatic degradation of RNA, RNA biodegradation may be slowed in environmental systems with high DOM concentrations, which may increase its persistence.

Wastewater-based testing (WBT) for SARS-CoV-2 has rapidly expanded over the past three years due to its ability to provide a comprehensive measurement of disease prevalence independent of clinical testing. The development and simultaneous application of WBT measured biomarkers for research activities and for the pursuit of public health goals, both areas with well-established ethical frameworks. Currently, WBT practitioners do not employ a standardized ethical review process, introducing the potential for adverse outcomes for WBT professionals and community members. To address this deficiency, an interdisciplinary workshop developed a framework for a structured ethical review of WBT. The workshop employed a consensus approach to create this framework as a set of 11 questions derived from primarily public health guidance. This study retrospectively applied these questions to SARS-CoV-2 monitoring programs covering the emergent phase of the pandemic (3/2020-2/2022 ( n = 53)). Of note, 43% of answers highlight a lack of reported information to assess. Therefore, a systematic framework would at a minimum structure the communication of ethical considerations for applications of WBT. Consistent application of an ethical review will also assist in developing a practice of updating approaches and techniques to reflect the concerns held by both those practicing and those being monitored by WBT supported programs.

Because of its favorable thermodynamics and fast kinetics, heterogeneous solid nucleation on membranes triggers early-stage mineral scaling. Iron (hydr)oxide, a typical membrane scale, initially forms as nanoparticles that interact with surface functional groups on membranes, but these nanoscale phenomena are difficult to observe in real time. In this study, we utilized in situ grazing incidence small angle X-ray scattering and ex situ atomic force microscopy to examine the heterogeneous nucleation of iron (hydr)oxide on surface functional groups commonly used in membranes, including hydroxyl (OH), carboxyl (COOH), and fluoro (F) groups. We found that, compared to nucleation on hydrophilic OH- and COOH-surfaces, the high hydrophobicity of an F-modified surface significantly reduced the extents of both heterogeneously and homogeneously formed iron (hydr)oxide nucleation. Moreover, on the OH-surface, the high functional group density of 0.76 nmol/cm 2 caused faster heterogeneous nucleation than that on a COOH-surface, with a density of 0.28 ± 0.04 nmol/cm 2 . The F-surface also had the highest heterogeneous nucleation energy barrier (26 ± 0.6 kJ/mol), followed by COOH- (23 ± 0.8 kJ/mol) and OH- (20 ± 0.9 kJ/mol) surfaces. The kinetic and thermodynamic information provided here will help us better predict the rates and extents of early-stage scaling of iron (hydr)oxide nanoparticles in membrane processes.

Fine particulate matter (PM 2.5 ) exposure is a leading mortality risk factor in India and the surrounding region of South Asia. This study evaluates the contribution of emission sectors and fuels to PM 2.5 mass for 29 states in India and 6 surrounding countries (Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka, and Myanmar) by combining source-specific emission estimates, stretched grid simulations from a chemical transport model, high resolution hybrid PM 2.5 , and disease-specific mortality estimates. We find that 1.02 (95% Confidence Interval (CI): 0.78-1.26) million deaths in South Asia attributable to ambient PM 2.5 in 2019 were primarily from three leading sectors: residential combustion (28%), industry (15%), and power generation (12%). Solid biofuel is the leading combustible fuel contributing to the PM 2.5 -attributable mortality (31%), followed by coal (17%), and oil and gas (14%). State-level analyses reveal higher residential combustion contributions (35%-39%) in states (Delhi, Uttar-Pradesh, Haryana) with high ambient PM 2.5 (>95 μg/m 3 ). The combined mortality burden associated with residential combustion (ambient) and household air pollution (HAP) in India is 0.72 million (95% CI:0.54-0.89) (68% attributable to HAP, 32% attributable to residential combustion). Our results illustrate the potential to reduce PM 2.5 mass and improve population health by reducing emissions from traditional energy sources across multiple sectors in South Asia.

Phosphorus (P) recovery from biosolids can play an important role in a circular economy. Herein, an electrochemical phosphorus recovery cell (EPRC) was proposed and examined to recover P from municipal whole digestate via simultaneous leaching and precipitation. The anode of the EPRC released P as aqueous PO 4 3- . When the leached P solution was treated in the cathode, native metals including Ca and Fe facilitated electrochemically mediated PO -2 -P precipitation (EMP) and precipitated ∼99% of the leached P in the cathode chamber. Around 54.3-78.7% of total P existed in two harvestable forms: suspended solids in the cathode effluent and immobilized P in the cathode chamber. The solid products contained 28.42-33.51% of P 4 3- , comparable to the high-grade phosphate rock. Higher current densities reduced cathode scaling and resulted in a lower content of heavy metals in the solid products. An acidic solution was reused three times and effectively maintained cathode performance during a 42-cycle operation, achieving a consistent P recovery efficiency of nearly 80%. Those results have demonstrated the feasibility of the EPRC for recovering P from P-rich solid wastes.2 O 5 , comparable to the high-grade phosphate rock. Higher current densities reduced cathode scaling and resulted in a lower content of heavy metals in the solid products. An acidic solution was reused three times and effectively maintained cathode performance during a 42-cycle operation, achieving a consistent P recovery efficiency of nearly 80%. Those results have demonstrated the feasibility of the EPRC for recovering P from P-rich solid wastes.

As an essential biomolecule for life, RNA is ubiquitous across environmental systems where it plays a central role in biogeochemical processes and emerging technologies. The persistence of RNA in soils and sediments is thought to be limited by enzymatic or microbial degradation, which occurs on timescales that are orders of magnitude faster than known abiotic pathways. Herein, we unveil a previously unreported abiotic pathway by which RNA rapidly hydrolyzes on the timescale of hours upon adsorption to iron (oxyhydr)oxide minerals such as goethite (α-FeOOH). The hydrolysis products were consistent with iron present in the minerals acting as a Lewis acid to accelerate sequence-independent hydrolysis of phosphodiester bonds comprising the RNA backbone. In contrast to acid- or base-catalyzed RNA hydrolysis in solution, mineral-catalyzed hydrolysis was fastest at circumneutral pH, which allowed for both sufficient RNA adsorption and hydroxide concentration. In addition to goethite, we observed that RNA hydrolysis was also catalyzed by hematite (α-Fe 2 O 3 ) but not by aluminum-containing minerals (e.g., montmorillonite). Given the extensive adsorption of nucleic acids to environmental surfaces, we anticipate previously overlooked mineral-catalyzed hydrolysis of RNA may be prevalent particularly in iron-rich soils and sediments, which must be considered across biogeochemical applications of nucleic acid analysis in environmental systems.

High-resolution simulations are essential to resolve fine-scale air pollution patterns due to localized emissions, nonlinear chemical feedbacks, and complex meteorology. However, high-resolution global simulations of air quality remain rare, especially of the Global South. Here, we exploit recent developments to the GEOS-Chem model in its high-performance implementation to conduct 1-year simulations in 2015 at cubed-sphere C360 (∼25 km) and C48 (∼200 km) resolutions. We investigate the resolution dependence of population exposure and sectoral contributions to surface fine particulate matter (PM 2.5 ) and nitrogen dioxide (NO 2 ), focusing on understudied regions. Our results indicate pronounced spatial heterogeneity at high resolution (C360) with large global population-weighted normalized root-mean-square difference (PW-NRMSD) across resolutions for primary (62-126%) and secondary (26-35%) PM 2.5 species. Developing regions are more sensitive to spatial resolution resulting from sparse pollution hotspots, with PW-NRMSD for PM 2.5 in the Global South (33%), 1.3 times higher than globally. The PW-NRMSD for PM 2.5 for discrete southern cities (49%) is substantially higher than for more clustered northern cities (28%). We find that the relative order of sectoral contributions to population exposure depends on simulation resolution, with implications for location-specific air pollution control strategies.

Fe(II) clays are common across many environments, making them a potentially significant microbial substrate, yet clays are not well established as an electron donor. Therefore, we explored whether Fe(II)-smectite supports the growth of Sideroxydans lithotrophicus ES-1, a microaerophilic Fe(II)-oxidizing bacterium (FeOB), using synthesized trioctahedral Fe(II)-smectite and 2% oxygen. S. lithotrophicus grew substantially and can oxidize Fe(II)-smectite to a higher extent than abiotic oxidation, based on X-ray near-edge spectroscopy (XANES). Sequential extraction showed that edge-Fe(II) is oxidized before interior-Fe(II) in both biotic and abiotic experiments. The resulting Fe(III) remains in smectite, as secondary minerals were not detected in biotic and abiotic oxidation products by XANES and Mössbauer spectroscopy. To determine the genes involved, we compared S. lithotrophicus grown on smectite versus Fe(II)-citrate using reverse-transcription quantitative PCR and found that cyc2 genes were highly expressed on both substrates, while mtoA was upregulated on smectite. Proteomics confirmed that Mto proteins were only expressed on smectite, indicating that ES-1 uses the Mto pathway to access solid Fe(II). We integrate our results into a biochemical and mineralogical model of microbial smectite oxidation. This work increases the known substrates for FeOB growth and expands the mechanisms of Fe(II)-smectite alteration in the environment.

This study investigated antibiotic resistance gene (ARG) degradation kinetics in wastewaters during bench- and full-scale treatment with UV light and chlorine─with the latter maintained as free available chlorine (FAC) in low-ammonia wastewater and converted into monochloramine (NH 2 Cl) in high-ammonia wastewater. Twenty-three 142-1509 bp segments (i.e., amplicons) of seven ARGs ( blt , mecA , van A, tet (A), amp C, bla NDM , bla KPC ) and the 16S rRNA gene from antibiotic resistant bacteria (ARB) strains Bacillus subtilis , Staphylococcus aureus , Enterococcus faecium , Escherichia coli , Pseudomonas aeruginosa Cl were measured in phosphate buffer and used to expand and validate several recently developed approaches to predict DNA segment degradation rate constants based solely on their nucleotide contents, which were then applied to model ARG degradation during bench-scale treatment in buffer and wastewater matrixes. Kinetics of extracellular and intracellular ARG degradation by UV and FAC were well predicted up to ∼1-2-log Klebsiella pneumoniae were monitored as disinfection targets by qPCR. Rate constants for ARG and 16S rRNA gene amplicon degradation by UV, FAC, and NH 2 Cl yielded minimal degradation under all conditions (agreeing with predictions). ARB inactivation kinetics varied substantially across strains, with intracellular gene degradation lagging cell inactivation in each case. ARG degradation levels observed during full-scale disinfection at two wastewater treatment facilities were consistent with bench-scale measurements and predictions, where UV provided ∼1-log 10 elimination, although with decreasing accuracy at higher levels for intracellular genes, while NH 2 Cl yielded minimal degradation under all conditions (agreeing with predictions). ARB inactivation kinetics varied substantially across strains, with intracellular gene degradation lagging cell inactivation in each case. ARG degradation levels observed during full-scale disinfection at two wastewater treatment facilities were consistent with bench-scale measurements and predictions, where UV provided ∼1-log 10 ARG degradation, and chlorination of high-ammonia wastewater (dominated by NH 2 Cl) yielded minimal ARG degradation.

We investigated the influence of biomass burning (BURN), Diwali fireworks, and fog events on the ambient fine particulate matter (PM 2.5 ) oxidative potential (OP) during the postmonsoon (PMON) and winter season in Delhi, India. The real-time hourly averaged OP (based on a dithiothreitol assay) and PM 2.5 chemical composition were measured intermittently from October 2019 to January 2020. The peak extrinsic OP (OP v : normalized by the volume of air) was observed during the winter fog (WFOG) (5.23 ± 4.6 nmol·min -1 ·m -3 ), whereas the intrinsic OP (OP m ; normalized by the PM 2.5 mass) was the highest during the Diwali firework-influenced period (29.4 ± 18.48 pmol·min -1 ·μg -1 ). Source apportionment analysis using positive matrix factorization revealed that traffic + resuspended dust-related emissions (39%) and secondary sulfate + oxidized organic aerosols (38%) were driving the OP v during the PMON period, whereas BURN aerosols dominated (37%) the OP v during the WFOG period. Firework-related emissions became a significant contributor (∼32%) to the OP v during the Diwali period (4 day period from October 26 to 29), and its contribution peaked (72%) on the night of Diwali. Discerning the influence of seasonal and episodic sources on health-relevant properties of PM 2.5 , such as OP, could help better understand the causal relationships between PM 2.5 and health effects in India.

Amines are frequently included in formulations of the herbicides glyphosate, 2,4-D, and dicamba to increase herbicide solubility and reduce herbicide volatilization by producing herbicide-amine salts. Amines, which typically have higher vapor pressures than the corresponding herbicides, could potentially volatilize from these salts and enter the atmosphere, where they may impact atmospheric chemistry, human health, and climate. Amine volatilization from herbicide-amine salts may additionally contribute to volatilization of dicamba and 2,4-D. In this study, we established that amines applied in herbicide-amine salt formulations undergo extensive volatilization. Both dimethylamine and isopropylamine volatilized when aqueous salt solutions were dried to a residue at ∼20 °C, while lower-vapor pressure amines like diglycolamine and n , n - bis -(3-aminopropyl)methylamine did not. However, all four amines volatilized from salt residues at 40-80 °C. Because amine loss typically exceeded herbicide loss, we proposed that neutral amines dominated volatilization and that higher temperatures altered their protonation state and vapor pressure. Due to an estimated 4.0 Gg N/yr applied as amines to major U.S. crops, amine emissions from herbicide-amine salts may be important on regional scales. Further characterization of worldwide herbicide-amine use would enable this contribution to be compared to the 285 Gg N/yr of methylamines emitted globally.

The dynamics of Pb(II) at mineral surfaces affect its mobility in the environment. Pb(II) forms inner- and outer-sphere complexes on mineral surfaces, and this adsorbed pool often represents a large portion of the bioaccessible Pb in contaminated soils. To assess the lability of this potentially reactive adsorbed Pb(II) pool at metal oxide surfaces, we performed Pb(II) isotope exchange measurements between dissolved Pb(II) enriched in 207 Pb and natural isotopic abundance Pb(II) adsorbed to rutile at pH 5, 6, and 7. We find that ∼95% of the adsorbed lead is exchangeable. An initially fast exchange (<1 h) is followed by a slower exchange that occurs on a time scale of hours to days. Pb L III -edge extended X-ray absorption fine structure spectra indicate that similar binding mechanisms are present at all pH values and Pb(II) loadings, implying that differences in exchange rates across the pH range examined are not attributable to changes in the coordination environment. The slower exchange at pH 5 may be associated with interparticle and intraparticle diffusion resulting from particle aggregation. These findings demonstrate that the dissolved Pb(II) pool can be rapidly replenished by adsorbed Pb(II) if this pool is drawn down incrementally by biological uptake or a shift in chemical conditions.

Additives, such as ions, small molecules, and macromolecules, have been found to regulate the formation of CaCO 3 and control its morphologies and properties. However, a single additive usually affects dominantly one process in CaCO 3 's formation and is seldom found to significantly affect multiple CaCO 3 formation processes. Here, we used in situ grazing incidence X-ray techniques to observe the heterogeneous formation of CaCO 3 and found that a series of formation processes (i.e., nucleation, growth, and Ostwald ripening) were modulated by sulfate. In the nucleation process, increased interfacial free energy and bulk free energy cooperatively increased the nucleation barrier and decreased nucleation rates. In the growth process, sulfate reduced the electrostatic repulsion between CaCO 3 precursors and nuclei, promoting CaCO 3 growth. This influence on the growth counteracted the inhibition effect in the nucleation process, causing a nearly 100% increase in the volume of heterogeneously formed CaCO 3 . Meanwhile, adsorbed sulfate on CaCO 3 nuclei may poison the surface of smaller CaCO 3 nuclei, inhibiting Ostwald ripening. These revealed sulfate's active roles in controlling CaCO 3 formation advance our understanding of sulfate-incorporated biomineralization and scaling phenomena in natural and engineered aquatic environments.

Lead(IV) oxide (PbO 2 ) is one of the lead corrosion products that forms on the inner surface of lead pipes used for drinking water supply. It can maintain low dissolved Pb(II) concentrations when free chlorine is present. When free chlorine is depleted, PbO 2 and soluble Pb(II) will co-occur in these systems. This study used a stable lead isotope ( 207 Pb) as a tracer to examine the interaction between aqueous Pb(II) and solid PbO 2 at conditions with no net change in dissolved Pb concentration. While the dissolved Pb(II) concentration remained unchanged, significant isotope exchange occurred that indicated that substantial amounts (24.3-35.0% based on the homogeneous recrystallization model) of the Pb atoms in the PbO 2 solids had been exchanged with those in solution over 264 h. Neither α-PbO 2 nor β-PbO 2 displayed a change in mineralogy, particle size, or oxidation state after reaction with aqueous Pb(II). The combined isotope exchange and solid characterization results indicate that redox-driven recrystallization of PbO 2 had occurred. Such redox-driven recrystallization is likely to occur in water that stagnates in lead pipes that contain PbO 2 , and this recrystallization may alter the reactivity of PbO 2 with respect to its stability and susceptibility to reductive dissolution.

Adsorption and subsequent reduction of U(VI) on Fe(II)-bearing clay minerals can control the mobility of uranium in subsurface environments. Clays such as montmorillonite provide substantial amounts of the reactive surface area in many subsurface environments, and montmorillonite-containing materials are used in the storage of spent nuclear fuel. We investigated the extent of reduction of U(VI) by Fe(II)-bearing montmorillonite at different pH values and sodium concentrations using X-ray absorption spectroscopy and chemical extractions. Nearly complete reduction of U(VI) to U(IV) occurred at a low sodium concentration at both pH 3 and 6. At pH 6 and a high sodium concentration, which inhibits U(VI) binding at cation-exchange sites, the extent of U(VI) reduction was only 70%. Surface-bound U(VI) on unreduced montmorillonite was more easily extracted into solution with bicarbonate than surface-bound U(IV) generated by reduction of U(VI) on Fe(II)-bearing montmorillonite. We developed a nonelectrostatic surface complexation model to interpret the equilibrium adsorption of U(IV) on Fe(II)-bearing montmorillonite as a function of pH and sodium concentration. These findings establish the potential importance of structural Fe(II) in low iron content smectites in controlling uranium mobility in subsurface environments.

Efficient conversion of CO-rich gas to methane (CH 4 ) provides an effective energy solution by taking advantage of existing natural gas infrastructures. However, traditional chemical and biological conversions face different challenges. Herein, an innovative biophotoelectrochemistry (BPEC) system using Methanosarcina barkeri -CdS as a biohybrid catalyst was successfully employed for CO methanation. Compared with CO 2 -fed BPEC, BPEC-CO significantly extended the CH 4 producing time by 1.7-fold and exhibited a higher CH 4 yield by 9.5-fold under light irradiation. This superior conversion of CO resulted from the fact that CO could serve as an effective quencher of reactive species along with the photoelectron production. In addition, CO was used as a carbon source either directly or indirectly via the produced CO 2 for M. barkeri . Such a process improved the redox activities of membrane-bound proteins for BPEC methanogenesis. These results were consistent with the transcriptomic analyses, in which the genes for the putative CO oxidation and CO 2 reduction pathways in M. barkeri were highly expressed, while the gene expression for reactive oxygen species detoxification remained relatively stable under light irradiation. This study has provided the first proof-of-concept evidence for sustainable CO methanation under a mild condition in the self-replicating BPEC system.

The stability of RNA in aqueous systems is critical for multiple environmental applications including evaluating the environmental fate of RNA interference pesticides and interpreting viral genetic marker abundance for wastewater-based epidemiology. In addition to biological processes, abiotic reactions may also contribute to RNA loss. In particular, some metals are known to dramatically accelerate rates of RNA hydrolysis under certain conditions (i.e., 37 °C or higher temperatures, 0.15-100 mM metal concentrations). In this study, we investigated the extent to which metals catalyze RNA hydrolysis under environmentally relevant conditions. At ambient temperature, neutral pH, and ∼10 μM metal concentrations, we determined that metals that are stronger Lewis acids (i.e., lead, copper) catalyzed single-stranded (ss)RNA, whereas metals that are weaker Lewis acids (i.e., zinc, nickel) did not. In contrast, double-stranded (ds)RNA resisted hydrolysis by all metals. While lead and copper catalyzed ssRNA hydrolysis at ambient temperature and neutral pH values, other factors such as lowering the solution pH and including inorganic and organic ligands reduced the rates of these reactions. Considering these factors along with sub-micromolar metal concentrations typical of environmental systems, we determined that both ssRNA and dsRNA are unlikely to undergo significant metal-catalyzed hydrolysis in most environmental aqueous systems.

In recent years, off-target herbicide drift has been increasingly reported to lead to damage to nontarget vegetation in the U.S. These reports have coincided with the widespread adoption of genetically modified crops with new herbicide-tolerance traits. Planting crops with these traits may indirectly lead to increased drift both by increasing the use of the corresponding herbicides and by facilitating their use as postemergence herbicides later in the season. While extensive efforts have aimed to reduce herbicide drift, critical uncertainties remain regarding the physiochemical phenomena that drive the entry of herbicides into the atmosphere as well as the atmospheric processes that may influence short- and long-range transport. Resolving these uncertainties will support the development of effective approaches to reduce herbicide drift.

Annual global satellite-based estimates of fine particulate matter (PM 2.5 ) are widely relied upon for air-quality assessment. Here, we develop and apply a methodology for monthly estimates and uncertainties during the period 1998-2019, which combines satellite retrievals of aerosol optical depth, chemical transport modeling, and ground-based measurements to allow for the characterization of seasonal and episodic exposure, as well as aid air-quality management. Many densely populated regions have their highest PM 2.5 concentrations in winter, exceeding summertime concentrations by factors of 1.5-3.0 over Eastern Europe, Western Europe, South Asia, and East Asia. In South Asia, in January, regional population-weighted monthly mean PM 2.5 concentrations exceed 90 μg/m 3 , with local concentrations of approximately 200 μg/m 3 for parts of the Indo-Gangetic Plain. In East Asia, monthly mean PM 2.5 concentrations have decreased over the period 2010-2019 by 1.6-2.6 μg/m 3 /year, with decreases beginning 2-3 years earlier in summer than in winter. We find evidence that global-monitored locations tend to be in cleaner regions than global mean PM 2.5 exposure, with large measurement gaps in the Global South. Uncertainty estimates exhibit regional consistency with observed differences between ground-based and satellite-derived PM 2.5 . The evaluation of uncertainty for agglomerated values indicates that hybrid PM 2.5 estimates provide precise regional-scale representation, with residual uncertainty inversely proportional to the sample size.

Lead oxide (PbO 2 ) has the lowest solubility with free chlorine among Pb corrosion products, but depletion of free chlorine or a switch from free chlorine to monochloramine can cause its reductive dissolution. We previously reported that Cu(II) and Zn(II) inhibited PbO 2 reductive dissolution within 12 h. Here, we expanded on this work by performing longer duration experiments and further exploring the underlying mechanisms. Between 12 and 48 h, Cu(II) and Zn(II) had no discernible effect on PbO 2 reductive dissolution. From 48 to 192 h, Cu(II) and Zn(II) enhanced PbO 2 reductive dissolution. Dissolved oxygen (DO) concentrations followed the same trends as PbO 2 reductive dissolution, indicating that the DO was produced by PbO 2 reductive dissolution. On the basis of extended X-ray absorption fine structure spectra, we hypothesize that the inhibitory effect of Cu(II) and Zn(II) on PbO 2 reductive dissolution (<12 h) is caused by decreasing abundance of protonated sites on the PbO 2 surface. The enhanced dissolution (>48 h) may be caused by competitive adsorption of Cu(II) and Zn(II) with Pb(II), which could limit the adsorption of Pb(II) onto PbO 2 that could otherwise inhibit reductive dissolution. This study indicates that stagnation time plays a vital role in determining cations' effects on the stability of Pb corrosion products.

Unveiling the effects of an environmental abundant anion "sulfate" on the formation of calcium carbonate (CaCO 3 ) is essential to understand the formation mechanisms of biominerals like corals and brachiopod shells, as well as the scale formation in desalination systems. However, it was experimentally challenging to elucidate the sulfate-CaCO 3 interactions at the explicit first step of CaCO 3 formation: nucleation. In addition, there is limited quantitative information on the precise control of nucleation kinetics. Here, heterogeneous CaCO 3 nucleation is monitored in real time as a function of sulfate concentrations (0-10 mM Na 2 SO 4 ) using synchrotron-based grazing incidence X-ray scattering techniques. The results showed that sulfate can be incorporated in the nuclei, resulting in a nearly 90% decrease in the CaCO 3 nucleation rate, causing a 120% increase in the CaCO 3 nucleus size, and inhibiting the vaterite-to-calcite phase transformation. Moreover, this work quantitatively relates sulfate concentrations to the effective interfacial energies of CaCO 3 and finds a non-linear trend, suggesting that CaCO 3 heterogeneous nucleation is more sensitive at a low sulfate concentration. This study can be readily extended to study other additives and obtain quantitative relationships between additive concentrations and CaCO 3 interfacial energies, a key step toward achieving natural and engineered controls on CaCO 3 nucleation.

Detailed offline speciation of gas- and particle-phase organic compounds was conducted using gas/liquid chromatography with traditional and high-resolution mass spectrometers in a hybrid targeted/nontargeted analysis. Observations were focused on an unoccupied home and were compared to two other indoor sites. Observed gas-phase organic compounds span the volatile to semivolatile range, while functionalized organic aerosols extend from intermediate volatility to ultra-low volatility, including a mix of oxygen, nitrogen, and sulfur-containing species. Total gas-phase abundances of hydrocarbon and oxygenated gas-phase complex mixtures were elevated indoors and strongly correlated in the unoccupied home. While gas-phase concentrations of individual compounds generally decreased slightly with greater ventilation, their elevated ratios relative to controlled emissions of tracer species suggest that the dilution of gas-phase concentrations increases off-gassing from surfaces and other indoor reservoirs, with volatility-dependent responses to dynamically changing environmental factors. Indoor-outdoor emissions of gas-phase intermediate-volatility/semivolatile organic hydrocarbons from the unoccupied home averaged 6-11 mg h -1 , doubling with ventilation. While the largest single-compound emissions observed were furfural (61-275 mg h -1 ) and acetic acid, observations spanned a wide range of individual volatile chemical products (e.g., terpenoids, glycol ethers, phthalates, other oxygenates), highlighting the abundance of long-lived reservoirs resulting from prior indoor use or materials, and their gradual transport outdoors.

The hydroxyl radical, • OH, is one of the most reactive free radicals and plays significant roles in the oxidative degradation of organic pollutants and the electron transfer of inorganic ions in natural and engineered environmental processes. To quantitatively determine the contribution of • OH to oxidative reactions, a specific scavenger, such as tert -butyl alcohol (TBA), is usually added to eliminate • OH effects. Although TBA is commonly assumed to transform • OH into oxidatively inert products, this study demonstrates that utilizing TBA as an • OH scavenger generates the secondary peroxyl radical (ROO • ), influencing the oxidation of transition metals, such as Mn. Although ROO • is less reactive than • OH, it has an extended half-life and a longer diffusion distance that enables more redox reactions, such as the oxidation of Mn 2+ (aq) to Mn IV oxide solids. In addition to promoting Mn 2+ (aq) oxidation kinetics, TBA can also affect the crystalline phases, oxidation states, and morphologies of Mn oxide solids. Thus, the oxidative roles of • OH in aqueous redox reactions cannot be examined simply by adding TBA: the effects of secondary ROO • must also be considered. This study urges a closer look at the potential formation of secondary radicals during scavenged oxidative reactions in environmental systems.

Fine particulate air pollution (PM 2.5 ) is a leading contributor to the overall global burden of disease. Traditionally, outdoor PM 2.5 has been characterized using mass concentrations which treat all particles as equally harmful. Oxidative potential (OP) (per μg) and oxidative burden (OB) (per m 3 ) are complementary metrics that estimate the ability of PM 2.5 to cause oxidative stress, which is an important mechanism in air pollution health effects. Here, we provide the first national estimates of spatial variations in multiple measures (glutathione, ascorbate, and dithiothreitol depletion) of annual median outdoor PM 2.5 OB across Canada. To do this, we combined a large database of ground-level OB measurements collected monthly prospectively across Canada for 2 years (2016-2018) with PM 2.5 components estimated using a chemical transport model (GEOS-Chem) and satellite aerosol observations. Our predicted ground-level OB values of all three methods were consistent with ground-level observations (cross-validation R 2 = 0.63-0.74). We found that forested regions and urban areas had the highest OB, predicted primarily by black carbon and organic carbon from wildfires and transportation sources. Importantly, the dominant components associated with OB were different than those contributing to PM 2.5 mass concentrations (secondary inorganic aerosol); thus, OB metrics may better indicate harmful components and sources on health than the bulk PM 2.5 data in future national-level epidemiological studies.2.5 data in future national-level epidemiological studies.

The highly infectious SARS-CoV-2 novel coronavirus has resulted in a global pandemic. More than a hundred million people are already impacted, with infected numbers expected to go up. Coughing, sneezing, and even talking emit respiratory droplets which can carry infectious viruses. It is important to understand how the exhaled particles move through air to an exposed person to better predict the airborne transmission impacts of SARS-CoV-2. There are many studies conducted on the airborne spread of viruses causing diseases such as SARS and measles; however, there are very limited studies that couple the transport characteristics with the aerosol dynamics of the droplets. In this study, a comprehensive model for simultaneous droplet evaporation and transport due to diffusion, convection, and gravitational settling is developed to determine the near spatial and temporal concentration of the viable virus exhaled by the infected individual. The exposure to the viable virus is estimated by calculating the respiratory deposition, and the risk of infection is determined using a dose-response model. The developed model is used to quantify the risk of short-range airborne transmission of SARS-CoV-2 from inhalation of virus-laden droplets when an infected individual is directly in front of the person exposed and the surrounding air is stagnant. The effect of different parameters, such as viral load, infectivity factor, emission sources, physical separation, exposure time, ambient air velocity, dilution, and mask usage, is determined on the risk of exposure.

Adsorption of uranium onto goethite is an important partitioning process that controls uranium mobility in subsurface environments, for which many different surface complexation models (SCMs) have been developed. While individual models can fit the data for which they are parameterized, many perform poorly when compared with experimental data covering a broader range of conditions. There is an imperative need to quantitatively evaluate the variations in the models and to develop a more robust model that can be used with more confidence across the wide range of conditions. We conducted an intercomparison and refinement of the SCMs based on a metadata analysis. By seeking the globally best fit to a composite dataset with wide ranges of pH, solid/sorbate ratios, and carbonate concentrations, we developed a series of models with different levels of complexity following a systematic roadmap. The goethite-uranyl-carbonate ternary surface complexes were required in every model. For the spectroscopically informed models, a triple-plane model was found to provide the best fit, but the performance of the double-layer model with bidentate goethite-uranyl and goethite-uranyl-carbonate complexes was also comparable. Nevertheless, the models that ignore the bidentate feature of uranyl surface complexation consistently performed poorly. The goodness of fitting for the models that ignore adsorption of carbonate and the charge distributions was not significantly compromised compared with that of their counterparts that considered those. This approach of model development for a large and varied dataset improved our understanding of U(VI)-goethite surface reactions and can lead to a path for generating a single set of reactions and equilibrium constants for including U(VI) adsorption onto goethite in reactive transport models.

Phosphodiester bonds in the backbones of double-stranded (ds)RNA and single-stranded (ss)RNA are known to undergo alkaline hydrolysis. Consequently, dsRNA agents used in emerging RNA interference (RNAi) products have been assumed to exhibit low chemical persistence in solutions. However, the impact of the duplex structure of dsRNA on alkaline hydrolysis has not yet been evaluated. In this study, we demonstrated that dsRNA undergoes orders-of-magnitude slower alkaline hydrolysis than ssRNA. Furthermore, we observed that dsRNA remains intact for multiple months at neutral pH, challenging the assumption that dsRNA is chemically unstable. In systems enabling both enzymatic degradation and alkaline hydrolysis of dsRNA, we found that increasing pH effectively attenuated enzymatic degradation without inducing alkaline hydrolysis that was observed for ssRNA. Overall, our findings demonstrated, for the first time, that key degradation pathways of dsRNA significantly differ from those of ssRNA. Consideration of the unique properties of dsRNA will enable greater control of dsRNA stability during the application of emerging RNAi technology and more accurate assessment of its fate in environmental and biological systems, as well as provide insights into broader application areas including dsRNA isolation, detection and inactivation of dsRNA viruses, and prebiotic molecular evolution.

A major challenge in assessing the impact of aerosols on climate change is to understand how human activities change aerosol loading and properties relative to the pristine/preindustrial baseline. Here, we combine chemical transport simulations and field measurements to investigate the effect of anthropogenic pollution from an isolated metropolis on the particle number concentration over the preindustrial-like Amazon rainforest through various new-particle formation (NPF) mechanisms and primary particle emissions. To represent organic-mediated NPF, we employ a state-of-the-art model that systematically simulates the formation chemistry and thermodynamics of extremely low volatility organic compounds, as well as their roles in NPF processes, and further update the model to improve organic NPF simulations under human-influenced conditions. Results show that urban pollution from the metropolis increases the particle number concentration by a factor of 5-25 over the downwind region (within 200 km from the city center) compared to background conditions. Our model indicates that NPF contributes over 70% of the total particle number in the downwind region except immediately adjacent to the sources. Among different NPF mechanisms, the ternary NPF involving organics and sulfuric acid overwhelmingly dominates. The improved understanding of particle formation mechanisms will help better quantify anthropogenic aerosol forcing from preindustrial times to the present day.

Metal components in fine particulate matter (PM 2.5 ) from nontailpipe emissions may play an important role in underlying the adverse respiratory effects of PM 2.5 . We investigated the associations between long-term exposure to iron (Fe) and copper (Cu) in PM 2.5 and their combined impact on reactive oxygen species (ROS) generation in human lungs, and the incidence of asthma, chronic obstructive pulmonary disease (COPD), COPD mortality, pneumonia mortality, and respiratory mortality. We conducted a population-based cohort study of ∼0.8 million adults in Toronto, Canada. Land-use regression models were used to estimate the concentrations of Fe, Cu, and ROS. Outcomes were ascertained using validated health administrative databases. We found positive associations between long-term exposure to Fe, Cu, and ROS and the risks of all five respiratory outcomes. The associations were more robust for COPD, pneumonia mortality, and respiratory mortality than for asthma incidence and COPD mortality. Stronger associations were observed for ROS than for either Fe or Cu. In two-pollutant models, adjustment for nitrogen dioxide somewhat attenuated the associations while adjustment for PM 2.5 had little influence. Long-term exposure to Fe and Cu in PM 2.5 and estimated ROS concentration in lung fluid was associated with increased incidence of respiratory diseases, suggesting the adverse respiratory effects of nontailpipe emissions.

In hydraulic fracturing fluids, the oxidant persulfate is used to generate sulfate radical to break down polymer-based gels. However, sulfate radical may be scavenged by high concentrations of halides in hydraulic fracturing fluids, producing halogen radicals (e.g., Cl • , Cl 2 •- , Br • , Br 2 ). In this study, we investigated how halogen radicals alter the mechanisms and kinetics of the degradation of organic chemicals in hydraulic fracturing fluids. Using a radical scavenger (i.e., isopropanol), we determined that halogenated products of additives such as cinnamaldehyde (i.e., α-chlorocinnamaldehyde and α-bromocinnamaldehyde) and citrate (i.e., trihalomethanes) were generated via a pathway involving halogen radicals. We next investigated the impact of halogen radicals on cinnamaldehyde degradation rates. The conversion of sulfate radicals to halogen radicals may result in selective degradation of organic compounds. Surprisingly, we found that the addition of halides to convert sulfate radicals to halogen radicals did not result in selective degradation of cinnamaldehyde over other compounds (i.e., benzoate and guar), which may challenge the application of radical selectivity experiments to more complex molecules. Overall, we find that halogen radicals, known to react in advanced oxidative treatment and sunlight photochemistry, also contribute to the unintended degradation and halogenation of additives in hydraulic fracturing fluids.•- , and BrCl •- ). In this study, we investigated how halogen radicals alter the mechanisms and kinetics of the degradation of organic chemicals in hydraulic fracturing fluids. Using a radical scavenger (i.e., isopropanol), we determined that halogenated products of additives such as cinnamaldehyde (i.e., α-chlorocinnamaldehyde and α-bromocinnamaldehyde) and citrate (i.e., trihalomethanes) were generated via a pathway involving halogen radicals. We next investigated the impact of halogen radicals on cinnamaldehyde degradation rates. The conversion of sulfate radicals to halogen radicals may result in selective degradation of organic compounds. Surprisingly, we found that the addition of halides to convert sulfate radicals to halogen radicals did not result in selective degradation of cinnamaldehyde over other compounds (i.e., benzoate and guar), which may challenge the application of radical selectivity experiments to more complex molecules. Overall, we find that halogen radicals, known to react in advanced oxidative treatment and sunlight photochemistry, also contribute to the unintended degradation and halogenation of additives in hydraulic fracturing fluids.

We developed Europe-wide models of long-term exposure to eight elements (copper, iron, potassium, nickel, sulfur, silicon, vanadium, and zinc) in particulate matter with diameter <2.5 μm (PM 2.5 ) using standardized measurements for one-year periods between October 2008 and April 2011 in 19 study areas across Europe, with supervised linear regression (SLR) and random forest (RF) algorithms. Potential predictor variables were obtained from satellites, chemical transport models, land-use, traffic, and industrial point source databases to represent different sources. Overall model performance across Europe was moderate to good for all elements with hold-out-validation R -squared ranging from 0.41 to 0.90. RF consistently outperformed SLR. Models explained within-area variation much less than the overall variation, with similar performance for RF and SLR. Maps proved a useful additional model evaluation tool. Models differed substantially between elements regarding major predictor variables, broadly reflecting known sources. Agreement between the two algorithm predictions was generally high at the overall European level and varied substantially at the national level. Applying the two models in epidemiological studies could lead to different associations with health. If both between- and within-area exposure variability are exploited, RF may be preferred. If only within-area variability is used, both methods should be interpreted equally.

Amine-based formulations are widely used to decrease volatilization of carboxylic acid-containing herbicides including dicamba. Despite our reliance on these formulations, the underlying amine properties that determine their ability to control herbicide volatilization are poorly understood. In this study, we measured dicamba volatilization from solid (BAMPA) on glass as with dimethylamine (DMA), diglycolamine (DGA), and N , N -bis(3-aminopropyl)methylamine (BAPMA) as a function of temperature and amine-to-dicamba ratio, as well as in the presence of glyphosate. In all cases, we found that BAPMA had a greater ability to lessen dicamba volatilization than DMA or DGA. Even when only 1 BAPMA molecule was present for every 10 dicamba molecules, dicamba volatilization was still decreased by 70% relative to the free acid case. The particular ability for BAPMA to control dicamba volatilization could be attributed to several molecular features (i.e., molecular weight, type and number of amine functional groups). Using a set including 5 additional amines, we determined that dicamba volatilization is primarily influenced by the number of functional groups in the amine that can participate in hydrogen bonding. From these results, we propose that ability of an amine to form multiple intermolecular interactions (i.e., hydrogen bonds) in the residue may best predict their potential to prevent herbicide volatilization.

China has large anthropogenic chlorine emissions from agricultural fires, residential biofuel, waste incineration, coal combustion, and industrial processes. Here we quantify the effects of chlorine on fine particulate matter (PM 2.5 ) and ozone air quality across China by using the GEOS-Chem chemical transport model with comprehensive anthropogenic emissions and detailed representation of gas-phase and heterogeneous chlorine chemistry. Comparison of the model to observed ClNO 2 , HCl, and particulate Cl - concentrations shows that reactive chlorine in China is mainly anthropogenic, unlike in other continental regions where it is mostly of marine origin. The model is successful in reproducing observed concentrations and their distributions, lending confidence in the anthropogenic chlorine emission estimates and the resulting chemistry. We find that anthropogenic chlorine emissions increase total inorganic PM 2.5 by as much as 3.2 μg m -3 on an annual mean basis through the formation of ammonium chloride, partly compensated by a decrease of nitrate because ClNO 2 formation competes with N 2 O 5 hydrolysis. Annual mean MDA8 surface ozone increases by up to 1.9 ppb, mainly from ClNO 2 chemistry, while reactivities of volatile organic compounds increase (by up to 48% for ethane). We find that a sufficient representation of chlorine chemistry in air quality models can be obtained from consideration of HCl/Cl - thermodynamics and ClNO 2 chemistry, because other more complicated aspects of chlorine chemistry have a relatively minor effect.

Exposure to outdoor fine particulate matter (PM 2.5 ) is a leading risk factor for mortality. We develop global estimates of annual PM 2.5 concentrations and trends for 1998-2018 using advances in satellite observations, chemical transport modeling, and ground-based monitoring. Aerosol optical depths (AODs) from advanced satellite products including finer resolution, increased global coverage, and improved long-term stability are combined and related to surface PM 2.5 concentrations using geophysical relationships between surface PM 2.5 and AOD simulated by the GEOS-Chem chemical transport model with updated algorithms. The resultant annual mean geophysical PM 2.5 estimates are highly consistent with globally distributed ground monitors ( R 2 = 0.81; slope = 0.90). Geographically weighted regression is applied to the geophysical PM 2.5 estimates to predict and account for the residual bias with PM 2.5 monitors, yielding even higher cross validated agreement ( R 2 = 0.90-0.92; slope = 0.90-0.97) with ground monitors and improved agreement compared to all earlier global estimates. The consistent long-term satellite AOD and simulation enable trend assessment over a 21 year period, identifying significant trends for eastern North America (-0.28 ± 0.03 μg/m 3 /yr), Europe (-0.15 ± 0.03 μg/m 3 /yr), India (1.13 ± 0.15 μg/m 3 /yr), and globally (0.04 ± 0.02 μg/m 3 /yr). The positive trend (2.44 ± 0.44 μg/m 3 /yr) for India over 2005-2013 and the negative trend (-3.37 ± 0.38 μg/m 3 /yr) for China over 2011-2018 are remarkable, with implications for the health of billions of people.

The occurrence of aluminum in scales on lead pipes is common. This study aimed to identify factors that influence Al accumulation on oxidized lead surfaces and to determine whether the presence of Al impacts Pb release from corrosion products to water. Al accumulation and Pb release were monitored both with and without the addition of phosphate as a corrosion inhibitor. Pb coupons with corrosion scales were exposed to chlorinated water for up to 198 days to investigate Al accumulation and Pb release. Al accumulation was facilitated by Pb corrosion products, but its accumulation was inhibited by phosphate addition. During the study period, the formation of Al deposits did not affect Pb release when phosphate was absent. In an Al-free system, the addition of 1.0 mg/L phosphate (as P) lowered the dissolved Pb concentration below 1.0 μg/L. In a system containing 200 μg/L Al, the emergence of phosphate's effect on Pb control was delayed, and the dissolved Pb concentration decreased but stabilized at a higher value (10-12 μg/L) than in the Al-free system. Phosphohedyphane (Ca 2 Pb 3 (PO 4 ) 3 Cl) was formed in all phosphate-containing systems, and PbO 2 was formed independent of phosphate addition. The effect of Al on Pb release was probably related to its influence on the composition and morphology of Pb-containing minerals on coupon surfaces. The laboratory study has unavoidable limitations in its ability to simulate all conditions in real lead service lines, but this study still highlights the importance of considering the influence of Al when designing Pb corrosion control strategies.