Environmental Science & Technology Letters Environ.最新文献

Determining the pH of hypersaline wastewater is essential for regulatory compliance and the feasibility of geochemical and treatment processes. Hypersaline solutions have high ionic strength, which introduces deviations among measured proton activity, its concentration, and potential acidity. Here, we evaluate these deviations with theoretical simulations and by modeling hypersaline lithium brines from South America and produced waters from U.S. oil and gas operations (n > 60 000). We show that when the ionic strength increases above 2 m, proton activity coefficients steadily increase above unity. This causes the pH value to overestimate proton concentration. As this discrepancy increases, the pH alone cannot be used to accurately evaluate the solution’s corrosivity by features such as the saturation index (SI) or calcium carbonate precipitation potential (CCPP). Our analysis reveals that 5% of the investigated produced waters showed pH values of <6 but positive CCPP or SI values, undermining pH as a single regulatory indicator of corrosivity. Accurate evaluation of hypersaline effluent corrosivity requires the utilization of advanced tools such as the PHREEQC software with the Pitzer model. This approach ensures a more reliable characterization of the potential hypersaline effluent corrosivity and thus more efficient management and policy.

The January 2025 Los Angeles wildfires released large amounts of air pollutants and exposed millions of residents to smoke containing hazardous volatile organic compounds (VOCs). To assess exposure risks, we conducted indoor and outdoor VOCs sampling at 22 households near the Palisades and Eaton Fires across three phases: active burning with less than 50% containment (January 8–15), active burning period with more than 50% containment (January 24–31), and postfire (February 11–18). Outdoor benzene concentrations peaked during Phase 1, with a median (interquartile range) of 0.38 (0.27) ppb, decreased over time, and remained below the California Office of Environmental Health Hazard Assessment health benchmarks. Compared with the active burning period, indoor-to-outdoor ratios of m,p-xylene (p = 0.004), carbon tetrachloride (p = 0.002), and heptane (p = 0.02) were significantly higher in the postfire period. Elevated VOC levels were particularly evident in uninhabited homes within burn zones, suggesting ongoing indoor emissions from smoke-impacted materials. These findings raise concerns about indoor air quality postwildfire and the potential for prolonged exposure, underscoring the need for targeted mitigation and ongoing monitoring to protect public health during recovery.

Atmospheric nitrophenols (NPs) undergo visible-light-driven photolysis that significantly impacts reactive nitrogen cycling, yet their structural complexity hinders accurate impact assessment. Here, we reveal a structure-dependent photolysis mechanism of NPs adsorbed on photoactive particulate matter. The visible photolysis rates of representative NPs, such as J_{4-nitroguaiacol} > J_{4-nitrocatechol} > J_{5-nitrosalicylic acid}, span 3 orders of magnitude, closely linked to the chemical reactivity of the nitro group (−NO₂) site in NPs. The interfacial photochemistry process shows differential depletion of the −NO₂ groups, consistent with their relative reactivities. Calculated average local ionization energy (ALIE) values serve as a predictive descriptor of visible photolysis potential, with lower ALIE correlating with faster photolysis. Validation across 10 atmospheric NPs supports the universal correlation between the visible photolysis rate and ALIE value, enabling prioritization of high-risk species and offering molecular-level insight into the photochemical transformation of complex organic pollutants.

Plasma-assisted nitrogen fixation offers a promising pathway for sustainable ammonia and nitrate synthesis under ambient conditions, yet its energy efficiency remains a major bottleneck. This study presents an interpretable machine learning framework that integrates ensemble learning and SHAP-based analysis to accurately predict and optimize the energy consumption of plasma–water-based nitrogen fixation (PWNF) systems. A total of 224 experimental observations from 21 discharge configurations were used to train and evaluate eight regression algorithms, including XGBoost, CatBoost, and SVR. The best-performing stacking ensemble, led by XGBoost as a meta-learner, achieved a test set R² of 0.966 and a RMSE of 10.17 MJ/mol, demonstrating excellent accuracy and generalization. SHAP and partial dependence plot analyses identified key variables─such as power, nitrogen percentage, discharge frequency, and water vapor content─and revealed their nonlinear contributions to energy efficiency. Furthermore, bivariate PDPs uncovered synergistic interactions (e.g., between power and gas composition) that guide multiparameter optimization strategies. Experimental validation confirmed the model’s robustness, with prediction errors of less than 7% for boundary cases. This framework not only advances predictive modeling in plasma engineering but also provides actionable insights into the parametric tuning of nitrogen fixation systems. The approach can be scaled to other plasma-assisted or hybrid electrochemical nitrogen conversion routes.

Additive electronic air cleaners like ionizers, photocatalytic oxidizers, and plasma devices intentionally release reactive species into indoor air so that they may inactivate infectious airborne pathogens. Third-party commercial testing and peer-reviewed studies alike typically report inactivation metrics in terms of percent- or log-reductions observed from chamber experiments that imply a nearly complete elimination of infection risks. However, these metrics are highly dependent upon the experimental volume and duration, so they do not directly translate to actual effectiveness indoors. We reviewed 45 experiments across 14 published studies and converted reported reduction metrics into equivalent clean airflow rates (ECA). Different studies yielded distinct ECA distributions, suggesting that differences in experimental procedures, device specifications, or environmental conditions may be more important ECA determinants than the target pathogen or the underlying device technology. Study-averaged ECAs spanned between 1.4 and 134 m³/h, with the median study having an average ECA = 31 m³/h. Even small off-the-shelf HEPA-filter air cleaners typically provide ECAs that exceed the best-performing additive devices analyzed herein. Their low efficacy relative to alternatives, environmental factors that can affect performance, and chemical byproduct concerns are discussed in the context of test standard development and system selection.

Peroxyacetyl nitrate (PAN) is an important tracer of photochemistry formed through the oxidation of nonmethane volatile organic compounds (NMVOCs) in the presence of nitrogen oxides (NO_x ≡ NO + NO₂). We use CrIS satellite observations and GEOS-Chem simulations to identify a persistent hotspot of free tropospheric PAN over the Sichuan Basin (SCB) in China during winter. The basin topography promotes the initial vertical lifting, while the subsequent temperature inversion layer in the free troposphere (FT) traps the lifted NO_x and NMVOCs, thereby facilitating PAN formation. Budget analysis for a 3-D box representing the SCB FT (825–215 hPa) shows that photochemical production accounts for 73% of PAN formation, while vertical transport from below contributes 27%. Dominant photochemical PAN formation stems from stagnant air masses enabling sufficient oxidation of precursors and low winter temperatures prolonging PAN lifetime. Horizontal transport dominates PAN removal (50%), suggesting the SCB as a winter source of PAN and NO_x to downwind regions. This study highlights that meteorology and terrain drive severe winter PAN pollution in the SCB.

Perfluoroalkyl acids (PFAAs), particularly perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS), can be emitted into the atmosphere via sea spray aerosols (SSA), contributing to long-range airborne transport of pollutants. However, the role of sea surface temperature (SST) in modulating this emission remains unclear. This study systematically investigates the impact of SST on PFAAs enrichment in SSA using laboratory experiments and global emission modeling. Results show that higher SST can significantly promote the enrichment of PFAAs in SSA (particularly in submicrometer SSA), due to increased bubble collision efficiency and surface-active behavior of PFAAs. The enrichment factors (EFs) at 25 °C were 1–2 orders of magnitude higher than those at 4 °C, with a stronger SST dependence for longer-chain PFAAs. When considering SST effects, the estimated global emission fluxes of PFOA and PFOS are approximately 3.1 and 2.7 times the previously calculated values, respectively. These findings highlight SST as a critical regulator of PFAAs sea–air transfer, emphasizing the need to integrate temperature-dependent enrichment mechanisms into global models for accurate assessment of atmospheric PFAAs transport and environmental impact.

Colloidal activated carbon (CAC) is a promising material for in situ remediation of groundwater impacted by per- and polyfluoroalkyl substances (PFAS). However, long-term aging of CAC in the subsurface can trigger particle mobilization, threatening barrier integrity and increasing the risk of CAC-facilitated PFAS transport. Here, we systematically investigate how aging processes influence CAC mobilization from saturated porous media. CAC was subjected to physical, chemical (H₂O₂, Fenton, acid), and biological aging to mimic wet–dry cycling, oxidation, and biotic transformations relevant to soil–groundwater systems. Physicochemical characterization (surface charge and particle size) showed that most aging treatments increased CAC’s negative surface charge and structural fragility. These changes were accompanied by enhanced CAC mobilization in column experiments under stepwise salinity reduction (100 → 10 → 0.1 mM). In contrast, the slightly suppressed mobilization of Fenton-aged CAC suggests that dissolved Fe²⁺ interacts with CAC by neutralizing surface charge and forming iron oxide precipitates, decreasing electrostatic repulsion. Extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) simulations captured how aging-induced changes in surface charge and particle size modify the mobilization energy barrier. These results reveal the critical role of aging in controlling CAC retention in in situ barriers and highlight the utility of interfacial interaction modeling for elucidating colloid mobilization mechanisms.

Hydrophobic organic compounds (HOCs) such as naphthalene are persistent environmental contaminants whose mobility and bioavailability challenge conventional remediation. Sorptive amendments such as biochar can reduce HOC mobility but may introduce pollutants and lose sorption capacity over time. In this work, we investigated whether the bacterium Bacillus subtilis, biochar, and mixtures of bacteria and biochar could seal pores and impede naphthalene diffusion. We employed two experimental approaches: (i) centrifugation-compacted layers over solid naphthalene (simulating source-zone conditions) and (ii) bioreactors with 3 and 12 μm membranes representing distal transport. B. subtilis exhibited a higher sorption affinity than biochar alone (Freundlich capacity or log K_F of 4.33 vs 3.47) and reduced naphthalene mobilization 3-fold, releasing only 2% of the applied mass. The mixture of biochar and bacteria achieved the greatest reductions in naphthalene flux (70% and 50% for 3 and 12 μm membranes, respectively), with effective diffusivities 2 orders of magnitude lower than molecular diffusion through water. Electron microscopy confirmed pore occlusion by bacterial extracellular polymeric substances and biochar aggregation. These findings demonstrate microbial pore sealing as a promising strategy to limit HOC diffusion in porous media, with potential applications for source-zone and plume containment.

The hygroscopic phase transition (HPT) latent heat of black carbon (BC) particles can affect the atmospheric energy budget. However, the source-dependent characteristics and underlying mechanisms remain poorly understood. Herein, three representative BCs (Corn Cob BC, Camphor Wood BC, and Coal BC) were systematically analyzed to quantify HPT latent heat and reveal component-specific contributions. By combining component-resolved analysis with differential scanning calorimetry, it was found that Coal BC exhibited the highest HPT latent heat at 97% RH (ΔH = 93.77 J g^–1), which was approximately 253 times higher than that at 11% RH (ΔH = 0.37 J g^–1). This was primarily driven by its inorganic component, including the water-extractable fraction (WEBC) and water-extractable minerals (WEM). The corresponding spectral shifts of WEBC (85–100 cm^–1 blueshift) and WEM (100–105 cm^–1 redshift) in O–H stretching bands under 97% RH indicate strong hydrogen-bonding and solvent effects. These inorganic-rich fractions, although accounting for only 10.1–18.0 wt % in Coal BC, controlled water uptake and latent-heat release, highlighting their pivotal role in BC’s nonlinear thermodynamic behavior. This is the first study to quantitatively resolve BC’s HPT latent heat and attribute it to specific components, providing thermodynamic insights for improving the parametrization of BC radiative effects in atmospheric models.