环境科学与技术最新文献

Chlorofluorocarbons (CFCs) exert a strong greenhouse effect and constitute the largest contributor to ozone depletion. Catalytic removal is considered an effective pathway for eliminating low-concentration CFCs under mild conditions. The key issue is the easy deactivation of the catalysts due to their surface fluorination. We herein report a comparative investigation on catalytic dichlorodifluoromethane (CFC-12) removal in the absence or presence of water over the sulfuric-acid-modified three-dimensionally ordered macroporous vanadia-titania-supported Ru (S-Ru/3DOM VTO) catalysts. The S-Ru/3DOM VTO catalyst exhibited high activity (T_90% = 278 °C at space velocity = 40 000 mL g^-1 h^-1) and good stability within 60 h of on-stream reaction in the presence of 1800 ppm of water due to the improvements in acid site amount and redox ability that promoted the adsorption of CFC-12 and the activation of C-F bonds. Compared with the case under dry conditions, catalytic performance for CFC-12 removal was better over the S-Ru/3DOM VTO catalyst in the presence of water. Water introduction mitigated surface fluorination by the replenishment of hydroxyl groups, inhibited the formation of halogenated byproducts via the surface fluorine species cleaning effect, and promoted the reaction pathway of COX₂ (X = Cl/F) → carboxylic acid → CO₂.

Dissecting the photochemical reactivity of metal ions is a significant contribution to understanding secondary pollutant formation, as they have a role to be reckoned with atmospheric chemistry. However, their photochemical reactivity has received limited attention within the active nitrogen cycle, particularly at the gas-solid interface. In this study, we delve into the contribution of magnesium ion (Mg²⁺) and ferric ion (Fe³⁺) to nitrate decomposition on the surface of photoactive mineral dust. Under simulated sunlight irradiation, the observed NO_X production rate differs by an order of magnitude in the presence of Mg²⁺ (6.02 × 10^-10 mol s^-1) and Fe³⁺ (2.07 × 10^-11 mol s^-1). The markedly decreased fluorescence lifetime induced by Mg²⁺ and the change in the valence of Fe³⁺ revealed that Mg²⁺ and Fe³⁺ significantly affect the concentration of nitrate decomposition products by distinct photochemical reactivity with photogenerated electrons. Mg²⁺ promotes NO_X production by accelerating charge transfer, while Fe³⁺ hinders nitrate decomposition by engaging in a redox cyclic reaction with Fe²⁺ to consume photogenerated carriers continuously. Furthermore, when Fe³⁺ coexists with other metal ions (e.g., Mg²⁺, Ca²⁺, Na⁺, and K⁺) and surpasses a proportion of approximately 12%, the photochemical reactivity of Fe³⁺ tends to be dominant in depleting photogenerated electrons and suppressing nitrate decomposition. Conversely, below this threshold, the released NO_X concentration increases sharply as the proportion of Fe³⁺ decreases. This research offers valuable insights into the role of metal ions in nitrate transformation and the generation of reactive nitrogen species, contributing to a deep understanding of atmospheric photochemical reactions.

Elevated levels of atmospheric molecular chlorine (Cl₂) have been observed during the daytime in recent field studies in China but could not be explained by the current chlorine chemistry mechanisms in models. Here, we propose a Cl₂ formation mechanism initiated by aerosol iron photochemistry to explain daytime Cl₂ formation. We implement this mechanism into the GEOS-Chem chemical transport model and investigate its impacts on the atmospheric composition in wintertime North China where high levels of Cl₂ as well as aerosol chloride and iron were observed. The new mechanism accounts for more than 90% of surface air Cl₂ production in North China and consequently increases the surface air Cl₂ abundances by an order of magnitude, improving the model's agreement with observed Cl₂. The presence of high Cl₂ significantly alters the oxidative capacity of the atmosphere, with a factor of 20-40 increase in the chlorine radical concentration and a 20-40% increase in the hydroxyl radical concentration in regions with high aerosol chloride and iron loadings. This results in an increase in surface air ozone by about 10%. This new Cl₂ formation mechanism will improve the model simulation capability for reactive chlorine abundances in the regions with high emissions of chlorine and iron.

There is a notable lack of continuous monitoring of air pollutants in the Global South, especially for measuring chemical composition, due to the high cost of regulatory monitors. Using our previously developed low-cost method to quantify black carbon (BC) in fine particulate matter (PM_2.5) by analyzing reflected red light from ambient particle deposits on glass fiber filters, we estimated hourly ambient BC concentrations with filter tapes from beta attenuation monitors (BAMs). BC measurements obtained through this method were validated against a reference aethalometer between August 2 and 23, 2023 in Addis Ababa, Ethiopia, demonstrating a very strong agreement (R² = 0.95 and slope = 0.97). We present hourly BC for three cities in sub-Saharan Africa (SSA) and one in North America: Abidjan (Côte d'Ivoire), Accra (Ghana), Addis Ababa (Ethiopia), and Pittsburgh (USA). The average BC concentrations for the measurement period at the Abidjan, Accra, Addis Ababa Central summer, Addis Ababa Central winter, Addis Ababa Jacros winter, and Pittsburgh sites were 3.85 μg/m³, 5.33 μg/m³, 5.63 μg/m³, 3.89 μg/m³, 9.14 μg/m³, and 0.52 μg/m³, respectively. BC made up 14-20% of PM_2.5 mass in the SSA cities compared to only 5.6% in Pittsburgh. The hourly BC data at all sites (SSA and North America) show a pronounced diurnal pattern with prominent peaks during the morning and evening rush hours on workdays. A comparison between our measurements and the Goddard Earth Observing System Composition Forecast (GEOS-CF) estimates shows that the model performs well in predicting PM_2.5 for most sites but struggles to predict BC at an hourly resolution. Adding more ground measurements could help evaluate and improve the performance of chemical transport models. Our method can potentially use existing BAM networks, such as BAMs at U.S. Embassies around the globe, to measure hourly BC concentrations. The PM_2.5 composition data, thus acquired, can be crucial in identifying emission sources and help in effective policymaking in SSA.

The majority of microplastics (MPs) found in the environment originate from plastic fragmentation occurring in the environment and are influenced by environmental factors such as UV irradiation and biotic interactions. However, the effects of river drying on plastic fragmentation remain unknown, despite the global prevalence of watercourses experiencing flow intermittence. This study investigates, through laboratory experiments, the coupled effects of drying duration and UV irradiation on PVC film fragmentation induced by artificial mechanical abrasion. This study shows that PVC film fragmentation increases with drying duration through an increase in the abundance and size of formed MPs as well as mass loss from the initial plastic item, with significant differences for drying durations >50% of the experiment duration. The average abundance of formed MPs in treatments exposed to severe drying duration was almost two times higher than in treatments nonexposed to drying. Based on these results, we developed as a proof of concept an Intermittence-Based Plastic Fragmentation Index that may provide insights into plastic fragmentation occurring in river catchments experiencing large hydrological variability. The present study suggests that flow intermittence occurring in rivers and streams can lead to increasing plastic fragmentation, unraveling new insights into plastic pollution in freshwater systems.

Sewage sludge, as a carbon-rich byproduct of wastewater treatment, holds significant untapped potential as a renewable resource. Upcycling this troublesome waste stream represents great promise in addressing global escalating energy demands through its wide practice of biochemical recovery concurrently. Here, we propose a biotechnological concept to gain value-added liquid bioproducts from sewage sludge in a self-sufficient manner by directly transforming sludge into medium-chain fatty acids (MCFAs). Our findings suggest that yeast, a cheap and readily available commercial powder, would involve ethanol-type fermentation in chain elongation to achieve abundant MCFA production from sewage sludge using electron donors (i.e., ethanol) and acceptors (i.e., short-chain fatty acids) produced in situ. The enhanced abundance and transcriptional activity of genes related to key enzymes, such as butyryl-CoA dehydrogenase and alcohol dehydrogenase, affirm the robust capacity for the self-sustained production of MCFAs. This is indicative of an effective metabolic network established between yeast and anaerobic microorganisms within this innovative sludge fermentation framework. Furthermore, life cycle assessment and techno-economic analysis evidence the sustainability and economic competitiveness of this biotechnological strategy. Overall, this work provides insights into sewage sludge upgrading independent of additional carbon input, which can be applied in existing anaerobic sludge fermentation infrastructure as well as to develop new applications in a diverse range of industries.