Environmental Science & Technology Letters Environ.最新文献

Organic alkoxy (RO) and peroxy (RO₂) radicals are key intermediates in multiphase atmospheric oxidation chemistry, though most of the study of their chemistry has focused on the gas phase. To better understand how radical chemistry may vary across different phases, we examine the chemistry of a model system, the 1-pentoxy radical, in three phases: the aqueous phase, the condensed organic phase, and the gas phase. In each phase, we generate the 1-pentoxy radical from the photolysis of n-pentyl nitrite, run the chemistry under conditions in which RO₂ radicals react with NO, and detect the products in real time using an ammonium chemical ionization mass spectrometer (NH₄⁺ CIMS). The condensed-phase chemistry shows an increase in formation of organic nitrate (RONO₂) from the downstream RO₂+NO reaction, which is attributed to potential collisional and solvent-cage stabilization of the RO₂–NO complex. We further observe an enhancement in the yield of carbonyl relative to hydroxy carbonyl products in the condensed phase, indicating changes to RO radical kinetics. The different branching ratios in the condensed phase impact the product volatility distribution as well as HO_x-NO_x chemistry, and may have implications for nitrate formation, aqueous aerosol formation, and radical cycling within atmospheric particles and droplets.

Successful reduction of oil and gas sector methane emissions to meet near-zero intensity targets requires the identification and mitigation of all possible sources. One potentially important source is catalytic heaters, which have largely escaped attention in regulatory and mitigation efforts despite being ubiquitous at upstream production sites in cold climate regions. This study reports direct in situ measurements of the exhaust streams of 38 natural gas-fired catalytic heaters at upstream production sites in British Columbia, Canada. All heaters in the sample showed consistently poor methane conversion with mean destruction efficiencies of 61 ± 5% while releasing 235 [+31/–28] g of methane per cubic meter of fuel. Although individual units are generally small methane sources (mean of 0.28 ± 0.04 kg/h), their prevalence means they could represent 6% of the total provincial upstream methane inventory and as an aggregate methane source could be 5× more significant than abandoned wells. Notably, these heaters are seasonal sources whose emissions would be missed in measurement campaigns occurring solely in summer months. However, additional measurements from a small number of heat medium burners demonstrate that, where feasible, methane emissions can be reduced by approximately 425× by replacing catalytic heaters with centralized heat systems.

Phosphogypsum (PG) wastes, including solid-state PG and liquid-state PG leachate, are industrial byproducts generated during the production of phosphoric acid. It is of great concern due to the large-scale product accumulation and environmental and geological hazards. Harmless treatment and green chemical resource utilization techniques emerge to be the critical solutions for solving the PG waste problem. This review aims to comprehensively summarize the recent advances in harmless treatment, resource recovery, and valorization of PG wastes. The technique advancements regarding the harmless treatment, decontamination, and valorization of solid-state PG waste with different physical, chemical, thermal, and biological approaches are summarized. Additionally, the comprehensive physical chemistry mechanisms underneath the treatment and valorization strategies for PG leachate have also been discussed. For future work, the challenges and perspectives for resource utilization of solid-state PG and leachate are highlighted. With the systematic information on these aspects, we expect this review will serve as a guideline for the young generations working on PG waste treatment and resource recovery.

Advancements within fecal source tracking (FST) studies are complicated by a lack of knowledge regarding the genetic content and distribution of fecally shed microbial populations. To address this gap, we performed a systematic literature review and curated a large collection of genomes (n = 26,018) representing fecally shed prokaryotic species across broad and narrow source categories commonly implicated in FST studies of recreational waters (i.e., cats, dogs, cows, seagulls, chickens, pigs, birds, ruminants, human feces, and wastewater). We find that across these sources the total number of prokaryotic genomes recovered from materials meeting our initial inclusion criteria varied substantially across fecal sources: from none in seagulls to 9,085 in pigs. We examined genome sequences recovered from these metagenomic and isolation-based studies extensively via comparative genomic approaches to characterize trends across source categories and produce a finalized genome database for each source category which is available online (n = 12,730). On average, 81% of the genomes representing species-level populations occur only within a single source. Using fecal slurries to test the performance of each source database, we report read capture rates that vary with fecal source alpha diversity and database size. We expect this resource to be useful to FST-related objectives, One Health research, and sanitation efforts globally.

Chemical transformation of 2-methyltetrol sulfates (2-MTS), key isoprene-derived secondary organic aerosol (SOA) constituents, through heterogeneous hydroxyl radical (^•OH) oxidation can result in the formation of previously unidentified atmospheric organosulfates (OSs). However, detected OSs cannot fully account for the sulfur content released from reacted 2-MTS, indicating the existence of sulfur in forms other than OSs such as inorganic sulfates. This work investigated the formation of inorganic sulfates through heterogeneous ^•OH oxidation of 2-MTS aerosols. Remarkably, high yields of inorganic sulfates, defined as the moles of inorganic sulfates produced per mole of reacted 2-MTS, were observed in the range from 0.48 ± 0.07 to 0.68 ± 0.07. These could be explained by the production of sulfate (SO₄^•–) and sulfite (SO₃^•–) radicals through the cleavage of C–O(S) and (C)O–S bonds, followed by aerosol-phase reactions. Additionally, nonsulfated products resulting from bond cleavage were likely volatile and evaporated into the gas phase, as evidenced by the observed aerosol mass loss (≤25%) and concurrent size reduction upon oxidation. This investigation highlights the significant transformation of sulfur from its organic to inorganic forms during the heterogeneous oxidation of 2-MTS aerosols, potentially influencing the physicochemical properties and environmental impacts of isoprene-derived SOAs.

China is suffering from frequent PM_2.5 episodes in the winter characterized by rapid particle growth. Organic aerosol (OA) is often the bottleneck of further reducing PM pollution. To devise effective control measures, the sources of OA must be identified and quantified first. This study expanded the capability of cutting-edge iodide-based chemical ionization mass spectrometry in a source apportionment study by measuring a variety of oxygenated organic molecules (OOMs). A workflow was developed to find suitable tracers from these OOMs. The source apportionment research of OAs was advanced by incorporating these OOM tracers with traditional nonpolar/polar organic tracers. The OOMs-incorporated positive matrix factorization (PMF) was applied to two unique groups of aerosol samples collected in an inland megacity and an ocean expedition. PMF without OOM tracers overestimated the OA contribution from fossil fuel combustion, plastic burning, and monoterpene SOA. On average, PMF with OOM tracers assigned 28.8% and 44.1% of OA in inland megacity and marine samples, respectively, to 4 new factors: aliphatic SOA, highly oxidized aromatic SOA, sulfur-containing SOA, and nitrogen-containing SOA. A one-hour resolution measurement found nitrogen-containing SOA and sulfur-containing SOA were significantly enhanced in particles during nighttime and daytime particle growth events, respectively.

In environmental chemistry research, stock solutions of organic compounds are commonly prepared in alcohols (e.g., methanol), including during experiments to quantify oxidation kinetics and disinfection byproduct formation. Lacking an obviously oxidizable functional group, alcohols are tacitly assumed to be inert with respect to common water treatment oxidants and favored for their low cost, low toxicity, and miscibility with water. While attempting to duplicate a previous result reporting formaldehyde as a product of dimethylamine chlorination, we found that a substantial amount of formaldehyde was generated when the dimethylamine dosing solution was prepared in methanol but not when it was prepared in water. We further found that under conditions typical of chlorination kinetics experiments, aqueous methanol concentrations as low as 0.4% (v/v) could significantly deplete chlorine compared to methanol-free controls. In the presence of increasing methanol concentrations, chlorine depletion half-lives decreased to ∼4 h at 2% methanol. Finally, we examined the chlorination of five primary alcohols and one secondary alcohol, which all formed the corresponding carbonyls at comparable rates. These findings raise doubts about the routine use of alcohols as carrier solvents for the preparation of stock solutions in research on aqueous chlorination reactions and highlight alcohols as a potential source of aldehyde formation during chlorination.

Hydrochar, a biochar variant produced through hydrothermal carbonization (HTC), is increasingly reported to exhibit superior performance in mitigating soil nitrous oxide (N₂O) emissions, relative to traditional biochar produced through high-temperature pyrolysis (pyrochar). However, the underlying mechanisms for this are still unclear. In this study, we conducted a comprehensive comparative analysis of hydrochar and pyrochar, examining the soil N₂O mitigation potential from denitrification, electron shuttle functionality, soil microbial composition, and denitrification genes dynamics. Our results conclusively establish that hydrochar outperforms pyrochar due to its exceptional electron transfer capacity, characterized by higher electron exchange capacity (EEC), abundance of electron-donating moieties and more prevalent electron transfer components. Notably, the lower concentration of persistent free radicals (PFRs) in hydrochar results in unimpeded expression of the nosZ gene, promoting complete denitrification and resulting in reduced N₂O emissions. These findings highlight hydrochar’s potential as an electron shuttle and underscore its promise as a superior soil amendment for mitigating N₂O emissions compared to pyrochar.

A global perspective on the abundance and formation of organosulfates (OSs) during field studies (relative humidity of 53% to 77%) suggested that the investigated particles are generally nondry and acidic (pH < 6). However, the key factors affecting OS formation in nearly dry and weakly acidic aerosol conditions remain elusive. This topic was resolved by examining the composition and formation of OSs in PM_2.5 collected in Urumqi (dry and dusty) over a one-year period. Anthropogenic OSs accounted for 49 ± 8% of the total OSs, indicating a large anthropogenic contribution to OS formation in Urumqi (particularly in winter). The low aerosol liquid water (ALW) concentration (2 ± 2 μg m^–3) and weak particle acidity (pH = 7 ± 2) during the summer were important factors limiting anthropogenic OS formation. However, increased ALW (100 ± 70 μg m^–3) and particle acidity (pH = 5 ± 1) during the winter significantly promoted anthropogenic OS production. The formation of most of isoprene- and monoterpene-derived OSs during summer was also constrained by unfavorable ALW concentration and particle acidity, resulting in biogenic OS levels being lower in summer than in winter. This study provides observational evidence on OS formation constraints by dry and dusty atmospheric conditions.

This study developed a novel molecularly imprinted polymer (MIP) that is both conductive and redox-active for directly quantifying perfluorooctanoic acid (PFOA) electrochemically. We synthesized the monomer 3,4-ethylenedioxythiophene-2,2,6,6-tetramethylpiperidinyloxy (EDOT-TEMPO) for electropolymerization on a glassy carbon electrode using PFOA as a template, which was abbreviated as PEDOT-TEMPO-MIP. The redox-active MIP eliminated the need for external redox probes. When exposed to PFOA, both anodic and cathodic peaks of MIP showed a decreased current density. This observation can be explained by the formation of a charge-assisted hydrogen bond between the anionic PFOA and MIP’s redox-active moieties (TEMPO) that hinder the conversion between the oxidized and reduced forms of TEMPO. The extent of the current density decrease showed excellent linearity with PFOA concentrations, with a method detection limit of 0.28 ng·L^–1. PEDOT-TEMPO-MIP also exhibited high selectivity toward PFOA against other per- and polyfluoroalkyl substances (PFAS) at environmentally relevant concentrations. Our results suggest electropolymerization of MIPs was highly reproducible, with a relative standard deviation of 5.1% among three separate MIP electrodes. PEDOT-TEMPO-MIP can also be repeatedly used with good stability and reproducibility for PFOA detection. This study provides an innovative platform for rapid PFAS quantification using redox-active MIPs, laying the groundwork for developing compact PFAS sensors.