OH Production Research Articles

Efficient hydroxyl radical production and sulfanilamide degradation during oxygenation of microbially reduced metal–organic frameworks

Incubation of iron-reducing bacteria with Fe(III) could generate •OH to decompose organic pollutants under redox fluctuation conditions. However, the Fe(III)/Fe(II) transformation efficiency and therefore yields of •OH production in systems using Fe(III)-bearing minerals as respiration substrate of bacteria is unsatisfying. Here, we showed that different iron- and iron-copper-based metal–organic frameworks (Fe-MOFs and FeCu-MOFs) can mediate electron transfer from Shewanella oneidensis MR-1 to O2 through their Fe(III)/Fe(II) cycling during anoxic–oxic transition, resulting in generation of reactive oxygen species including •O2–, H2O2 and •OH. While 3 g/L of MIL-101(Fe) demonstrated faster Fe(III)/Fe(II) cycling, better yields of •OH production (69.0 μmol/mmol Fe(II) oxidation) and sulfanilamide removal (81.5 % in 24 h) than iron-bearing minerals and the rest two Fe-MOFs (MIL-53(Fe) and MIL-88B(Fe)), Fe0.75Cu0.25-B surpassed the performance of MIL-101(Fe) and other FeCu-MOFs with different Fe/Cu ratios, which might be attributed to its larger surface area, higher amounts of associated Fe(II), and synergistic effects between Fe and Cu species. Moreover, both MIL-101(Fe) and Fe0.75Cu0.25-B maintained structure stability and persistent catalytic activity during four continuous redox cycles in 48 h, the •OH production and sulfanilamide degradation of which exceeded those of one-time operation in the same duration. This study revealed the efficacy of combining bacteria and MOFs for •OH production, and provided promising alternatives for oxidative degradation of contaminants.

Induction of Extracellular Hydroxyl Radicals Production in the White-Rot Fungus Pleurotus eryngii for Dyes Degradation: An Advanced Bio-oxidation Process.

Among pollution remediation technologies, advanced oxidation processes (AOPs) are genuinely efficient since they are based on the production of strong, non-selective oxidants, mainly hydroxyl radicals (·OH), by a set of physicochemical methods. The biological counterparts of AOPs, which may be referred to as advanced bio-oxidation processes (ABOPs), have begun to be investigated since the mechanisms of induction of ·OH production in fungi are known. To contribute to the development of ABOPs, advanced oxidation of a wide number of dyes by the white-rot fungus Pleurotus eryngii, via a quinone redox cycling (QRC) process based on Fenton's reagent formation, has been described for the first time. The fungus was incubated with 2,6-dimethoxy-1,4-benzoquinone (DBQ) and Fe3+-oxalate, with and without Mn2+, leading to different ·OH production rates, around twice higher with Mn2+. Thanks to this process, the degradative capacity of the fungus increased, not only oxidising dyes it was not otherwise able to, but also increasing the decolorization rate of 20 dyes by more than 7 times in Mn2+ incubations. In terms of process efficacy, it is noteworthy that with Mn2+ the degradation of the dyes reached values of 90-100% in 2-4 h, which are like those described in some AOPs based on the Fenton reaction.

Redox‐Active Ferrocene Quencher‐Based Supramolecular Nanomedicine for NIR‐II Fluorescence‐Monitored Chemodynamic Therapy

AbstractReal‐time monitoring of hydroxyl radical (⋅OH) generation is crucial for both the efficacy and safety of chemodynamic therapy (CDT). Although ⋅OH probe‐integrated CDT agents can track ⋅OH production by themselves, they often require complicated synthetic procedures and suffer from self‐consumption of ⋅OH. Here, we report the facile fabrication of a self‐monitored chemodynamic agent (denoted as Fc‐CD‐AuNCs) by incorporating ferrocene (Fc) into β‐cyclodextrin (CD)‐functionalized gold nanoclusters (AuNCs) via host–guest molecular recognition. The water‐soluble CD served not only as a capping agent to protect AuNCs but also as a macrocyclic host to encapsulate and solubilize hydrophobic Fc guest with high Fenton reactivity for in vivo CDT applications. Importantly, the encapsulated Fc inside CD possessed strong electron‐donating ability to effectively quench the second near‐infrared (NIR‐II) fluorescence of AuNCs through photoinduced electron transfer. After internalization of Fc‐CD‐AuNCs by cancer cells, Fenton reaction between redox‐active Fc quencher and endogenous hydrogen peroxide (H2O2) caused Fc oxidation and subsequent NIR‐II fluorescence recovery, which was accompanied by the formation of cytotoxic ⋅OH and therefore allowed Fc‐CD‐AuNCs to in situ self‐report ⋅OH generation without undesired ⋅OH consumption. Such a NIR‐II fluorescence‐monitored CDT enabled the use of renal‐clearable Fc‐CD‐AuNCs for efficient tumor growth inhibition with minimal side effects in vivo.

Redox-Active Ferrocene Quencher-Based Supramolecular Nanomedicine for NIR-II Fluorescence-Monitored Chemodynamic Therapy.

Real-time monitoring of hydroxyl radical (⋅OH) generation is crucial for both the efficacy and safety of chemodynamic therapy (CDT). Although ⋅OH probe-integrated CDT agents can track ⋅OH production by themselves, they often require complicated synthetic procedures and suffer from self-consumption of ⋅OH. Here, we report the facile fabrication of a self-monitored chemodynamic agent (denoted as Fc-CD-AuNCs) by incorporating ferrocene (Fc) into β-cyclodextrin (CD)-functionalized gold nanoclusters (AuNCs) via host-guest molecular recognition. The water-soluble CD served not only as a capping agent to protect AuNCs but also as a macrocyclic host to encapsulate and solubilize hydrophobic Fc guest with high Fenton reactivity for in vivo CDT applications. Importantly, the encapsulated Fc inside CD possessed strong electron-donating ability to effectively quench the second near-infrared (NIR-II) fluorescence of AuNCs through photoinduced electron transfer. After internalization of Fc-CD-AuNCs by cancer cells, Fenton reaction between redox-active Fc quencher and endogenous hydrogen peroxide (H2 O2 ) caused Fc oxidation and subsequent NIR-II fluorescence recovery, which was accompanied by the formation of cytotoxic ⋅OH and therefore allowed Fc-CD-AuNCs to in situ self-report ⋅OH generation without undesired ⋅OH consumption. Such a NIR-II fluorescence-monitored CDT enabled the use of renal-clearable Fc-CD-AuNCs for efficient tumor growth inhibition with minimal side effects in vivo.

Enhanced Sulfate Formation from Gas-Phase SO2 Oxidation in Non–•OH–Radical Environments

Recent research on atmospheric particle formation has shown substantial discrepancies between observed and modeled atmospheric sulfate levels. This is because models mostly consider sulfate originating from SO2 oxidation by •OH radicals in mechanisms catalyzed by solar radiation while ignoring other pathways of non-radical SO2 oxidation that would substantially alter atmospheric sulfate levels. Herein, we use high-level quantum chemical calculations based on density functional theory and coupled cluster theory to show that monoethanolamine (MEA), a typical alkanolamine pollutant released from CO2 capture technology, can facilitate the conversion of atmospheric SO2 to sulfate in a non–•OH–radical oxidation mechanism. The initial process is the MEA-induced SO2 hydrolysis leading to the formation of HOSO2−•MEAH+. The latter entity is thereafter oxidized by ozone (O3) and nitrogen dioxide (NO2) to form HSO4−•MEAH+, which is an identified stabilizing entity in sulfate-based aerosol formation. Results show that the HOSO2−•MEAH+ reaction with O3 is kinetically and thermodynamically more feasible than the reaction with NO2. The presence of an additional water molecule further promotes the HOSO2−•MEAH+ reaction with O3, which occurs in a barrierless process, while it instead favors HONO formation in the reaction with NO2. The investigated pathway highlights the potential role alkanolamines may play in SO2 oxidation to sulfate, especially under conditions that are not favorable for •OH production, thereby providing an alternative sulfate source for aerosol modeling. The studied mechanism is not only relevant to sulfate formation and may effectively compete with reactions with sulfur dioxide and hydroxyl radicals under heavily polluted and highly humid conditions such as haze events, but also an important pathway in MEA removal processes.

Real-time investigation of reactive oxygen species and radicals evolved from operating Fe-N-C electrocatalysts during the ORR: potential dependence, impact on degradation, and structural comparisons.

Improving the stability of platinum-group-metal-free (PGM-free) catalysts is a critical roadblock to the development of economically feasible energy storage and conversion technologies. Fe-N-C catalysts, the most promising class of PGM-free catalysts, suffer from rapid degradation. The generation of reactive oxygen species (ROS) during the oxygen reduction reaction (ORR) has been proposed as a central cause of this loss of activity. However, there is insufficient understanding of the generation and dynamics of ROS under catalytic conditions due to the difficulty of detecting and quantifying short-lived ROS such as the hydroxyl radical, OH˙. To accomplish this, we use operando scanning electrochemical microscopy (SECM) to probe the production of radicals by a commercial pyrolyzed Fe-N-C catalyst in real-time using a redox-active spin trap methodology. SECM showed the monotonic production of OH˙ which followed the ORR activity. Our results were thoroughly backed using electron spin resonance confirmation to show that the hydroxyl radical is the dominant radical species produced. Furthermore, OH˙ and H2O2 production followed distinct trends. ROS studied as a function of catalyst degradation also showed a decreased production, suggesting its relation to the catalytic activity of the sample. The structural origins of ROS production were also probed using model systems such as iron phthalocyanine (FePc) and Fe3O4 nanoparticles, both of which showed significant generation of OH˙ during the ORR. These results provide a comprehensive insight into the critical, yet under-studied, aspects of the production and effects of ROS on electrocatalytic systems and open the door for further mechanistic and kinetic investigation using SECM.

Evaluating the secondary contribution of photosensitized chemistry to OH production in aerosols

Evaluating the secondary contribution of photosensitized chemistry to OH production in aerosols

Treatment of metronidazole pharmaceutical wastewater using pulsed switching peroxi-coagulation combined with electro-Fenton process

The aim of this study was to investigate the metronidazole (MNZ) degradation and real MNZ pharmaceutical wastewater treatment in the pulsed switching peroxi-coagulation (PSPC) process. Different pulsed switching frequencies and running times of H2O2 and Fe2+ productions were tested in the PSPC process. Results demonstrated that MNZ removal of 96.9 ± 1.2 % was realized in the PSPC process with a 200 mg/L MNZ and 0.1 M Na2SO4 solution within 80 min under a pulsed switching frequency of 6s: 1s and a current density of 20 mA/cm2 (H2O2) and 20 mA/cm2 (Fe2+). High MNZ removal could be attributed to efficient •OH production with the highest •OH concentration reached 321 ± 15 μM in the PSPC process. The hydroxyl and carboxyl groups of MNZ were sequentially oxidated by •OH and mineralized based on seven identified intermediates during the MNZ degradation. However, only 56.9 ± 6.7 % of COD was removed in the real MNZ wastewater treatment by the PSPC process within 90 min. A PSPC combined with electro-Fenton (EF) process was developed to enhance the COD removal in the MNZ wastewater. With MNZ wastewater as electrolytes, 3.3 ± 0.3 g/L of H2O2 was produced in a conventional EF reactor. The final COD removal reached 86–90 % using the mixture of effluent from the PSPC, the anode, and cathode chambers of the EF reactor, resulting in less than 80 mg/L COD in the effluent. Results from this study should provide a useful way to enhance real MNZ pharmaceutical wastewater treatment.

Vibrational spectroscopy and dissociation dynamics of cyclohexyl hydroperoxide.

Organic hydroperoxides (ROOH) are ubiquitous in the atmospheric oxidation of volatile organic compounds (VOCs) as well as in low-temperature oxidation of hydrocarbon fuels. The present work focuses on a prototypical cyclic hydroperoxide, cyclohexyl hydroperoxide (CHHP). The overtone OH stretch (2νOH) spectrum of jet-cooled CHHP is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of the resulting OH products. A distinctive IR feature is observed at 7012.5 cm-1. Two conformers of CHHP are predicted to have similar stabilities (within 0.2 kcal mol-1) and overtone OH stretch transitions (2νOH), yet are separated by a significant interconversion barrier. The IR power dependence indicates that absorption of three or more IR photons is required for dissociation of CHHP to cyclohexoxy (RO) and OH radical products. Accompanying high-level single- and multi-reference electronic structure calculations quantitatively support the experimental results. Calculations are extended to a range of organic hydroperoxides to examine trends in bond dissociation energies associated with RO + OH formation and compared with prior theoretical results.

Enhancing lithium-ion battery safety: Investigating the flame-retardant efficacy of bis(2,2,2-trifluoroethyl) carbonate during ethyl methyl carbonate combustion

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a candidate fire suppressant for lithium-ion batteries (LIBs). The high flammability of the electrolyte is the reason behind the frequent fire incidents reported with LIBs. These incidents are due to various factors, such as a default in the conception of the battery or operational abuse. The flame-retardant effectiveness of BtFEC was investigated by measuring its effect on the oxidation of ethyl methyl carbonate (EMC), a common LIB electrolyte component. Laminar flame speed (LFS) measurements for EMC-BtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (ϕ) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at ϕ = 1.1 with BtFEC addition ranging from 0.1 up to 1.4 % vol. To further understand the combustion chemistry of the EMC-BtFEC system, ignition delay times (time at the maximum peak production of the excited radical OH*) and CO time histories were measured in a shock tube with temperatures ranging from 1217 to 1732 K, at near-atmospheric pressure (1.24–1.42 atm), and for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0). These new results constitute an experimental database that was used to evaluate the performance of a model assembled for both BtFEC and EMC using previous work from our group. The updated, detailed chemical kinetics mechanism presented in this study consists of 237 species and 1630 reactions. Sensitivity, rate-of-production, and reaction pathway analyses permitted the oxidation of the BtFEC-EMC system to be described. A flame sensitivity analysis exhibited the significant effect from the reactions H + CF2O ⇆ HF + CFO and CF3 + H ⇆ CF2 + HF, which consume H radicals that are involved in the branching reaction H + O2⇆ OH + O, ultimately reducing the LFS. This study shows that improvements in the base fluorine chemistry are still necessary to obtain better agreement with the experiments, especially at the speciation level.

Unraveling Ros Conversion Through Enhanced Enzyme-Like Activity with Copper-Doped Cerium Oxide for Tumor Nanocatalytic Therapy.

Nanozyme catalytic therapy for cancer treatments has become one of the heated topics, and the therapeutic efficacy is highly correlated with their catalytic efficiency. In this work, three copper-doped CeO2 supports with various structures as well as crystal facets are developed to realize dual enzyme-mimic catalytic activities, that is superoxide dismutase (SOD) to reduce superoxide radicals to H2 O2 and peroxidase (POD) to transform H2 O2 to ∙OH. The wire-shaped CeO2 /Cu-W has the richest surface oxygen vacancies, and a low level of oxygen vacancy (Vo) formation energy, which allows for the elimination of intracellular reactive oxygen spieces (ROS) and continuous transformation to ∙OH with cascade reaction. Moreover, the wire-shaped CeO2 /Cu-W displays the highest toxic ∙OH production capacity in an acidic intracellular environment, inducing breast cancer cell death and pro-apoptotic autophagy. Therefore, wire-shaped CeO2 /Cu nanoparticles as an artificial enzyme system can have great potential in the intervention of intracellular ROS in cancer cells, achieving efficacious nanocatalytic therapy.

Insights into the Enhanced Photogeneration of Hydroxyl Radicals from Chlorinated Dissolved Organic Matter.

Free available chlorine has been and is being applied in global water treatment and readily reacts with dissolved organic matter (DOM) in aquatic environments, leading to the formation of chlorinated products. Chlorination enhances the photoreactivity of DOM, but the influence of chlorinated compounds on the photogeneration of hydroxyl radicals (•OH) has remained unexplored. In this study, a range of chlorinated carboxylate-substituted phenolic model compounds were employed to assess their •OH photogeneration capabilities. These compounds demonstrated a substantial capacity for •OH production, exhibiting quantum yields of 0.1-5.9 × 10-3 through direct photolysis under 305 nm and 0.2-9.5 × 10-3 through a triplet sensitizer (4-benzoylbenzoic acid)-inducing reaction under 365 nm LED irradiation. Moreover, the chlorinated compounds exhibited higher light absorption and •OH quantum yields compared to those of their unchlorinated counterparts. The •OH photogeneration capacity of these compounds exhibited a positive correlation with their triplet state one-electron oxidation potentials. Molecular-level compositional analysis revealed that aromatic structures rich in hydroxyl and carboxyl groups (e.g., O/C > 0.5 with H/C < 1.5) within DOM serve as crucial sources of •OH, and chlorination of these compounds significantly enhances their capacity to generate •OH upon irradiation. This study provides novel insights into the enhanced photogeneration of •OH from chlorinated DOM, which is helpful for understanding the fate of trace pollutants in chlorinated waters.

Surface structure regulation of sulfidated zero-valent iron by H2O2 for efficient pH self-regulation and proton cycle to boost heterogeneous Fenton-like reaction for pollutant control

Sulfidated zero-valent iron (SZVI) has been widely used in controlling organic pollutants. However, the significant decrease in catalytic activity of SZVI-based Fenton-like systems under neutral and alkaline conditions remains a large problem. Herein, it was found that surface structure regulation of SZVI with H2O2 (HT-SZVI) greatly enhanced its reactivity and efficiently activated H2O2 to oxidize various organics in a wide pH range. The HT-SZVI/H2O2 system exhibited a pH self-regulation capability that stabilized the eventual solution pH at ∼3.5 at the initial pH of 3.0–9.0. The excellent oxidation performance was primarily attributed to surface-bound •OH produced from H2O2 activation by surface Fe(II) sites on HT-SZVI. Additionally, dissolved Fe(II) converted from surface Fe(II) induced proton generation to self-regulate pH. Newly formed high proton-conductive FeS and Fe3O4 shells accelerated the transfer of accumulated protons in solution to iron core to produce Fe(II), enabling efficient proton consumption-regeneration cycle and enhancing •OH production.

Microwave-mediated ultrafast solid-state construction of O vacancies enriched cobalt oxide/nitrogen carbon aerogel toward efficient tetracycline degradation with peroxymonosulfate

A rapid microwave assisted carbonization of dicyandiamide and cobalt nitrate was developed for the first time to prepare cobalt oxide/nitrogen carbon aerogel materials, in which cobalt oxide species were uniformly loaded with the characteristics of multivalent Co species. Moreover, the rapid heating process introduced abundant oxygen vacancies and N containing heterocycles in Co@NC3A materials. The optimal Co@NC3A exhibited complete TC degradation within 10 min with a rate constant up to 0.8609 min−1 at 25 °C. Meanwhile, the Co@NC3A also had general applicability in various antibiotics and dyes degradation. Radical quenching experiment and EPR test revealed the coexistence of radical and non-radical activation process in Co@NC3A/PMS system. Multivalent Co species could activate PMS to facilitate the SO4•- and •OH production. In addition, 1O2 and direct electron transfer mediated non-radical pathways were accelerated with O vacancies and N containing heterocycle.

Pyrolysis temperature matters: Biochar-derived dissolved organic matter modulates aging behavior and biotoxicity of microplastics

Microplastics (MPs) have emerged as a novel and highly concerning contaminant that is ubiquitous in the aqueous environment. However, the aging of MPs induced by dissolved organic matter (DOM), especially biochar-derived dissolved organic matter (BDOM), and the biological toxicity after aging are not fully understood. In this study, the effects of biochar-derived BDOMs on the photoaging and biotoxicity of MPs were investigated at different pyrolysis temperatures using micro-scale polyethylene (PE) as an example. The results showed that the amount of ·OH generated by the BDOM/PE systems was related to the molecular composition and structure of BDOMs. High temperature BDOM7/9 with less lignin-like (34.33 % / 41.80 %) and more lipid (24.58 % / 19.88 %) content could produce more ·OH by itself, and its binding ability with PE was weaker due to its less hydrophobic components (SUVA260 = 0.10 / 0.11), which resulted in a weaker shading effect and less inhibition of the system, thus resulting in more ·OH production in the high temperature BDOM7/9/PE system. However, the involvement of BDOM, although favoring the long-term stable ·OH production of the system, did not significantly promote the photoaging of MPs. Furthermore, combined in vivo and in vitro biotoxicity studies of MPs showed that photoaging PE with the involvement of BDOM greatly improved systemic inflammation and tissue damage, as well as reactive oxygen species (ROS, such as ·OH and -OH)-induced cell death. For example, the addition of BDOM5/PE-light reduced the cell death of human lung, liver, and kidney cells from 54.70 %, 69.39 %, and 48.35 % to 22.78 %, 33.13 %, and 25.83 %, respectively, compared to the PE-light group. The results of this study contribute to an in-depth understanding of the environmental behavior of BDOM and MPs systems.

Unexpected hydroxyl radical production in brewed tea under sunlight.

Tea is one of the world's most popular and widely consumed beverages. It is a common pastime to enjoy a cup of tea in the sunshine. However, little attention has been given to understanding the possible photochemical reactions occurring beneath the calm surface of brewed tea. Epigallocatechin gallate (EGCG), which is widely used in food and beverages, is the most significant active ingredient found in tea. In this study, we investigated the presence of free radicals in both an aqueous EGCG solution and brewed tea under simulated sunlight conditions. To our surprise, we unexpectedly observed the production of hydroxyl radicals (•OH) in brewed tea. It was found that sunlight irradiation played a critical role in the formation of •OH, independent of the presence of metal ions. Furthermore, we demonstrated that the •OH generated from the EGCG aqueous solution induced cell cytotoxicity and DNA damage in vitro. Considering the crucial role of •OH in various fields, including human health and the environment, it is important to further explore the practical implications of •OH production in brewed tea under sunlight. In summary, our study unveils the unexpected formation of •OH in brewed tea and emphasizes the significance of sunlight-induced reactions. The observed cytotoxic and DNA-damaging effects of •OH emphasize the importance of understanding the potential health consequences associated with tea consumption. Further research in this area will contribute to a better understanding of the broader implications of •OH production in brewed tea under sunlight.

Contaminant degradation by •OH during sediment oxygenation: Effect of abundant solid matrix in aquifer

Aquifer oxygenation for hydroxyl radical (•OH) production has been recently proposed as a promising strategy for in-situ remediation. However, the high performance of this process was justified at low solid-to-liquid ratios (SLRs) of suspension systems. It remains unclear whether and how the performance is affected by abundant solid matrixes. Here we assessed the influence of SLR on •OH production and contaminant degradation during sediment oxygenation. Cumulative •OH increased from 21.8 to 165.2 μM when the SLR increased from 200 to 1600 g/L, while phenol degradation increased with the increase in SRL at the values lower than 1200 g/L and decreased at higher SLRs. As the main sediment component, silica exhibited a negligible effect on •OH production and phenol degradation because of the weak adsorption towards aqueous Fe(II). Whereas, the other component, alumina, significantly inhibited •OH production and phenol degradation because it strongly adsorbed Fe(II). •OH scavenging by solid reactive matrixes was mainly responsible for the inhibition at high SLRs. The scavenging effect could be mitigated by mediating the main reactive Fe(II) species from solid-adsorbed to dissolved phase with ligand addition. Our findings are important for understanding the side reactions and optimizing the remediation performance during aquifer oxygenation.

Observational Evidence of Unknown NOx Source and Its Perturbation of Oxidative Capacity in Bermuda's Marine Boundary Layer

AbstractNitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere.

Facet-Dependent Productions of Reactive Oxygen Species from Pyrite Oxidation.

Reactive oxygen species (ROS) are widespread in nature and play central roles in numerous biogeochemical processes and pollutant dynamics. Recent studies have revealed ROS productions triggered by electron transfer from naturally abundant reduced iron minerals to oxygen. Here, we report that ROS productions from pyrite oxidation exhibit a high facet dependence. Pyrites with various facet compositions displayed distinct efficiencies in producing superoxide (O2• -), hydrogen peroxide (H2O2), and hydroxyl radical (•OH). The 48 h •OH production rates varied by 3.1-fold from 11.7 ± 0.4 to 36.2 ± 0.6 nM h-1, showing a strong correlation with the ratio of the {210} facet. Such facet dependence in ROS productions primarily stems from the different surface electron-donating capacities (2.2-8.6 mmol e- g-1) and kinetics (from 1.2 × 10-4 to 5.8 × 10-4 s-1) of various faceted pyrites. Further, the Fenton-like activity also displayed 10.1-fold variations among faceted pyrites, contributing to the facet depedence of •OH productions. The facet dependence of ROS production can greatly affect ROS-driven pollutant transformations. As a paradigm, the degradation rates of carbamazepine, phenol, and bisphenol A varied by 3.5-5.3-fold from oxidation of pyrites with different facet compositions, where the kinetics were in good agreement with the pyrite {210} facet ratio. These findings highlight the crucial role of facet composition in determining ROS production and subsequent ROS-driven reactions during iron mineral oxidation.

Severe photochemical pollution formation associated with strong HONO emissions from dew and guttation evaporation

The unknown daytime source of HONO has been extensively investigated due to unexplained atmospheric oxidation capacity and current modelling bias, especially during cold seasons. In this study, abrupt morning increases in atmospheric HONO at a rural site in the North China Plain (NCP) were observed almost on daily basis, which were closely linked to simultaneous rises in atmospheric water vapor content and NH3 concentrations. Dew and guttation water formation was frequently observed on wheat leaves, from which water samples were taken and chemically analyzed for the first time. Results confirmed that such natural processes likely governed the daily nighttime deposition and daytime release of HONO and NH3, which have not been considered in the numerous HONO budget studies investigating its large missing daytime source in the NCP. The dissolved HONO and NH3 in leaf surface water droplets reached 1.4 and 23 mg L−1 during the morning on average, resulting in averaged atmospheric HONO and NH3 increases of 0.89 ± 0.61 and 43.7 ± 29.3 ppb during morning hours, with relative increases of 186 ± 212 % and 233 ± 252 %, respectively. The high atmospheric oxidation capacity contained within HONO was stored in near surface liquid water (such as dew, guttation and soil surface water) during nighttime, which prevented its atmospheric dispersion after sunset and protected it from photodissociation during early morning hours. HONO was released in a blast during later hours with stronger solar radiation, which triggered and then accelerated daytime photochemistry through the rapid photolysis of HONO and subsequent OH production, especially under high RH conditions, forming severe secondary gaseous and particulate pollution. Results of this study demonstrate that global ecosystems might play significant roles in atmospheric photochemistry through nighttime dew formation and guttation processes.