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• The ratio between OH production from HONO and from (HONO+O3) lager than 90% before 12:00. • The source of HONO from combustion emission is ~26%. • NO 2 being converted to HONO under the conditions with high aerosol extinction coefficient and high relative humidity was a dominant factor for the secondary produce of HONO. • HONO mainly distributed near the surface and localized, and NO 2 mainly transmitted from north at ~ 0.6 km. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations were operated from 02 to 21 December 2018 in Leshan, southwest China, to measure HONO, NO 2 and aerosol extinction vertical distributions, and these were the first MAX-DOAS measurement results in Sichuan Basin. During the measurement period, characteristic ranges for surface concentration were found to be 0.26–4.58 km−1 and averaged at 0.93 km−1 for aerosol extinction, 0.49 to 35.2 ppb and averaged at 4.57 ppb for NO 2 and 0.03 to 7.38 ppb and averaged at 1.05 ppb for HONO. Moreover, vertical profiles of aerosol, NO 2 and HONO were retrieved from MAX-DOAS measurements using the Heidelberg Profile (HEIPRO) algorithm. By analysing the vertical gradients of pollutants and meteorological information, we found that aerosol and HONO are strongly localised, while NO 2 is mainly transmitted from the north direction (city center direction). Nitrogen oxides such as HONO and NO 2 are important for the production of hydroxyl radical (OH) and oxidative capacity in the troposphere. In this study, the averaged value of OH production rate from HONO is about 0.63 ppb/hr and maximum value of ratio between OH production from HONO and from (HONO+O 3) is > 93% before12:00 in Leshan. In addition, combustion emission contributes to 26% for the source of HONO in Leshan, and we found that more NO 2 being converted to HONO under the conditions with high aerosol extinction coefficient and high relative humidity is also a dominant factor for the secondary produce of HONO. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced H 2 O 2 productivity on the hydrophobic modified gas diffusion electrode. • Enhanced pollutant removal by combining electro-Fenton with anodic oxidation (EF+AO). • The EF+AO process exhibits good universality and high stability. • Treating actual refinery wastewater with a low energy consumption. To boost refractory pollutant removal over a broad pH range, we here proposed an integrated electrocatalytic process combining electrochemical anodic oxidation (AO) with cathodic electro-Fenton (EF) based on a hydrophobic modified gas diffusion electrode and heterogeneous Fenton catalyst of FeOCl. Total organic carbon (TOC) removal of refractory levofloxacin by EF + AO process was 85% in 120 min under the applied potential of −0.6 V and pH ∼6.7, obviously higher than that of only AO (22%) or EF (62%) process. Significantly, EF+AO process was demonstrated to be efficient and stable for actual wastewater treatment that chemical oxygen demand (COD) value of refinery wastewater after EF + AO treatment was steadily met the discharge standard (GB 18918–2002) for sewage treatment plants in China (I-A: COD < 50 mg/L) during 100 h of consecutive runs. Our results provide new insights into developing an energy-efficient electrocatalytic technology for enhancing refractory pollutant removal. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO) can be photolyzed to produce hydroxyl radicals (OH) in the atmosphere. OH plays a critical role in the formation of secondary pollutants like ozone (O 3 ) and secondary organic aerosols (SOA) via various oxidation reactions. Despite the abundance of recent HONO studies, research on national HONO emissions in China remains relatively limited. Therefore, this study employed a "wetting-drying" model and bottom-up approach to develop a high-resolution gridded inventory of HONO emissions for mainland China using multiple data. We used the Monte Carlo method to estimate the uncertainty in HONO emissions. In addition, the primary sources of HONO emissions were identified and their spatiotemporal distribution and main influencing factors were studied. The results indicated that the total HONO emissions in mainland China in 2016 were 0.77 Tg N (R 50 : 0.28-1.42 Tg N), with soil (0.42 Tg N) and fertilization (0.26 Tg N) as the primary sources, jointly contributing to over 87% of the total. Notably, the North China Plain (NCP) had the highest HONO emission density (3.51 kg N/ha/yr). Seasonal HONO emissions followed the order: summer (0.38 kg N/ha) > spring (0.19 kg N/ha) > autumn (0.17 kg N/ha) > winter (0.06 kg N/ha). Moreover, HONO emissions were strongly correlated with fertilization, cropland, temperature, and precipitation. This study provides vital scientific groundwork for the atmospheric nitrogen cycle and the formation of secondary pollutants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

[Display omitted] • Scaling up preparation of modified catalysts by direct calcination in air. • Both defects and oxygen-containing groups contribute to performance enhancement. • Electro-Fenton for high pollutant removal kinetics in a wide pH range. • Industrializable case of 30 g catalyst synthesis theoretically for 5.4 m2 electrode. • Lab-scale demonstration for wastewater treatment with capacity of 7.2 L/h. Electro-Fenton (EF) regarded as a green substitution to traditional homogeneous Fenton, produces highly oxidizing OH through in-situ H 2 O 2 electrosynthesis and electrochemical Fe2+ regeneration. One of obstacles that hinders translation of bench-scale EF performance to water treatment practices is the difficulty of scaling up catalyst/electrode preparation in low cost while producing high performance. Here we report scalable preparation of modified carbon catalysts for high-efficiency EF by directly calcinating commercial carbonaceous materials in air. The EF with modified carbon cathode shows high kinetics of 0.296–0.569 min−1 for levofloxacin removal in much wider pH range of 3.0–6.6 using less Fe dosage compared with homogeneous Fenton. This EF system can reduce chemical oxygen demand (COD) of coking wastewater from 312.0 to 99.5 mg L−1 to satisfy wastewater discharge standard in China while consuming low electricity of 1.8–4.9 kWh kg−1 COD−1. We demonstrated the scalability of this EF process by scaling up preparative throughput of catalyst (30 g that can be processed into electrodes with total working areas of 54000 cm2), enlarging electrode size (230 cm−2) and reactor volume with wastewater treatment capacity of 7.2 L/h. This scalability demonstration of EF technology shows the promising potential of achieving low-cost advanced wastewater treatment. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5 ) is a major air pollutant in most cities of China, and poses great health risks to local residents. In this study, the health effects of PM 2.5 in Nanjing and Yangzhou were compared using computational and experimental methods. The global exposure mortality model (GEMM), including the results of a cohort study in China, was used to estimate the disease-related risks. Premature mortality attributable to PM 2.5 exposure were markedly higher in Nanjing than that in Yangzhou at comparable levels of PM 2.5 (8191 95% CI, 6975-9994 vs. 6548 95% CI, 5599-8049 in 2015). However, the baseline mortality rate was on a country-level and the age distribution was on a province-level, traditional estimation method could not accurately represent the health burdens of PM 2.5 on a city-level. We proposed a refined calculation method which based on the actual deaths of each city and the disease death rates. Conversely, similar concentrations of PM 2.5 exposure resulted in higher actual deaths per million population in Yangzhou (1466 95% CI, 1266-1746) than that in Nanjing (1271 95% CI, 1098-1514). Health risks of PM 2.5 are associated with the generation of reactive oxygen species, among which hydroxyl radial (·OH) is the most reactive one. We then collected these PM 2.5 samples and quantified the induced ·OH. Consistently, average ·OH concentration in 2015 was higher in Yangzhou than that in Nanjing, again indicating that PM 2.5 in Yangzhou was more toxic. The combination of computational and experimental methods demonstrated the complex relationship between health risks and PM 2.5 concentrations. The refined estimation method could help us better estimate and interpret the risks caused by PM 2.5 exposure on a city-level., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The concentration of advanced glycation end products (AGEs) in foods, which are formed by Maillard reaction, has demonstrated as risk factors associated with many chronic diseases. The AGEs inhibitory activities of five common phenolic acids (protocatechuic acid, dihydroferulic acid,p-coumaric acid,p-hydroxybenzoic acid and salicylic acid) with different chemical properties had been investigated in two food simulation systems (glucose-bovine serum albumin (BSA) and oleic acid-BSA). The results substantiated that the AGEs inhibitory abilities of phenolic acids in the oleic acid BSA system were much better than the glucose-BSA system for their strong reducing powers and structures. Among them, dihydrogenferulic acid showed strong inhibition of AGEs formation in oleic acid-BSA system at 0.01 mg/mL compared to nonsignificant AGEs inhibitory effect in oleic acid-BSA system at 10-fold higher concentration (0.1 mg/mL). This study suggests that edible plants rich in phenolic acids may be used as AGEs inhibitor during high-fat cooking. [ABSTRACT FROM PUBLISHER]

Reactive oxygen species (ROS) play a central role in health effects of ambient fine particulate matter (PM 2.5 ). In this work, we screened for efficient and complementary oxidative potential (OP) measurements by comparing the response values of multiple chemical probes (OP DTT , OP OH , OP GSH ) to ambient PM 2.5 in Shenzhen, China. Combined with meteorological condition and PM 2.5 chemical composition analysis, we explored the effects of different chemical components and emission sources on the ambient PM 2.5 OP and analyzed their seasonal variations. The results show that OP m DTT (mass-normalized) and OP m GSH-SLF were highly correlated (r = 0.77). OP DTT was mainly influenced by organic carbon, while OP OH was highly dominated by heavy metals. The combination of OP DTT and OP OH provides an efficient and comprehensive measurement of OP. Temporally, the OPs were substantially higher in winter than in summer (1.4 and 4 times higher for OP m DTT and OP m OH , respectively). The long-distance transported biomass burning sources from the north dominated the OP DTT in winter, while the ship emissions mainly influenced the summer OP. The OP m DTT increased sharply with the decrease of PM 2.5 mass concentration, especially when the PM 2.5 concentration was lower than 30 μg/m 3 . The huge differences in wind fields between the winter and summer cause considerable variations in PM 2.5 concentrations, components, and OP. Our work emphasizes the necessity of long-term, multi-method, multi-component assessment of the OP of PM 2.5 ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Atmospheric oxidizing capacity (AOC) is the fundamental driving factors of chemistry process (e.g., the formation of ozone (O 3 ) and secondary organic aerosols (SOA)) in the troposphere. However, accurate quantification of AOC still remains uncertainty. In this study, a comprehensive field campaign was conducted during autumn 2019 in downtown of Beijing, where O 3 and PM 2.5 episodes had been experienced successively. The observation-based model (OBM) is used to quantify the AOC at O 3 and PM 2.5 episodes. The strong intensity of AOC is found at O 3 and PM 2.5 episodes, and hydroxyl radical (OH) is the dominating daytime oxidant for both episodes. The photolysis of O 3 is main source of OH at O 3 episode; the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) plays important role in OH formation at PM 2.5 episode. The radicals loss routines vary according to precursor pollutants, resulting in different types of air pollution. O 3 budgets and sensitivity analysis indicates that O 3 production is transition regime (both VOC and NO x -limited) at O 3 episode. The heterogeneous reaction of hydroperoxy radicals (HO 2 ) on aerosol surfaces has significant influence on OH and O 3 production rates. The HO 2 uptake coefficient (γHO 2 ) is the determining factor and required accurate measurement in real atmospheric environment. Our findings could provide the important bases for coordinated control of PM 2.5 and O 3 pollution., (Copyright © 2021. Published by Elsevier B.V.)

Reactive oxygen species (ROS) induced by particulate matter (PM), of which •OH is the most active free radical, have adverse health effects; however, PM-induced generation of ROS and •OH has not been quantified and studied in northwest China, which suffers from severe dust storms. In this study, ambient PM 10 and PM 2.5 collected from the urban area of Hotan in the Uygur Autonomous Region of China, during dust and non-sand periods in 2020. ROS and •OH were quantified and examined using the dichlorofluorescein diacetate (DCFH) assay and fluorescent probe method. The results showed that the oxidation potential (OP) of PM in the non-dust period (PM 2.5 : 7.77 ± 0.29 nmol H 2 O 2 m−3; PM 10 : 8.9 ± 0.38 nmol H 2 O 2 m−3) was higher than in the dust period (PM 2.5 : 1.14 ± 0.71 nmol H 2 O 2 m−3; PM 10 : 1.85 ± 0.77 nmol H 2 O 2 m−3). Compared to PM 10 , PM 2.5 with larger specific surface area is more likely to adsorb the components contributing to ROS generation, so the induction amount of ROS and •OH per unit volume in the environment will increase with increasing PM 2.5 concentration. There was a weak correlation between O 3 and ROS concentrations in the PM during the day, suggesting that photochemical reactions were a moderating factor in the formation of daytime ROS. In PM 2.5 , ROS showed a weak correlation with Pb, Cu, and Fe during the dust period. During the non-dust period, significantly correlated with Fe, Cu, and Cd (P < 0.01; P < 0.05). In PM 10 , ROS correlated significantly with As (P < 0.05) but weakly with Fe and Pb during the dust period. During the non-dust period, significantly correlated with As and Cd (P < 0.01; P < 0.05) and weakly correlated with Ni, Cu, and Fe. This indicates that increasing trace metal levels can increase the OP of atmospheric PM. • The oxidation potential in the non-sand period was higher than that in the dust period. • Oxidation potential per unit volume: PM 10 >PM 2.5 • Photochemical reactions were a moderating factor in the formation of daytime ROS. • The metals in the particles were beneficial for increasing the oxidation potential. [ABSTRACT FROM AUTHOR]

In order to study methane degradation and the kinetic law with hydroxyl radicals (• OH) generated via Fen-ton reagent,in the self-designed bubbling reactor,the effects of reaction time, H2O2 concentration, Fe2+ concentration, initial pH value,and reaction temperature on coal-mine gas( methane)removal efficiency were investigated respectively. The experimental results indicate that Fenton reagent can effectively decompose methane. As for methane with an initial concentration of 4. 9%, about 0. 25 of methane is degraded under the optimized experimental conditions of c(H2O2)= 100 mmol/L, c ( Fe2+ ) = 2. 0 mmol/L, initial pH value of 2. 5, and reaction temperature 25 °C after 30 min. Furthermore, the non-linear fitting of relationship curves between the degradation efficiency of methane and reaction time, demonstrates that the reaction kinetics accorded with Boltzmann equation. Meanwhile, the parameter dx acts as the concentration empirical correction-factor of influencing the degradation efficiency of methane and the quantitative calculation-formula of methane degradation rate is finally obtained. [ABSTRACT FROM AUTHOR]

Abstract: The atmospheric concentrations of nitrous acid (HONO) have been measured during two field campaigns in the winter and summer of 2007 at Beijing (China). The results were discussed from the standpoint of temporal and diurnal variations and meteorological effects. The daily average HONO concentrations were in the range of 0.03–2.91ppb and didn''t show temporal variation between the winter and summer periods. The temporal trends seemed to be largely affected by meteorological conditions. HONO concentrations showed very typical diurnal variations during intensive winter and summer periods. Nitrogen oxides were key precursors of HONO formation and the HONO/NO2 values were higher than those reported for direct emission (<1%), indicating the prevalence of secondary chemical HONO formation on direct emission during both periods. We used a pseudo steady state approach (PSS), which included homogeneous and heterogeneous reactions and direct emission, explaining on average about 83% and 48% of the observed HONO levels during the intensive winter and summer periods, respectively. The daytime unknown HONO production was on average 2.58ppbh−1 during the summer period. The HNO3 and fine particulate NO3 − photolysis contributed weakly as HONO source. Including these sources in the PSS calculation, we explained about 53% of the observed HONO levels. The results showed that heterogeneous JNO2 dependent processes on aerosol and ground surfaces, involving NO2 as HONO precursor, were HONO sources during the summer measurements. [Copyright &y& Elsevier]

With an Xe arc lamp house as simulated sunlight, the influences of fulvic acid (FA) concentration and origins on photodegradation of acenaphthene, fluorine, phenanthrene, fluoranthene and pyrene in aqueous solution have been studied. Similar effects of FAs, collected from five places around China, on polycyclic aromatic hydrocarbon (PAH) photodegradation have been observed. Active oxygen was of significance in PAH photodegradation with the presence of FAs. For systems with 1.25mgL−1 FAs, the contributions of photodegradation rates were from 33% to 69%. FAs had two opposite effects, i.e., stimulating the generation of active oxygen and advancing PAH photodegradation; competing with PAHs for energy and photons and restraining PAH photodegradation. Generally, photodegradation rates of the 5 PAHs decreased with the increase of FAs concentration; except fluoranthene and pyrene were advanced in solutions with low FA concentration. The influences of FA concentration on PAH photodegradation were more significant than FA origin. [Copyright &y& Elsevier]

Short-chain chlorinated paraffins (SCCPs) are a complex mixture of polychlorinated alkanes (C 10 -C 13 , chlorine content 40-70%), and have been categorized as persistent organic pollutants. However, there are knowledge gaps about their environmental degradation, particularly the effectiveness and mechanism of photochemical degradation in surface waters. Photochemically-produced hydrated electrons (e - (aq) ) have been shown to degrade highly chlorinated compounds in environmentally-relevant conditions more effectively than hydroxyl radicals (·OH), which can degrade a wide range of organic pollutants. This study aimed to evaluate the potential for e - (aq) and ·OH to degrade SCCPs. To this end, the degradation of SCCP model compounds was investigated under laboratory conditions that photochemically produced e - (aq) or ·OH. Resulting SCCP degradation rate constants for e - (aq) were on the same order of magnitude as well-known chlorinated pesticides. Experiments in the presence of ·OH yielded similar or higher second-order rate constants. Trends in e - (aq) and ·OH degradation rate constants of the investigated SCCPs were consistent with those of other chlorinated compounds, with higher chlorine content producing in higher rate constants for e - (aq) and lower for ·OH. Above a chlorine:carbon ratio of approximately 0.6, the e - (aq) second-order rate constants were higher than rate constants for ·OH reactions. Results of this study furthermore suggest that SCCPs are likely susceptible to degradation in sunlit surface waters, facilitated by dissolved organic matter as a source of photochemically produced e - (aq) and ·OH., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The formation and evolution of sulfate (SO 4 2- ) and nitrate (NO 3 ) and its chemical components in four heavy haze pollution episodes at 14 sampling sites in a severe cold climate region of Northeast China in winter from 2017 to 2019. The results yielded two main findings. (1) Nitrate formation during the day was mainly due to the combination of high emissions and high relative humidity (RH, 50-90%), high temperature (T, 0 to 5 °C), high atmospheric oxidizability (ozone (O - ) secondary contaminants under different stages of pollution episodes and different meteorological and emission conditions were compared, based on the simultaneous observation of fine particulate matter (PM 2.5 ) concentrations. Nitrate was formed by a gas-phase homogeneous reaction of the hydroxyl radical (OH·) with nitrogen dioxide (NO 3 ) and nitrous acid (HONO) concentrations), and high ammonia (NH 3 ) concentrations. Nitrate was formed by a gas-phase homogeneous reaction of the hydroxyl radical (OH·) with nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 formation between Northeast China and other regions were that the gas-phase oxidation process played an important role. This was mainly a result of the promotion of the gas-phase oxidation of SO 3 ). (2) The main differences in SO 4 2- formation between Northeast China and other regions were that the gas-phase oxidation process played an important role. This was mainly a result of the promotion of the gas-phase oxidation of SO 4 2- due to the high oxidizing ability and the suppression of the aqueous reaction due to the low Ts in winter and low-sulfur coal emissions. Sulfate formation mostly occurred through an aqueous phase reaction in winter, but the highest yield and the fastest production capacity were produced by the gas-phase reaction., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

[Display omitted] • Mn/UIO-66 was used in vaporized hydrogen peroxide system for toluene removal. • Toluene removal efficiency of 82% was obtained due to hydroxyl radical oxidation. • Excessive manganese decoration caused Mn/UIO-66 poor surface characteristic. • Toluene decomposed into small organic molecules and finally converted into CO 2. Gaseous toluene, one of the volatile organic compounds, has aroused wide concerns in China due to its growing emissions and harmfulness. Herein, novel manganese decorated UIO-66 catalysts (Mn/UIO-66) were prepared by hydrothermal synthesis and applied to the vaporized hydrogen peroxide system for toluene removal. TEM, BET, XRD, ICP, and XPS were used to analyze the chemical and physical characteristics of Mn/UIO-66. A toluene removal efficiency of 82% with the 3-Mn/UIO-66 catalyst in the vaporized hydrogen peroxide system could achieved. The effects of different reaction conditions (reaction temperature, hydrogen peroxide concentration, and initial toluene concentration) on toluene removal were determined. The yield of hydroxyl radical in the Mn/UIO-66 catalyst combined with the hydrogen peroxide system was positively correlated with the Mn decorated ratio. Results suggested that the catalytic performance is related not only to the yield of hydroxyl radical but also to the catalyst specific surface. The intermediate products during toluene removal were analyzed by gas chromatography-mass spectrometry (GC–MS), and the possible reaction pathway of toluene removal was proposed. [ABSTRACT FROM AUTHOR]

Atmospheric nitrous acid (HONO) is a dominant precursor of hydroxyl (OH) radicals, and its formation mechanisms are still controversial. Few studies have simultaneously explored effects of different combustion processes on HONO sources. Hereby, synchronous HONO measurement in urban (BJ), suburban (XH) and rural (DBT) areas with different combustion processes is performed in the North China Plain in winter. A box model is utilized to analyze HONO formation mechanisms. HONO concentration is the highest at the DBT site (2.51 ± 1.90 ppb), followed by the XH (2.18 ± 1.95 ppb) and BJ (1.17 ± 1.20 ppb) sites. Vehicle exhaust and coal combustion significantly contribute to nocturnal HONO at urban and rural sites, respectively. During a stagnant pollution period, the NO+OH reaction and combustion emissions are more crucial to HONO in urban and rural areas; meanwhile, the heterogeneous reaction of NO 2 is more significant in suburban areas. Moreover, the production rate of OH from HONO photolysis is about 2 orders of magnitude higher than that from ozone photolysis. Consequently, vehicle exhaust and coal combustion can effectively emit HONO, further causing environmental pollution and health risks. It is necessary to expand the implementation of the clean energy transition policy in China, especially in areas with substantial coal combustion.

Nitrous acid (HONO) can powerfully influence atmospheric photochemistry by producing hydroxyl radical (OH), which is a crucial oxidant that controls the fate of atmospheric trace species. To deduce HONO formation mechanisms in polluted regions, two field observations were conducted in urban Beijing during the early summer of 2017 and the winter of 2018. These two seasons bore distinguishing pollution characteristics with a higher degree of ageing and heavier aerosol loading in the early summer and more abundant NO x (NO x  = NO + NO 2 ) in the winter. Elevated concentrations of HONO were observed during these two seasons, with the mean ± standard deviation (maximum) concentrations of 1.25 ± 0.94 (6.69) ppbv and 1.04 ± 1.27 (9.55) ppbv in early summer and winter, respectively. The observed daytime (08:00-17:00 h, local time) HONO production rate was several times higher in early summer than in winter (4.44 ± 1.93 ppbv h -1 vs. 0.88 ± 0.49 ppbv h -1 ). Budget analysis revealed distinct daytime HONO formation mechanisms during these two seasons. Photo-induced heterogeneous conversion of NO 2 on the ground surface dominated in early summer, and homogeneous reaction of NO + OH was dominant in winter. Photolysis of HONO was the major source of primary OH in both seasons, and thus, played a key role in the regulation of atmospheric oxidising capacity. This study demonstrates the significant seasonal variations in HONO budget and underlines the predominant role of HONO in primary OH production in Beijing. Our findings will be helpful to gain an understanding of the chemical mechanisms underlying the formation of secondary pollution in metropolitan areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

• The formation and mechanism of sedimentary HO• in seasonal lake were studied. • Potential of HO• exhibited high spatial heterogeneities from 3.75 to 271.8 μmol kg−1. • Sedimentary Fe-smectite was the key Fe(II) species for HO• formation. • LMW-DOM exhibited higher formation potential than the bulk and HMW counterparts. • HO• yield was correlated to both the contents and the species of Fe(II) and DOM. Seasonal flooding-drought transformation process of lake sediments lead to changes of dissolved oxygen and redox conditions and the resultant generation of hydroxyl radical (HO•). To date, information on HO• formation and its regulators in seasonal lake sediments is largely unexplored. In this study, a total of nineteen sediments were collected from Lake Poyang, China, with the formation and mechanisms of HO• during the oxygenation process exploring via the incubation experiments, Fe K-edge X-ray adsorption spectroscopy, ultrafiltration, and fluorescent spectroscopy. Results showed that the concentrations of HO• generated ranged from 3.75 ± 1.13 to 271.8 ± 22.81 μmol kg−1, demonstrating high formation potential and obvious spatial heterogeneity. The yield of HO• formed was positively correlated with the contents of Fe(II), sedimentary organic carbon, and dissolved organic carbon, showing a general contribution of these reduced substances to HO• formation. Furthermore, application of Fe K-edge X-ray adsorption spectroscopy revealed the key species of sedimentary Fe-smectite for HO• formation due to its high peroxidase-like activity. Besides inorganic Fe(II), the sedimentary dissolved organic matters (DOMs) represented an important regulator for HO• formation, which contributed about 2–11% of the total HO• generation. Moreover, the DOM-induced formation potential was found to be highly related to the molecular weight distribution that the low molecular weight- (LMW, <1 kDa) fraction exhibited higher HO• formation potential than the bulk and high molecular weight- (HMW, 1 kDa-0.45 μm) counterparts. In addition, the omnipresent mineral Fe(II)-DOM interaction in sediment matrix exhibited another 2–6% of contribution to the total HO• production. This study highlighted the importance of contents and species of Fe(II) and DOM in manipulating the HO• yield, providing new insight into understanding the formation mechanisms of HO• in the seasonal lake sediment. [Display omitted] [ABSTRACT FROM AUTHOR]

HONO along with other trace gases and actinic flux were continuously measured in selected months from December 2015 to November 2016 near a major industrial zone of the Yangtze River Delta (YRD) region of China. The seasonalities of HONO and its formation mechanisms were explored. A box model was developed to assess the role of HONO chemistry in the atmospheric oxidative capacity in the study area. The model was constrained by in-situ observations to minimize simulation uncertainties. Our measurement results demonstrate that HONO mean concentration and diurnal profile varied noticeably between different seasons with the maximum (1.32 ± 0.92 ppbv) observed in winter, coincided with high mass loading of fine particles (PM 2.5 = 114 ± 59.6 μg m−3). The averaged nighttime NO 2 to HONO conversion ratios (hr−1) were (1.83 ± 0.73)% in spring, (2.91 ± 1.06)% in summer, (0.72 ± 0.44)% in autumn, and (0.84 ± 0.45)% in winter. The homogeneous reaction of OH + NO was responsible for a large portion of HONO production throughout the year but was relatively weaker compared to other mechanisms in winter. Heterogeneous reactions on ground surfaces were much stronger than those on aerosol surfaces, dominating nighttime HONO production, except in summer. Primary HONO emissions were only responsible for a small portion of the HONO budget. Particulate nitrate photolysis was a significant source of HONO and it showed very little variation in different seasons. OH budget analysis shows that O 3 photolysis was a major contributor to the OH production in the study area while HONO photolysis provided an extra boost to the photochemical reactivity in the early morning, particularly during summer. However, HONO chemistry played a more important role in autumn and winter by dominating OH production throughout the day. Accordingly, effective control of NO x emissions dominated by industries can significantly reduce HONO production and thus weaken the atmospheric oxidative capacity in the study area. • Seasonal HONO ranged from 0.92 ± 0.61 ppbv in spring to 1.32 ± 0.92 ppbv in winter. • Generally, heterogeneous mechanisms on ground dominated nighttime HONO formation. • HONO photolysis predominated OH production in autumn and winter. • Reduction in NO x emissions may effectively reduce HONO and haze formation in winter. [ABSTRACT FROM AUTHOR]

Hydroxyl radical (HO∙) in natural waters plays a critical role in contaminant transformation and ecosystem health. In this study, the photogeneration and steady-state concentration of HO∙ in different aquatic environments (e.g., river and lake) along the middle-lower Yangtze region, China, were evaluated. The results showed that, compared to lake samples, the river waters were characterized by lower HO∙ photoformation rate (R HO ∙) (5.10–11.69 × 10−11 vs. 1.10–1.82 × 10−10 M s−1) and steady-state HO∙ concentration ([HO∙]) (1.76–3.11 × 10−17 vs. 2.50–10.33 × 10−17 M). The contribution of nitrate and nitrite to the total R HO ∙ in river waters was generally higher than that in lake waters, and photolysis of nitrite exhibited contributions 1–2 times higher than those of nitrate (0–25% vs. 0–9%) irrespective of sample types. As a result, the photosensitization by chromophoric dissolved organic matter (CDOM) contributed more than 70% of the total R HO ∙ for all samples except for River Ganjiang. [HO∙] among all samples was positively correlated with dissolved organic carbon (DOC) concentration, and the DOC-normalized [HO∙] was further related to the physicochemical properties of CDOM samples (e.g., aromaticity, humification, and molecular weight). The humic-like aromatic substances with low molecular weight were the controlling factors influencing [HO∙] in the studied surface waters. The results contributed to a deeper understanding of behaviors and fate of aquatic DOMs in terms of HO∙ formation and contaminant attenuation. Image 1 • Abundance, source, and influencing factors of R HO ∙ and [HO∙] in contrasting waters were studied. • River waters contained generally lower R HO ∙ and [HO∙] than the lake waters. • Nitrite and nitrate contributed 0.2–24.8% and 0.1–8.8% of HO∙ formation, respectively. • DOM photosensitization contributed more than 70% of HO∙ formation for all samples except for one river water. • Both abundance and inherent properties (SUVA 254 , HIX, and molecular weight) of DOM influenced [HO∙]. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO) plays a significant role in atmospheric chemistry due to its contribution to hydroxyl radical (OH). However, no scientific consensus has been achieved about the daytime HONO formation mechanisms. To identify the seasonal variations of HONO chemistry and the impacts of biomass burning (BB), we performed a two-phased field study in winter-spring and summer (covering a harvest season) in 2017 at a rural coastal site in North China. Though the mean HONO concentration in winter-spring (0.26 ± 0.28 ppbv) was higher than in summer (0.17 ± 0.19 ppbv), the maximum HONO concentrations were comparable (~2 ppbv) in the two campaigns. Both the HONO/NO x ratio and nocturnal heterogeneous conversion efficiency of HONO (C HONO) in summer were over twice of that in winter-spring. The daytime budget analysis also revealed that the strength of P other (i.e., the HONO sources apart from the reaction of OH + NO) in summer was double of that in winter-spring. BB affected the HONO concentration by enhancing the contribution of heterogeneous HONO production on the aerosol surface but weakening the role of photo-related HONO formation. HONO photolysis was a significant source of OH in both winter-spring and summer, and its contribution could be further enhanced during the BB episode in summer. Our study demonstrates the significant seasonal variations of HONO and the effects of BB, and suggests needs for more multi-season observations and considerations of BB, especially during the harvest time, in HONO research. Image 1 • Significant seasonal variations of HONO pollution and chemistry were found. • Source strength of HONO can be enhanced by solar radiation and biomass burning. • Biomass burning enhanced the role of aerosol in heterogeneous HONO formation. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO) is a major source of hydroxyl (OH) radicals, and identifying its source is crucial to atmospheric chemistry. Here, a new formation route of HONO from the reaction of NO with Cl radicals with the aid of one or two water molecules [(Cl) (NO) (H 2 O) n ( n = 1-2)] as well as on the droplet surface was found by Born-Oppenheimer molecular dynamic simulation and metadynamic simulation. The (Cl) (NO) (H 2 O) 1 (monohydrate) system exhibited a free-energy barrier of approximately 0.95 kcal mol -1 , whereas the (Cl) (NO) (H 2 O) 2 (dihydrate) system was barrierless. For the dihydrate system and the reaction of NO with Cl radicals on the droplet surface, only one water molecule participated in the reaction and the other acted as the "solvent" molecule. The production rates of HONO suggested that the monohydrate system ([NO] = 8.56 × 10 12 molecule cm -3 , [Cl] = 8.00 × 10 6 molecule cm -3 , [H 2 O] = 5.18 × 10 17 molecule cm -3 ) could account for 40.3% of the unknown HONO production rate ( P unknown at site 2 in the East China Sea. This study identified the importance of the reaction system of NO, Cl, and water molecules in the formation of HONO in the marine boundary layer region.P unknown at site 2 in the East China Sea. This study identified the importance of the reaction system of NO, Cl, and water molecules in the formation of HONO in the marine boundary layer region.

Nitrous acid (HONO) is a major precursor of tropospheric hydroxyl radical (OH) that accelerates the formation of secondary pollutants. The HONO sources, however, are not well understood, especially in polluted areas. Based on a comprehensive winter field campaign conducted at a rural site of the North China Plain, a box model (MCM v3.3.1) was used to simulate the daytime HONO budget and nitrate formation. We found that HONO photolysis acted as the dominant source for primary OH with a contribution of more than 92%. The observed daytime HONO could be well explained by the known sources in the model. The heterogeneous conversion of NO 2 on ground surfaces and the homogeneous reaction of NO with OH were the dominant HONO sources with contributions of more than 36 and 34% to daytime HONO, respectively. The contribution from the photolysis of particle nitrate and the reactions of NO 2 on aerosol surfaces was found to be negligible in clean periods (2%) and slightly higher during polluted periods (8%). The relatively high OH levels due to fast HONO photolysis at the rural site remarkably accelerated gas-phase reactions, resulting in the fast formation of nitrate as well as other secondary pollutants in the daytime.

The oxidation of nitric oxide to nitrogen dioxide by hydroperoxy (HO 2 ) and organic peroxy radicals (RO 2 ) is responsible for the chemical net ozone production in the troposphere and for the regeneration of hydroxyl radicals, the most important oxidant in the atmosphere. In Summer 2014, a field campaign was conducted in the North China Plain, where increasingly severe ozone pollution has been experienced in the last years. Chemical conditions in the campaign were representative for this area. Radical and trace gas concentrations were measured, allowing for calculating the turnover rates of gas-phase radical reactions. Therefore, the importance of heterogeneous HO 2 uptake on aerosol could be experimentally determined. HO 2 uptake could have suppressed ozone formation at that time because of the competition with gas-phase reactions that produce ozone. The successful reduction of the aerosol load in the North China Plain in the last years could have led to a significant decrease of HO 2 loss on particles, so that ozone-forming reactions could have gained importance in the last years. However, the analysis of the measured radical budget in this campaign shows that HO 2 aerosol uptake did not impact radical chemistry for chemical conditions in 2014. Therefore, reduced HO 2 uptake on aerosol since then is likely not the reason for the increasing number of ozone pollution events in the North China Plain, contradicting conclusions made from model calculations reported in the literature.

• Fe/AC-activated H 2 O 2 oxidation achieved efficient P recovery and Ni removal. • Activated carbon promoted the generation of Fe2+ from Fe0 to improve H 2 O 2 activation. • FePO 4 from the oxidation of hypophosphite was the major phosphate in the residue. • P recovery in wastewater led to a low P concentration below the discharge limitation. • Simultaneous Ni removal was achieved via Ni complex decomposition. The recovery of phosphorus (P) from wastewater has attracted substantial attention with the atrophy of global P resource. In the current work, the simultaneous recovery of P with the removal of nickel (Ni) via iron/activated carbon (Fe/AC) and hydrogen peroxide (H 2 O 2) form nickel-plating wastewater was achieved. The isotherm reaction showed a maximum P recovery of 99.99% with an equilibrium concentration of P of 0.12 mg/L, which was lower than the limitation of discharge regulation (China national regulation, 0.5 mg/L). The optimal conditions for P recovery were 0.25 mol/L H 2 O 2 , a Fe/AC mass ratio of 1:1, an at 60 °C, which led to the ratio of P in the form of FePO 4 in the residue to be 77%. Moreover, the Fe/AC microelectrolysis coupling to H 2 O 2 promoted Fe2+ production from Fe0 and improved the circulation of Fe2+, which improved the production of hydroxyl radicals with increasing pH and consequently enhanced oxidation efficiency of hypophosphite. The FePO 4 was found the major form of phosphate in the precipitate. The highest removal rate of nickel was 89%, which was attributed to its precipitation at high pH and adsorption on to iron hydroxides and activated carbon. Nickel purification was achieved by further coagulation as the equilibrium concentration of Ni was lower than 0.1 mg/L. Therefore, our work provides a promising approach for simultaneous recovery of P and removal of Ni from electroplating wastewater. [ABSTRACT FROM AUTHOR]

This study was designed to fully characterize Porphyra haitanensis polysaccharides, and to evaluate their antioxidant activity. The polysaccharides primarily contained galactose and 3,6-anhydrogalactose in a molar ratio of 1.2:1.0, respectively and sulfate content about 3.8%. The molecular weight of polysaccharides is 2.5 × 10 5 Da. Scanning electron microscopy and atomic force microscopy of the polysaccharides pointed towards an irregular network with more or less hexagonal and a few rectangular pores. The chemical structure was confirmed through Fourier transform infrared spectroscopy, and 1D and 2D nuclear magnetic resonance structural characterization wherein → 4-3,6-anhydro-α-L-galactopyranose-(1 → 3)-β-D-galactopyranose segments. The extracted polysaccharides revealed relatively high 2, 2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging activity (53.16% at 2 mg/mL), moderate 2,2-diphenyl-1-picrylhydrazyl radical scavenging efficacy (34.63% at 2 mg/mL), and low hydroxyl radical scavenging potential (23.80% at 2 mg/mL). Further purification of these polysaccharides, hence, is advised for their potential role as antioxidants in the food, pharmaceutical and cosmeceutical industry., Competing Interests: Declaration of Competing Interest None worth declaring., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Adverse health effects of ambient PM 2.5 ( d p < 2.5 μm) can be associated with the production of reactive oxygen species (ROS), among which hydroxyl radical (•OH) is the most reactive. However, •OH generated by PM 2.5 has not been quantified and studied in the North China Plain (NCP), which has suffered from heavy air pollution in recent years. In this study, PM 2.5 samples were collected at an urban site (Beijing) and a suburban site (Wangdu), extracted in a cell-free surrogate lung fluid (SLF), and •OH generated in the extracts were quantified. The results show that more •OH is produced on heavily polluted days than that on clean days (2.0 and 1.6 times higher in Beijing and Wangdu, respectively). The production of •OH per unit mass (ng/μg·PM 2.5 ) decreases with the increase of ambient PM 2.5 concentration because SO 4 2- , NO 3 - , and NH 4 + dominate the increased PM 2.5 , while these secondary inorganic components do not contribute to the generation of •OH. Trace metals (e.g., Fe, Cu, Se) and carbonaceous species (organic carbon and elemental carbon) correlate well with the •OH production, indicating that particles from combustion sources including coal combustion, vehicle exhaust, and industry contribute more to •OH generation.

Precursors that can be transformed into perfluoroalkyl acids (PFAAs) have not been investigated in detail. In this study, the levels of potential PFAA precursors in the Jiaozhou Bay, inflowing rivers, and STP (sewage treatment plant) effluents were investigated by converting all PFAA precursors into perfluorinated carboxylic acids (PFCAs) by chemical oxidation. The significance of controlling PFAA precursors was indicated by the ratios of PFCAs converted by the oxidative treatment of precursors to PFAAs before oxidation (∑△[PFCA C4-C12 ]/∑[PFAA] before oxidation ). The higher levels of △[PFCA C4-C12 ] (average = 18.89 ng/L) and lower ratios (∑△[PFCA C4-C12 ]/∑[PFAA] before oxidation , average = 0.21) were revealed in the STP effluents rather than in the water of the Jiaozhou Bay and rivers, which implied the precursors conversion during the sewage treatment process. The concentrations of △[PFCAs] and the aforementioned ratios showed apparent spatial and temporal differences. These results indicated that STPs were the important sources of precursors to other water bodies., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Acetylacetone (AcAc) is a common atmospheric oxygenated volatile organic compound due to broad industrial applications, but its atmospheric oxidation mechanism is not fully understood. We investigate the mechanism, kinetics, and atmospheric fate of the OH-initiated oxidation for the enolic and ketonic isomers of AcAc using quantum chemical and kinetic rate calculations. OH addition to enol-AcAc is more favorable than addition to keto-AcAc, with the total rate constant of 1.69 × 10 -13 exp(1935/T) cm 3 molecule -1 s -1 over the temperature range of 200-310 K. For the reaction of the enol-AcAc with OH, the activation energies of H-abstraction are at least 4 kcal mol -1 higher than those of OH-addition, and the rate constants for OH-addition are by 2-3 orders of magnitude higher than those for H-abstraction. Oxidation of AcAc is predicted to yield significant amounts of acetic acid and methylglyoxal, larger than those are currently recognized. A lifetime of less than a few hours for AcAc is estimated throughout the tropospheric conditions. In addition, we present field measurements in Beijing and Nanjing, China, showing significant concentrations of AcAc in the two urban locations. Our results reveal that the OH-initiated oxidation of AcAc contributes importantly to ozone and SOA formation under polluted environments.

A series of processes by biofilter and Fenton oxidation to treat mature landfill leachate has been devised. At a hydraulic loading rate of 20 l m(-3)d(-1), a biofilter packed with aged refuse is found to remove 80% of chemical oxygen demand (COD), 89% of ammonia nitrogen and 96% of total phosphorus (TP). Particularly, TP levels dropped below 1 mg l(-1). The optimal condition for Fenton oxidation was selected to be an initial pH of 5, a dosage of 0.01 and 0.02 mol l(-1) of FeSO(4) and H(2)O(2), respectively, and a duration of 3h, where COD removal efficiency reaches 58.6%, and BOD(5)/COD ratio is raised from 0.05 to 0.20. Subsequent treatment by a biofilter packed with slag reduces COD, ammonia nitrogen levels to less than 100, 25 mg l(-1), respectively. A pilot scale experiment conducted in situ demonstrates that this series of processes exhibits a high efficiency in removing pollutants from mature landfill leachate and it is viable for application., (Copyright © 2010 Elsevier Ltd. All rights reserved.)