Empirical Kinetic Model Research Articles

Effective sonophotocatalytic degradation of tetracycline in water: Optimization, kinetic modeling, and degradation pathways

Hybrid advanced oxidation processes (AOPs) are gaining interest in degradation of variety of recalcitrant compounds for water and wastewater treatment, due to possible synergistic effects. The present study systematically evaluated the degradation of tetracycline (TC) with a sonophotocatalytic process combining acoustic cavitation (sonocavitation) and photocatalysis based on N-doped TiO2 catalyst. The TC degradation rate constant was 2.4 × 10−2 min−1, i.e., much higher than individual sonocatalytic (0.5 × 10−2 min−1) and photocatalysis (0.6 × 10−2 min−1) processes at the optimized conditions. The synergy index was 2.14, which reveals a significant improvement in the process performance. Maximum TC degradations of 55.5 ± 1.8 % for photocatalysis, 66.4 ± 1.8 % for sonocatalysis, and 79.5 ± 0.3 % for sonophotocatalysis were observed for 10 mg L−1 initial TC concentration after 90 min of treatment. The photocatalytic experiments were extended further to 210 min to achieve a maximum degradation of 78.9 ± 0.2 % at the optimized condition. Scavenging experiments confirmed that hydroxyl radicals (•OH), electron holes (h+), and superoxide radical anions (O2−•) played a significant role in the degradation of TC. Further, the degradation intermediates for each process were identified and degradation pathways were proposed. Empirical kinetic models based on operational parameters were also developed and validated.

Mathematical modeling of the enzymatic hydrolysis of lignocellulosic waste in membrane bioreactor considering transport phenomena

Enzymatic hydrolysis is a crucial step in processing lignocellulosic biomass into biofuels and other valuable products in biorefineries. Applying a membrane reactor to realize this process allows for continuous separation of inhibitory end-products, thus improving process efficiency. Developed so far models have generally been dedicated to describing the reaction kinetics without considering transport phenomena and flux decline prediction. In the present paper, a new mathematical model simulating the hydrolysis process course in membrane bioreactor was established. Compared to previous reports, our study presents a novel approach to modeling the process accounting for the reaction course and permeate flux decline depending on reaction hydrodynamics. A surface renewal theory and empirical reaction kinetic model were implemented to simulate the influences of the operating parameters on the permeate flux and the monosaccharide concentration in the permeate. A procedure to determine the model parameters with experimental data was also presented. The proposed model simulated experimental data with good accuracy (R2>0.97). The total mass of glucose and xylose produced during 10 h of the hydrolysis performed under mixing conditions equaled 2.37 g and 2.39 g for the pressure of 0.4 and 0.6 bar, respectively. They correspond to the high hydrolysis yield, equaled in average to 99.1 %.

Analysis of Photochemical Characteristics and Sensitivity of Atmospheric Ozone in Nanjing in Summer

Tropospheric ozone (O3) is mainly produced through a series of photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). The reaction process presents complex non-linear relationships. In this work, datasets of atmospheric ozone and volatile organic compounds (VOCs) observed during the summer of 2018 in Nanjing were used. Combining with the framework for 0-D atmospheric model-master chemical mechanism (F0AM-MCM), the characteristics of photochemical reactions for ozone (O3) formation in Nanjing during the O3 episode days and non-episode days were investigated. The results showed that φ(O3) and φ(TVOCs) in the O3 episode days were 47.8×10-9 and 49.0×10-9, respectively, exceeding those in the non-episode days by factors of 1.8 and 1.6. Furthermore, F0AM, the empirical kinetic modeling approach (EKMA), and relative incremental reactivity (RIR) were utilized for the calculation of ozone chemical sensitivity. It was found that O3 formation in Nanjing was attributed to both VOCs and NOx limitation. In addition, the modeled ·OH and HO2 concentrations in the O3 episode days were 1.3 and 1.8 times higher than those in the non-episode days. The higher formation and loss rates of ·OH and HO2 were also found during O3 episode days. These findings reflected that the enhancements of atmospheric oxidation capacity resulted in increased production rates of O3, providing an explanation for the enhancements of O3 concentrations in Nanjing during the O3 episode days. The findings also improved the understanding of the O3 photochemical characteristics over Nanjing in the summer during the O3 episode days.

Quantitative Characterization of the Volatility Distribution of Organic Aerosols in a Polluted Urban Area: Intercomparison Between Thermodenuder and Molecular Measurements

AbstractTo quantify the volatility of organic aerosols (OA), a comprehensive campaign was conducted in the Chinese megacity. Volatility distributions of OA and particle‐phase organic nitrate (pON) were estimated based on five methods: (a) empirical method and (b) kinetic model based on the measurement of a thermodenuder (TD) coupled with an aerosol mass spectrometer; (c) Formula‐based SIMPOL model‐driven method; (d) Element‐based estimations using molecular formula measurements of OA; and (e) gas/particle partitioning. Our results demonstrate that the ambient OA volatility distribution shows good agreement between the two heating methods and the formula‐based method when assuming ambient OA was mainly composed of organic nitrate (pON), organic sulfate and acid groups using the SIMPOL model. However, the element‐based method tends to overestimate the volatility of OA compared to the above three methods, suggesting large uncertainties in the parameterizations or in the representativeness of the molecular measurements that need further refinement. The volatility of ambient OA is generally lower than that of the laboratory‐derived secondary OA, emphasizing the impact of aging. A large fraction at the higher and lower volatility ranges (approximately log C* ≤ −9 and ≥2 μg m−3) was found for pON, implying the importance of both extremely low volatile and semi‐volatile species. Overall, this study evaluates different methods for volatility estimation and gives new insight into the volatility of OA and pON in urban areas.

Characteristics and Sensitivity Analysis of Ozone Pollution in a Typical Inland City in China

In this research, long-term monitoring data from 2020 to 2023 were used to characterize O3 pollution in a typical inland city in northwest China (34°21′ N 109°30′ E), which indicated that ozone pollution yielded typical regular fluctuations and high ozone concentrations from April to September were observed. Ozone varied in the range of 16–176 μg/m3, and maximum peaks were found usually at 14:00–17:00 in June and July. Correlation analysis showed a significant positive relationship between ozone and temperature, with correlation coefficients of 0.93. The wind speed exhibits a similar variation as ozone. Meanwhile, negative correlations were not so notably observed among ozone, humidity, VOCs, and NOx. Finally, the empirical kinetic model OZIPR (Ozone Isopleth Plotting Program for Research) was employed to analyze the sensitivity relationship among ozone and precursor compounds by calculating EMKA (Empirical Kinetics Modeling Approach) curves. The EKMA analysis results showed that during the whole ozone pollution period, ozone formation is mainly dominated by VOCs due to all the ratios of VOCs/NOx which fell in the VOCs control region. Therefore, VOCs should be priority controlled and more measures should be taken for better ozone pollution control abatement.

NAGPKin: Nucleation-and-growth parameters from the kinetics of protein phase separation.

The assembly of biomolecular condensate in eukaryotic cells and the accumulation of amyloid deposits in neurons are processes involving the nucleation and growth (NAG) of new protein phases. To therapeutically target protein phase separation, drug candidates are tested in in vitro assays that monitor the increase in the mass or size of the new phase. Limited mechanistic insight is, however, provided if empirical or untestable kinetic models are fitted to these progress curves. Here we present the web server NAGPKin that quantifies NAG rates using mass-based or size-based progress curves as the input data. A report is generated containing the fitted NAG parameters and elucidating the phase separation mechanisms at play. The NAG parameters can be used to predict particle size distributions of, for example, protein droplets formed by liquid-liquid phase separation (LLPS) or amyloid fibrils formed by protein aggregation. Because minimal intervention is required from the user, NAGPKin is a good platform for standardized reporting of LLPS and protein self-assembly data. NAGPKin is useful for drug discovery as well as for fundamental studies on protein phase separation. NAGPKin is freely available (no login required) at https://nagpkin.i3s.up.pt.

Characterization, source apportionment, and risk assessment of ambient volatile organic compounds in urban and background regions of Hainan Island, China

The pollution characteristics of volatile organic compounds (VOCs) in urban and background regions in Hainan province, China, were determined based on field measurements of CO, NO, NO2, O3, VOCs, and meteorological parameters conducted at Haikou (HK, an urban site) and Wuzhishan (WZS, a background site) in 2019. The annual average concentration of VOCs at HK was 13.1 ppb, which was 2.2 times higher than that at WZS (6.0 ppb). VOC concentrations at HK were higher in winter, whereas there was no significant monthly variation at WZS. Diurnal variations in VOCs were characterized by two peaks at HK, attributable to emissions during morning and evening rush-hour traffic. At WZS, the diurnal variations of VOCs were characterized by one peak at 13:00–16:00, corresponding to the high temperature and intense sunlight in the afternoon. The total O3 formation potential of ambient VOCs was 135.1 g g−1 at HK and 80.6 g g−1 at WZS, with the O3 formation potential of alkenes accounting for 53.4% and 47.2%, respectively. The potential source region of VOCs at both sites was likely the southeastern ocean region of China (i.e., Guangdong, Guangxi, Hunan, and Jiangxi provinces) and Vietnam, Cambodia, and Thailand. Using on an empirical kinetic modeling approach, O3 formation at HK occurred under a mixed-limited region, and at WZS under a NOx-limited region. Traffic emissions were the largest contributor to VOCs at HK, accounting for 38.7%, followed by solvents (19.6%), combustion (15.2%), industrial sources (15.0%), and plant sources (11.5%). At WZS, traffic accounted for 39.6% of VOCs, similar to HK, whereas the contribution of industrial sources (22.1%) was higher. Although there are few vehicles and little industry around WZS, the long-distance transport of VOCs emitted elsewhere by these sources had a significant influence on the region's VOCs. The contribution of plant sources of VOCs was 1.5 times higher at WZS (17.0%) than at HK. None of the VOC species posed significant non-carcinogenic or carcinogenic risks at either HK or WZS.

TEMPERATURE-DEPENDENT KINETICS OF ANTHOCYANINS EXTRACTION FROM RED ROSE PETALS

The red rose is one of the perspective natural resources of anthocyanins, however kinetic study for anthocyanins extraction of red rose petals is not yet elucidated. Red rose petals were dried at 303 K and ground (particle size ~ 5 mm). The petals were extracted by aqueous acid solutions using conventional solid-liquid extraction. The efficiency of 0.1 M aqueous solutions of acids as extractants towards red rose anthocyanins was studied and it can be arranged in the following row: citric acid < acetic acid < hydrochloric acid. Kinetic investigations focusing on the temperature effect on solid-liquid extraction of anthocyanins from petals of red rose were performed at three temperatures (293, 313, and 333 K). Kinetic curves were obtained using an aqueous solution of hydrochloric acid. It was found that the rate of extraction of anthocyanins was very fast at the beginning, but it began to slow down after 60 minutes for all temperatures. The experimental kinetic curves of the extraction of anthocyanins at different temperatures were obtained and analyzed using common empirical kinetic models (the first-order, second-order kinetic models, the Peleg model, and the power-law model). The second-order kinetic model provided the best agreement with the experimental results in terms of statistical parameters (coefficient of determination (R2) and average relative error (ARE)) than other studied models. As temperature increases, the second-order rate constant values and the initial extraction rate values also increased. The second-order rate constants were used to evaluate the activation energy of extraction. The calculated activation energy of the anthocyanin extraction is 39.3 kJ/mol, which is an indication of an endothermic process. Obtained data can be used to predict the extraction of anthocyanins from red rose petals.

Experimental Design of Oxidative Desulfurization of Kerosene Through Response Surface Methodology (RSM)

Sulfur compound content in fuels is one of the most undesirable pollutions regarding standard environmental regulations that demand to reduce sulfur concentration limit to 5-10% in fuels. Hence, kerosene’s oxidative desulfurization (ODS) as a model fuel (sulfur content 1158ppm) with air as an oxidant is studied. The goal of the study is to use two different synthesized nanosilica-supported catalysts, CuO/SiO2 (CAT-1) and CuO/TiO2-SiO2 (CAT-2), for the ODS of kerosene. Thirty-two experimental runs were designed via Central Composite Design (CCD) to select the experiments that will be utilized most efficiently. The analysis of variance (ANOVA) was used for statistical analysis to determine the models’ significance. The Response surface methodology (RSM) was used to determine the optimum conditions and parameters significantly affecting the response. Temperature and time are two variables studied due to their impact on oxidative desulfurization. The actual results of sulfur conversion in kerosene from lab experiments were 87% with a sulfur content of 153.3ppm and 99.22% with a sulfur content of 8.9ppm by CAT-1 and CAT-2, respectively, at conditions of 140°C and 100min. The predicted results from experimental design were 86.66% and 99.8% by CAT-1 and CAT-2 at conditions of 140°C and 100min, showing errors less than 3.1% and 1.2% for CAT-1 and CAT-2, respectively, from ANOVA. The optimal parameters of ODS were determined through the sulfur conversion maximization by numerical optimization via ANOVA. The results showed that the maximum conversion by CAT-1 was 99.5% at 140 min and 180°C, and by CAT-2 was 99.7% at 100.1 min and 140.1°C. Also, the rate data were fitted with an empirical kinetic model. The results showed that CAT-1 and CAT-2 activation energies were Ea= 28.2 kJ/mol and Ea= 38.7 kJ/mol, respectively.

Ambient Volatile Organic Compound Characterization, Source Apportionment, and Risk Assessment in Three Megacities of China in 2019.

In order to illustrate pollution characterization, source apportionment, and risk assessment of VOCs in Beijing, Baoding, and Shanghai, field observations of CO, NO, NO2, O3, and volatile organic compounds (VOCs) were conducted in 2019. Concentrations of VOCs were the highest in Beijing (105.4 ± 52.1 ppb), followed by Baoding (97.1 ± 47.5 ppb) and Shanghai (91.1 ± 41.3 ppb). Concentrations of VOCs were the highest in winter (120.3 ± 61.5 ppb) among the three seasons tested, followed by summer (98.1 + 50.8 ppb) and autumn (75.5 + 33.4 ppb). Alkenes were the most reactive VOC species in all cities, accounting for 56.0%, 53.7%, and 39.4% of ozone formation potential in Beijing, Baoding, and Shanghai, respectively. Alkenes and aromatics were the reactive species, particularly ethene, propene, 1,3,5-trimethylbenzene, and m/p-xylene. Vehicular exhaust was the principal source in all three cities, accounting for 27.0%, 30.4%, and 23.3% of VOCs in Beijing, Baoding, and Shanghai, respectively. Industrial manufacturing was the second largest source in Baoding (23.6%) and Shanghai (21.3%), and solvent utilization was the second largest source in Beijing (25.1%). The empirical kinetic modeling approach showed that O3 formation was limited by both VOCs and nitric oxides at Fangshan (the suburban site) and by VOCs at Xuhui (the urban site). Acrolein was the only substance with an average hazard quotient greater than 1, indicating significant non-carcinogenic risk. In Beijing, 1,2-dibromoethane had an R-value of 1.1 × 10-4 and posed a definite carcinogenic risk.

Abundant nitrogen oxide and weakly acidic environment synergistically promote daytime particulate nitrate pollution

Nitrate is formed through the chemical production of gas-phase nitric acid and subsequent partitioning to the aerosol phase during the daytime. Many studies in the past separated these two aspects, even though they occur simultaneously in the atmosphere. To better understand the nitrate formation mechanism and effectively mitigate its production, it is necessary to consider the synergy between these two mechanisms. For this, we analyze hourly-speciated ambient observations data, with EK&TMA (Empirical Kinetic & Thermodynamic Modeling Approach) map to comprehensively explore the factors controlling nitrate production. Results show that precursor NO2 concentration and aerosol pH, which are related to anthropogenic activities, are the two major factors for chemical kinetics production and gas/particle thermodynamic partitioning processes respectively. Abundant NO2 and weakly acidic environments are favorable conditions for daytime particulate nitrate pollution, thus collaborative control of coal source, vehicle source, and dust source is needed to alleviate nitrate pollution.

Characteristics and source apportionment of ambient volatile organic compounds and ozone generation sensitivity in urban Jiaozuo, China

In recent years, many cities have taken measures to reduce volatile organic compounds (VOCs), an important precursor of ozone (O3), to alleviate O3 pollution in China. 116 VOC species were measured by online and offline methods in the urban area of Jiaozuo from May to October in 2021 to analyze the compositional characteristics. VOC sources were analyzed by a positive matrix factorization (PMF) model, and the sensitivity of ozone generation was determined by ozone isopleth plotting research (OZIPR) simulation. The results showed that the average volume concentration of total VOCs was 30.54 ppbv and showed a bimodal feature due to the rush-hour traffic in the morning and at nightfall. The most dominant VOC groups were oxygenated VOCs (OVOCs, 29.3%) and alkanes (26.7%), and the most abundant VOC species were acetone and acetylene. However, based on the maximum incremental reactivity (MIR) method, the major VOC groups in terms of ozone formation potential (OFP) contribution were OVOCs (68.09 µg/m3, 31.5%), aromatics (62.90 µg/m3, 29.1%) and alkene/alkynes (54.90 µg/m3, 25.4%). This indicates that the control of OVOCs, aromatics and alkene/alkynes should take priority. Five sources of VOCs were quantified by PMF, including fixed sources of fossil fuel combustion (27.8%), industrial processes (25.9%), vehicle exhaust (19.7%), natural and secondary formation (13.9%) and solvent usage (12.7%). The empirical kinetic modeling approach (EKMA) curve obtained by OZIPR on O3 exceedance days indicated that the O3 sensitivity varied in different months. The results provide theoretical support for O3 pollution prevention and control in Jiaozuo.

Developing and modelling of sustainable protein extraction using ammonium hydroxide – A recoverable and reusable solvent

Plant protein demand is growing as more people adopt a healthier and sustainable lifestyle. Since plant proteins are cell wall protected, extraction process that breaks cell-wall barrier is needed to obtain protein. However, the conventional extraction methods use non-reusable and non-recoverable solvents. Therefore, the goal of this research is to develop and model sustainable protein extraction using NH4OH—a recoverable and reusable solvent. Soybean protein was extracted at a temperature of 55 °C, varying particle sizes (>1, 0.425 – 1, 0.25–0.425, and<0.25 mm), times (0, 3, 6, 12, and 48 h), NH4OH concentrations (1%, 2.5%, 5%, 10% and 15%) and solid loading (1:10) using a full factorial experimental design. The empirical kinetic models for soybean protein extraction were analyzed with parabolic diffusion model, So & MacDonald’s model, hyperbolic, and first order model. The highest protein yield of 59% was obtained at 0.425 – 1 mm particle size, 12 h, and 1% NH4OH. Amine concentrations of extracted proteins were poorly correlated with protein yield evincing that extraction conditions to obtain the high yield did not cause protein hydrolysis. Three out of the four models gave a good fit. The best fit was So & MacDonald’s model, with a minimum root mean square error (RMSE) of 0.14 and maximum coefficient of linear correlation (R) of 0.89. In conclusion, NH4OH is a viable and sustainable solvent to extract plant protein and can be utilized for industrial plant protein production.

Optimization and kinetic studies of d-galacturonic acid extraction from basil seed using different extraction techniques

This study presents d-galacturonic acid extraction from basil seeds using stirred reactor extraction, conventional soxhlet extraction, and ultrasonic extraction techniques. Different process parameters such as type of solvent, pH (2–9.5), solid-to-solvent ratio (0.5:100–2:100), time(10–70 min), temperature (40–90 °C), and agitation speed (100-700RPM) were optimized. The yield of D-gala using ultrasound-assisted extraction (104.25 mg/g of basil seeds) was higher as compared to the stirred reactor (92.64 mg/g of basil seeds) and soxhlet extraction (52.2 mg/g of basil seeds). Moreover, the time required for extraction using ultrasound was significantly less (15 min) as compared to the stirred reactor (60 min) and soxhlet extraction (280 min). The process effectiveness in terms of yield of D-gala per unit energy dissipated in ultrasound-assisted extraction (12.46 mg/g of basil seed kJ) was around 13 times greater than stirred reactor (0.975 mg/g of basil seed kJ) and about 63 times greater than soxhlet extraction (0.201 mg/g of basil seed kJ). As a result, ultrasonic extraction is regarded as the best alternative approach to the stirred reactor and soxhlet extraction for getting a higher d-galacturonic acid yield from basil seeds. An empirical kinetic model of second order rate equation and a mathematical model using a nonlinear regression technique was investigated for the process, which shows numerical correlation and significance factor between the yield and all other parameters. The detailed characterization of the extracted components has been carried out using Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), and Liquid chromatography and mass spectroscopy (LCMS).

Ozone Formation at a Suburban Site in the Pearl River Delta Region, China: Role of Biogenic Volatile Organic Compounds

Ozone (O3) is becoming an increasingly concerning air quality problem in China, and previous O3 control strategies focused primarily on reducing anthropogenic volatile organic compounds (AVOCs), while neglecting the role of biogenic VOCs (BVOCs) in O3 formation. In this study, a field campaign was conducted at a suburban site in the Pearl River Delta region of China with high BVOC emissions from 29 August to 3 September 2020. An empirical kinetic modelling approach (EKMA) showed that VOC-limited was the dominant feature for O3 formation at the site. The relative incremental reactivity (RIR) values calculated by the box model (AtChem2-MCM) revealed that isoprene, formaldehyde, methylglyoxal and acetaldehyde had the highest RIRs. Simulation results from the box model also showed that isoprene played a substantial role in the formation of secondary carbonyls, especially contributing 32–92% to the formaldehyde production rate. Box model simulations further showed that during the O3 pollution period with high BVOC emissions, only near zero AVOC emissions could prevent O3 if the levels of nitrogen oxides (NOx) remained unchanged. The results suggest that the presence of high BVOC emissions can greatly impact efforts to control O3 by reducing AVOCs, particularly in regions with relatively high NOx levels (up to 51 ppbv in this study). In the long term, it may be essential to control NOx and choose low BVOC-emitting tree species in urban planning to address this issue, particularly as BVOC emissions are projected to become a more significant source of reactive VOCs with enhanced control of AVOCs.

Elucidate the formation mechanism of particulate nitrate based on direct radical observations in the Yangtze River Delta summer 2019

Abstract. Particulate nitrate (NO3-) is one of the dominant components of fine particles in China, especially during pollution episodes, and has a significant impact on human health, air quality, and climate. Here a comprehensive field campaign that focuses on the atmospheric oxidation capacity and aerosol formation and their effects in the Yangtze River Delta (YRD) was conducted from May to June 2019 at a regional site in Changzhou, Jiangsu Province in China. The concentrations of NO3-, OH radicals, N2O5, NO2, O3, and relevant parameters were measured simultaneously. We showed a high NO3- mass concentration with 10.6 ± 8.9 µg m−3 on average, which accounted for 38.3 % of total water-soluble particulate components and 32.0 % of total PM2.5, followed by the proportion of sulfate, ammonium, and chloride by 26.0 %, 18.0 %, and 2.0 %, respectively. This result confirmed that the heavy nitrate pollution in eastern China happened not only in winter, but also in summer. This study's high nitrate oxidation ratio (NOR) emphasized the solid atmospheric oxidation and fast nitrate formation capacity in the YRD. It was found that OH + NO2 during daytime dominated nitrate formation on clean days, while N2O5 hydrolysis vastly enhanced and became comparable with that of OH + NO2 during polluted days (67.2 % and 30.2 %, respectively). The updated observed-constraint Empirical Kinetic Modeling Approach (EKMA) was used to assess the kinetic controlling factors of both local O3 and NO3- productions, which indicated that the O3-targeted scheme (VOCs : NOx = 2:1) is adequate for mitigating the O3 and nitrate pollution coordinately during summertime in this region. Our results promote the understanding of nitrate pollution mechanisms and mitigation based on field observation and model simulation and call for more attention to nitrate pollution in the summertime.

Indirect oxidation mechanism governing in P-rGO/Ti anode with C2-PO2/rGO configuration for efficient 2-Methyl-4-Isothiazolin-3-one electrooxidation

A stable phosphorus-doped reduced graphene (P-rGO/Ti) anode applied in electrochemical oxidation was prepared for the degradation of 2-Methyl-4-Isothiazolin-3-one (MIT), a broad-spectrum biocide with high concentration and toxicity widely exists in reverse osmosis concentrates. The P-rGO/Ti anode had high oxygen evolution potential (2.434 V), which inhibited side reactions and accelerated the mineralization of MIT. The •OH quenching tests verified that the indirect oxidation on MIT degradation was up to 84.17 %, and the mechanism of indirect oxidation was proposed about the C2-PO2/rGO configuration of P-rGO was more conducive to adsorb H2O and supply electron, resulting in the elongated OH bond and then easily cleaved to produce more •OH via density functional theory calculations. Furthermore, an empirical kinetic model was established to predict MIT removal trend. The P-rGO/Ti electrode maintained favorable MIT removal efficiency and structural stability with a long-term operation experiment in 1200 min. Moreover, the degradation pathways of MIT were proposed based on UPLC-Q-TOF-MS analysis. This study profoundly reveals the indirect oxidation mechanism of different P-rGO configurations on inducing the generation of •OH, and provides a new perspective for the design of stable and efficient carbon materials in electrochemical oxidation for wastewater purification.

Variations, sources, and effects on ozone formation of VOCs during ozone episodes in 13 cities in China

In recent years, ozone (O3) pollution has worsened in China and contributes frequently to air pollution problems. To support the implementation of coordinated control for ozone and fine particulate matter, it is essential to study the chemical compositions and sources of volatile organic compounds (VOCs), which are the crucial precursor of both ozone and fine particulate matter. In this study, 117 volatile organic compounds were monitored in 13 cities in Beijing-Tianjin-Hebei Urban Agglomeration and Fenwei plain. Concentrations of total volatile organic compounds ranged from 42 to 279 μg/m3 during the monitoring episode. In all 13 cities, alkanes, halogenated hydrocarbons, aromatics and oxygenated volatile organic compounds (OVOCs) were the dominant volatile organic compounds. Contributions of alkanes, halogenated hydrocarbons, aromatics and oxygenated volatile organic compounds to total ozone formation potential (OFP) were 21.7%–32.6%, 21.0%–27.9%, 24.3%–50.8% and 28.6%–52.3%, respectively. Furthermore, the results of source apportionment by positive matrix factorization (PMF) model indicated that solvent usage, gasoline evaporation, vehicle emissions, petrochemical industry and combustion were essential volatile organic compounds sources in 13 cities. Moreover, the sensitivity of ozone production was studied using an Empirical Kinetic Modeling Approach (EKMA) model, and it was found that ozone formation was volatile organic compounds limited in all 13 cities.

Volatile Organic Compounds in the North China Plain: Characteristics, Sources, and Effects on Ozone Formation

Enhanced volatile organic compounds (VOCs) observations were made on ozone-exceeding days in June 2020 in Linyi, China. A total of 69 VOCs were collected (1 alkyne, 29 alkanes, 10 alkenes, 14 aromatic hydrocarbons, and 15 oxygenated volatile organic compounds (OVOCs)). The average concentration of total VOCs (TVOCs) was 36.0 ± 0.66 ppb, and the top three VOCs components were alkanes, OVOCs, and aromatic hydrocarbons, which accounted for 40.75%, 27.02%, and 11.30%, respectively. Based on the positive matrix factorization (PMF) model, the main sources of VOCs in Linyi City were divided into vehicle exhaust sources (39.11%), biomass combustion sources (21.82%), oil and gas volatilization sources (21.46%), and solvent use sources (17.61%). The ozone formation potential (OFP) contribution rate was dominated by alkenes, OVOCs, and aromatics, with contribution rates of 26.37%, 25.30%, and 23.65%, respectively. The top six VOCs that contributed the most to the OFP were formaldehyde, acetaldehyde, 1-butene, butadiene, trans-2-butene, and propylene. The empirical kinetic modelling approach (EKMA) curve indicated that the in situ ozone (O3) production was limited by VOCs, and reducing the concentration of O3 precursors in accordance with the VOCs/NOx concentration ratio of 1.15 can control O3 pollution more effectively.

New insight into formation mechanism, source and control strategy of severe O3 pollution: The case from photochemical simulation in the Wuhan Metropolitan Area, Central China

The Wuhan Metropolitan Area, located in Central China, has experienced severe O3 pollution in recent years; thus urging to diagnose formation regime and propose reasonable control strategies. Multi-source data of air pollutants and meteorological factors in 4 cities during August 2019 when severe regional O3 pollution occurred were obtained; then, in-situ O3 formation mechanism, the O3-precursors sensitivity, the sources and control strategies of O3 were evaluated based on the combination of the 0-D photochemical observation-based model and the positive matrix factorization model through the analysis of local ozone budget, the relative incremental reactivity, an empirical kinetic model approach and source apportionment. The results indicated the P(O3) (net O3 production rate) was 25 ppbv h−1 in Ezhou and 11–13 ppbv h−1 in other 3 cities. The dominated photochemical production of O3 was NO + HO2 reaction (62–71%), whereas the main pathway to destroy O3 during daytime was NO2 + OH (>70%) and nocturnal loss of O3 with alkenes even reached up to 39–46%. Generally, O3 formation was sensitive to AVOC (Anthropogenic Volatile Organic Compounds), in which reactive aromatics, OVOCs (Oxygenated VOCs), and alkenes (xylenes, ethylene, isoprene, methyl vinyl ketone, hexanal, toluene and methacrolein, specifically) as well as abundant i-pentane should be targeted to alleviate O3 pollution. The highly reactive VOCs sources for O3 formation in this region were vehicular exhaust (28–41%), industrial emissions (20–29% except Ezhou), and solvent use (17–29% except Huangshi). Co-reduction of O3 precursors in aforementioned reactive emissions according to optimal ratios of AVOC to NO2, i.e., 5:1 (Wuhan and Huanggang), 4:1 (Ezhou), and 6:1 (Huangshi), could achieve local O3 effective mitigation. Surprisingly, P(O3) could reduce by 38% and 48% under 40% AVOC cut accompanied by NO2 in more contaminated cities (Wuhan and Ezhou). Overall, our study provides new insight to future collaborative O3 alleviation strategies formulation in Central China, which quantified O3 formation at different precursors levels in different cities suffering from regional O3 pollution, concluded best precursors control ratios and confirmed validity of O3 mitigation through precursors-oriented emission reduction in vital sources.