Computational study on the mechanism and kinetics of NO3-initiated atmosphere oxidation of vinyl acetate

It is known the NO3 radical contributes to the oxidation of volatile organic compounds in the atmosphere in the night, leading to the formation of carbonyl compounds and organic nitrates. The mechanistic and kinetic properties of NO3-initiated oxidative degradation of vinyl acetate (VAC), a typical unsaturated ester, have been studied using density functional method. According to the computational results, two types of primary reactions were identified: NO3-addition and H-abstraction. The NO3-addition reaction especially the C-beta-addition pathway dominates the entrance channel of NO3 into VAC while the H-abstraction reaction is negligible. Further reactions of the two adducts were discussed in the presence of O-2/NOx. The rate constants were estimated by using the MultiWell software. The overall rate constant of NO3-initiated oxidation of VAC was about 7.30 x 10(-15) cm(3) molecule(-1) s(-1) at 298.15 K and atmospheric pressure, in good agreement with the experimental value of (7.30 +/- 1.8) x 10(-13) cm(3) molecule(-1) s(-1). The atmospheric lifetime of VAC reacting with NO3 radicals (5.0 x 10(8) molecule cm(-3)) is about 76.1 h under atmospheric conditions

OH-Initiated Tropospheric Photooxidation of Allyl Acetate (AAC): A Theoretical Study

The mechanisms of OH-initiated oxidation of allyl acetate (AAC) in the presence of O2/NO have been investigated by performing Density Functional Theory (DFT) calculations. Two patterns (OH-addition and H-abstraction) of the initial reaction and the subsequent reactions of the primarily produced intermediates (IM1, IM2 and IM4) have been proposed. The OH addition reactionsare more favorable than the H abstraction reactions, but H abstraction from the CH2group cannot be ignored. The major degradation products have been identified. The rate coefficients and the branching ratios of the primary reactions are obtained over the temperature of 200-500 K and the pressure range of 0.001-1000 atm. The total rate coefficient is 3.17 Ă 10-11 cm3 molecule-1 s-1 at 298 K and 1 atm. With respect to the typical concentration of OH radical (2.0 Ă 106 molecule cm-3), the atmospheric lifetime of AAC is estimated to be 4.40 hours.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Theoretical Investigation on Mechanistic and Kinetic Transformation of 2,2′,4,4′,5-Pentabromodiphenyl Ether

This study investigates the decomposition of 2,2′,4,4′,5-pentabrominated diphenyl ether (BDE99), a commonly detected pollutant in the environment. Debromination channels yielding tetrabrominated diphenyl ethers and hydrogen abstracting aromatic bromine atom formations play significant roles in the reaction of BDE99 + H, in which the former absolutely predominates bimolecular reactions. Polybrominated dibenzo-<i>p</i>-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs) can be produced during BDE99 pyrolysis, especially for PBDFs under inert conditions. The expected dominant pathways in a closed system are debromination products and PBDF formations. The bimolecular reaction with hydroxyl radical mainly leads to hydroxylated BDE99s rather than hydroxylated tetrabrominated diphenyl ethers. PBDDs are then generated from <i>ortho</i>-hydroxylated PBDEs. HO₂ radical reactions rarely proceed. The total rate constants for the BDE99 reaction with hydrogen atoms and hydroxyl radicals exhibit positive dependence on temperature with values of 1.86 × 10^–14 and 5.24 × 10^–14 cm³ molecule^–1 s^–1 at 298.15 K, respectively

Computational Study on the Mechanisms and Rate Constants of the Cl-Initiated Oxidation of Methyl Vinyl Ether in the Atmosphere

The Cl-initiated oxidation reactions of methyl vinyl ether (MVE) are analyzed by using the high-level composite method CBS-QB3. Detailed chemistry for the reactions of MVE with chlorine atoms is proposed according to the calculated thermodynamic data. The primary eight channels, including two Cl-addition reactions and six H-abstraction reactions, are discussed. In accordance with the further investigation of the two dominant additional routes, formyl chloride and formaldehyde are the major products. Over the temperature range of 200–400 K and the pressure range of 100–2000 Torr, the rate constants of primary reactions are calculated by employing the MESMER program. H-abstraction channels are negligible according to the value of rate constants. During the studied temperature range, the Arrhenius equation is obtained as <i>k</i>_tot = 5.64 × 10^–11 exp­(215.1/<i>T</i>). The total rate coefficient is <i>k</i>_tot = 1.25 × 10^–10 cm³ molecule^–1 s^–1 at 298 K and 760 Torr. Finally, the atmospheric lifetime of MVE with respect to Cl is estimated to be 2.23 h

Sandstorms in the Yellow River Basin, China in the 21st century: Spatiotemporal pattern and variation trend

Sandstorm, as a disastrous weather phenomenon, seriously threatens the ecological environment and human health. In this study, the normalized brightness temperature dust index (NBTDI) data set of sandstorms in Yellow River Basin, China during 2000–2021 was constructed. Based on this, the temporal and spatial distribution pattern of sandstorms in the Yellow River Basin in the 21st century was analyzed. The variation trend of NBTDI in the past 22 years was discussed. The results showed that the interannual variation of sandstorms in the 21st century weakened first and then intensified. From the perspective of seasonal variation, sandstorm events occurred most frequently in spring (92.4%), followed by winter (5.6%), and occasionally in summer and autumn. In space, the distribution of sandstorms in the Yellow River Basin had obvious spatial heterogeneity. The central location of the sandstorm in the Yellow River Basin moved slightly to the north, but all of them were concentrated on desert areas. This was caused by the combination of unique geographical location and meteorological factors. The natural climate was closely related to the occurrence of sandstorms. The variation trend of long time-series NBTDI indicated that there were long memories between 22 years of sandstorms. NBTDI had an increasing trend in the long time series. In the future, sandstorms will become more frequent, in line with past trends. This study provides important data support for comprehensive understanding of extreme sandstorm weather, and has important significance for large-scale and long-term monitoring of sandstorm weather

Bioaugmentation treatment of PV wafer manufacturing wastewater by microbial culture

The wastewater of silicon photovoltaic (PV) battery manufacturing contained polyethylene glycol (PEG) and detergents, which possessed the characteristics of high content of organics and low bioavailability, and then resulted in high treatment costs. To address the difficulties of existing treatment facilities in stably meeting discharge standards, eight tons of microbial culture (consisting of Bacillus sp. and Rhodococcus sp.) were added into the aerobic treatment unit. Subsequently, the effectiveness of the microbial culture in small-scale biological wastewater treatment was evaluated, and the operating conditions for engineering applications were optimized. The application study showed that the average chemical oxygen demand (COD) removal efficiency reached 95.0% when the pH value was 7, the gas-water ratio was 28: 1, the reflux ratio was 50%, which indicated an increase of 51.2% contrasting with the situation without bioaugmentation. The volume load of the treatment facilities after augmentation increased by 127.9% and could tolerate the COD shock load reached 2,340 mg.L-1. At last, the effluence met the class I standard of the Integrated Wastewater Discharge Standard (GB8978-1996)