Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the ...complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA), and benzoyl peroxide (BZP)) with dissolved SO2. Results show that due to the presence of the hydroperoxyl group in their structures, MHP and PAA are susceptible to forming inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability of PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within the pH 1–10 and 240–340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH3 and -C6H5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions.
The carbonyl fluoride (CF2O) is one of the significant atmospheric molecules, and its hydrolysis reaction has been considered the most potential removal process in the earth's troposphere. In this ...article, the hydrolysis reaction of CF2O assisted by H2O, basic (NH3 and CH3NHCH3), and acidic (H2SO4, HCOOH, and CF3COOH) catalysts have theoretically investigated using quantum chemical methods. These catalysts significantly decrease the hydrolysis reaction of barrier height by 20.4–28.8 kcal mol−1. Here two H‐transfer mechanisms have been identified in these catalyzed hydrolytic reactions as asynchronous collaborative caused by base molecules and the synchronous collaborative led by H2O and acid molecules. In addition, the rate coefficient and relative rate of all catalytic reactions have calculated using conventional transition state theory (TST) over a temperature range of 280–320 K. The results show that H2SO4 has the best catalytic effect without considering the concentration of catalyst molecules in the atmosphere. On the contrary, a high concentration of HCOOH (10 ppbv) is dominant in the catalytic reaction when considered the concentrations of catalyst molecules. In this work, it was identified that the catalytic efficiencies of H2O, acid and base molecules upon addition reaction between CF2O and H2O is not only related to their catalytic mechanisms but also depending upon their concentrations in the atmosphere.
This is the first detailed theoretical work on the kinetics and mechanism of the gas‐phase hydrolysis reaction of CF2O assisted by base and acid molecules. The mechanisms of the catalytic reaction of the two most important synchronous and asynchronous collaborative have also been explored and reported for the first time. The present results will provide a specific example of how the hydrolysis of CF2O assisted by H2O, base and acid occurs by two different mechanisms.
Quantum chemical calculations at B3LYP and CCSD(T) levels have been performed to investigate the effects of X (X = H2O, (H2O)2, NH3, and H3N···H2O) on HNO3 formation by the direct (HO2 + NO → HNO3) ...and indirect (N2O4 + H2O → HONO + HNO3) reaction of HO2 + NO. The results show that, for the direct H2O‐assisted reaction, the entrance of H2O···HO2 and NO is more important than the three other channels of HO2···H2O + NO, H2O···NO + HO2, and NO···H2O + HO2. In the H2O···HO2 + NO reactions, (H2O)2, NH3, and H3N···H2O have also been taken into account and substituted in place of H2O; however, their contributions are negligible compared with the H2O···HO2 + NO reaction. It is noted that the atmospheric gas‐phase reaction of H2O···HO2 + NO is not only competitive with the HO2 + NO2 → HNO3 reaction but can also compete well with the NO2 + HO reaction during the day and night at 298 K. Unlike the direct reaction assisted by X, the catalytic effect taken from X can be neglected in the indirect reaction of N2O4 + H2O → HONO + HNO3. However, theoretical results of the direct and indirect reaction of HO2 + NO above may be the main reason why the yield of HNO3 formation in HO2 + NO reaction increases experimentally in the presence of water.
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The effect of H2O, (H2O)2, NH3, and H3N···H2O on the HO2 + NO → HNO3 reaction was explored.
The effect of H2O is more obvious than the three other molecules of (H2O)2, NH3, and H3N···H2O.
At 298 K, the H2O···HO2 + NO reaction can not only compete with the naked HO + NO2 reaction but can also compete well with the NO2 + HO reaction during both the day and the night.
A detailed theoretical study on the reaction mechanisms for the formations of H2O2 + 3O2 from the self‐reaction of HO2 radicals under the effect of NH3, H3N···H2O, and H2SO4 catalysts was performed ...using the CCSD(T)/CBS//M06‐2X/aug‐cc‐pVTZ method. The rate constant was computed using canonical variational transition state theory (CVT) with small curvature tunneling (SCT). Our results indicate that NH3‐, H3N···H2O‐, and H2SO4‐catalyzed reactions could proceed through both one‐step and stepwise routes. Calculated rate constants show that the catalyzed routes in the presence of the three catalysts all prefer stepwise pathways. Compared to the catalytic efficiency of H2O, the efficiencies of NH3, H3N···H2O, and H2SO4 are much lower due to their smaller relative concentrations. The present results have provided a definitive example of how basic and acidic catalysts influence the atmospheric reaction of HO2 + HO2 → H2O2 + 3O2. These results further encourage one to consider the effects of basic and acidic catalysts on the related atmospheric reactions. Thus, the present investigation should have broad implications in the gas‐phase reactions of the atmosphere.
The HO2 + HO2 → H2O2 + 3O2 reaction assisted by NH3, H3N···H2O and H2SO4 was explored. In the presence of NH3, H3N···H2O and H2SO4, stepwise route is more favored energetically and kinetically than that of one‐step processes. Owing to the smaller concentrations of NH3 and H2SO4 than H2O in the atmosphere, the relative efficiency of NH3 and H2SO4 is much lower than that of H2O.
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.
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•First theoretical studies on the kinetics and mechanism of CF3CH2OCH2CF3 + Cl reaction.•Ab initio CCSD(T) and variational TST (CVT) are used for kinetic modeling.•Atmospheric ...degradation of CF3CH2OCH2CF3 was studied.•Calculated rate coefficients are in good agreement with the experimental values.•The estimated atmospheric lifetime of CF3CH2OCH2CF3 is 0.14 year.
The kinetics and mechanism of H–abstraction reaction between CF3CH2OCH2CF3 and Cl atoms are studied in the temperature range of 250–1000 K using CCSD(T)//BHandHLY/6-311++G(d, p) method and canonical variational transition state theory (CVT). Two potential pathways are observed for H–abstraction reaction and one of them is the predominant channel over the whole temperature range. IRC calculation reveals an indirect reaction process through the formation of pre- and post-reaction complexes. The calculated rate coefficient kCl = 6.95 × 10−13 cm3 molecule−1 s−1 is in good agreement with the experimental results. Reaction with Cl atoms may constitute a significant sink in the marine boundary layer.
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•Theoretical studies were performed on the kinetics and mechanism of the reaction of CF3CF2OCH3 with OH radicals.•First theoretical studies were carried out on the kinetics and ...mechanism of the reaction of CF3CF2OCHO with OH radicals.•Atmospheric degradation of CF3CF2OCH3 to CF3CF2OCHO was studied.•Calculated rate coefficients are in good agreement with the experimental values.•The estimated global warming potential of CF3CF2OCH3 is GWP100=497.
Theoretical studies have been performed on the kinetics, mechanism and thermochemistry of the hydrogen abstraction reactions of CF3CF2OCH3 (HFE-245mc) and CF3CF2OCHO with OH radical using DFT based M06-2X method. IRC calculation shows that both hydrogen abstraction reactions proceed via weakly bound hydrogen-bonded complex preceding to the formation of transition state. The rate coefficients calculated by canonical transition state theory along with Eckart’s tunnelling correction at 298K: k1(CF3CF2OCH3+OH)=1.09×10−14 and k2(CF3CF2OCHO+OH)=1.03×10−14cm3molecule−1s−1 are in very good agreement with the experimental values. The atmospheric implications of CF3CF2OCH3 and CF3CF2OCHO are also discussed.
Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the ...complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA), and benzoyl peroxide (BZP)) with dissolved SO2. Results show that due to the presence of the hydroperoxyl group in their structures, MHP and PAA are susceptible to forming inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability of PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within the pH 1–10 and 240–340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH3 and -C6H5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions.
Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the ...complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA), and benzoyl peroxide (BZP)) with dissolved SO.sub.2 . Results show that due to the presence of the hydroperoxyl group in their structures, MHP and PAA are susceptible to forming inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability of PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within the pH 1-10 and 240-340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH.sub.3 and -C.sub.6 H.sub.5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions.
The kinetics of the gas-phase atmospheric reaction of t-butanol with OH radicals is computationally studied using the CCSD(T)/aug-cc-pVTZ//M06-2X/6–311++G(d,p) level of calculation. The rate ...coefficients are evaluated for a wide temperature range of 250–1200 K and the calculated rate coefficient value of 0.83×10−12cm3molecule−1s−1 at 298K is in close agreement with experimental results. The H-abstraction from the –CH3 group is predicted to be the main reaction channel. A weak negative temperature dependence of rate coefficient is observed in 250–300 K. The study also highlighted the possibility of re-generation of OH radicals at higher temperature. The ozone formation potential of t-butanol in the troposphere has also been estimated and discussed.
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•Theoretical study is performed on the kinetics and mechanism of the reaction of tert-butanol with OH radical.•CCSD(T) and conventional transition state theory are used for kinetic modeling.•Important reaction channels are identified for this reaction.•Rate coefficients are estimated in a wide temperature range of 250–1200 K.•Ozone formation potential of tert-butanol is reported.
