Hydrolysis of Formyl Fluoride Catalyzed by Sulfuric Acid and Formic Acid in the Atmosphere

Formyl fluoride (HFCO) is an important atmospheric molecule, and its reaction with the OH radical is an important pathway when degradation of HFCO is considered in earth’s troposphere. Here, we study the hydrolysis of formyl fluoride (HFCO + H2O) with sulfuric acid (H2SO4) and formic acid (HCOOH) acting as catalysts by utilizing M06-2X, CCSD­(T)-F12a, and conventional transitional state theory with Eckart tunneling to explore the atmospheric impact of the above-said hydrolysis reactions. Our calculated results show that H2SO4 has a remarkably catalytic role in the gas-phase hydrolysis of HFCO, as the energy barriers of the HFCO + H2O reaction are reduced from 39.22 and 41.19 to 0.26 and −0.63 kcal/mol with respect to the separate reactants, respectively. In addition, we also find that H2SO4 can significantly accelerate the decomposition of FCH­(OH)2 into hydrogen fluoride (HF) and HCOOH. This is because while the barrier height for the unimolecular decomposition of FCH­(OH)2 into HF and HCOOH is 31.63 kcal/mol, the barrier height for the FCH­(OH)2 + H2SO4 reaction is predicted to be −5.99 kcal/mol with respect to separate reactants. Nevertheless, the comparative relative rate analysis shows that the reaction between HFCO and the OH radical is still the most dominant pathway when the tropospheric degradation of HFCO is taken into account and that the gas-phase hydrolysis of HFCO may only occur with the help of H2SO4 when the atmospheric concentration of OH is about 101 molecules cm–3 or less. Having an understanding from the present study that the gas-phase hydrolysis of HFCO in the presence of H2SO4 has very limited role possibly in the absence of sunlight, we also prefer here to emphasize that the HFCO + H2O + H2SO4 reaction may occur on the surface of secondary organic aerosols for the formation of HCOOH

Important Routes for Methanediol Formation by Formaldehyde Hydrolysis Catalyzed by Iodic Acid and for the Contribution to an Iodic Acid Sink by the Reaction of Formaldehyde with Iodic Acid Catalyzed by Atmospheric Water

Methanediol formed by the hydrolysis of formaldehyde is an important intermediate in the formation of formic acid in the atmosphere. However, the formation of methanediol by the direct reaction of formaldehyde (HCHO) with water (H2O) is not feasible in the gas phase in the atmosphere due to the very high enthalpy of activation at 0 K for the HCHO + H2O reaction. Here, by using quantum chemical methods and reaction rate theory, we report a new mechanistic route for the iodic acid-catalyzed gas-phase hydrolysis of formaldehyde. The present findings show that iodic acid serves as an excellent catalyst in this reaction, decreasing the enthalpy of activation at 0 K from 36.01 kcal/mol for the HCHO + H2O reaction to −13.28 kcal/mol for the HCHO + H2O + HIO3 reaction with respect to the separate reactants. Additionally, the calculation results also show that water can catalyze the HCHO + HIO3 reaction, decreasing the enthalpy of activation at 0 K for the HCHO + HIO3 reaction from 2.96 to −10.00 kcal/mol. The calculated kinetics results reveal that the gas-phase hydrolysis of formaldehyde catalyzed by iodic acid can make a substantial contribution to the sink of formaldehyde and the formation of methanediol below 260 K. The reaction of formaldehyde with iodic acid catalyzed by water dominates over the HIO3 + OH reaction under full atmospheric conditions. The present findings are expected have broad implications for understanding the formation of methanediol and the sink of formaldehyde and iodic acid in the atmosphere

MOESM1 of Plant leaves for wrapping zongzi in China: an ethnobotanical study

Additional file 1: Table S1. The investigation areas (county level) where people are familiar with the functions of ZLs

Quantitative Kinetics of HO₂ Reactions with Aldehydes in the Atmosphere: High-Order Dynamic Correlation, Anharmonicity, and Falloff Effects Are All Important

Kinetics provides the fundamental parameters for elucidating sources and sinks of key atmospheric species and for atmospheric modeling more generally. Obtaining quantitative kinetics in the laboratory for the full range of atmospheric temperatures and pressures is quite difficult. Here, we use computational chemistry to obtain quantitative rate constants for the reactions of HO2 with HCHO, CH3CHO, and CF3CHO. First, we calculate the high-pressure-limit rate constants by using a dual-level strategy that combines conventional transition state theory using a high level of electronic structure wave function theory with canonical variational transition state theory including small-curvature tunneling using density functional theory. The wave-function level is beyond-CCSD(T) for HCHO and CCSD(T)-F12a (Level-A) for XCHO (X = CH3, CF3), and the density functional (Level-B) is specifically validated for these reactions. Then, we calculate the pressure-dependent rate constants by using system-specific quantum RRK theory (SS-QRRK) and also by an energy-grained master equation. The two treatments of the pressure dependence agree well. We find that the Level-A//Level-B method gives good agreement with CCSDTQ(P)/CBS. We also find that anharmonicity is an important factor that increases the rate constants of all three reactions. We find that the HO2 + HCHO reaction has a significant dependence on pressure, but the HO2 + CF3CHO reaction is almost independent of pressure. Our findings show that the HO2 + HCHO reaction makes important contribution to the sink for HCHO, and the HO2 + CF3CHO reaction is the dominant sink for CF3CHO in the atmosphere

New Reactions for the Formation of Organic Nitrate in the Atmosphere

Organic nitrates make an important contribution to the formation of secondary organic aerosols, but the formation mechanisms of organic nitrates are not fully understood at the molecular level. In the present work, we explore a new route for the formation of organic nitrates in the reaction of formaldehyde (HCHO) with nitric acid (HNO3) catalyzed by water (H2O), ammonia (NH3), and dimethylamine ((CH3)2NH) using theoretical methods. The present results using CCSD­(T)-F12a/cc-pVTZ-F12//M06-2X/MG3S unravel that dimethylamine has a stronger catalytic ability in the reaction of HCHO with HNO3, reducing the barrier by 21.97 kcal/mol, while water and ammonia only decrease the energy barrier by 7.35 and 13.56 kcal/mol, respectively. In addition, the calculated kinetics combined with the corresponding concentrations of these species show that the HCHO + HNO3 + (CH3)2NH reaction can compete well with the naked HCHO + HNO3 reaction at 200–240 K, which may make certain contributions to the formation of organic nitrates under some atmospheric conditions

Atmospheric Chemistry of Criegee Intermediates: Unimolecular Reactions and Reactions with Water

Criegee intermediates are produced in the ozonolysis of unsaturated hydrocarbons in the troposphere, and understanding their fate is a prerequisite to modeling climate-controlling atmospheric aerosol formation. Although some experimental and theoretical rate data are available, they are incomplete and partially inconsistent, and they do not cover the tropospheric temperature range. Here, we report quantum chemical rate constants for the reactions of stabilized formaldehyde oxide (CH2OO) and acetaldehyde oxide (syn-CH3CHOO and anti-CH3CHOO) with H2O and for their unimolecular reactions. Our results are obtained by combining post-CCSD­(T) electronic structure benchmarks, validated density functional theory potential energy surfaces, and multipath variational transition state theory with multidimensional tunneling, coupled-torsions anharmonicity, and high-frequency anharmonicity. We consider two different types of reaction mechanisms for the bimolecular reactions, namely, (i) addition-coupled hydrogen transfer and (ii) double hydrogen atom transfer (DHAT). First, we show that the MN15-L exchange-correlation functional has kJ/mol accuracy for the CH2OO + H2O and syn-CH3CHOO + H2O reactions. Then we show that, due to tunneling, the DHAT mechanism is especially important in the syn-CH3CHOO + H2O reaction. We show that the dominant pathways for reactions of Criegee intermediates depend on altitude. The results we obtain eliminate the discrepancy between experiment and theory under those conditions where experimental results are available, and we make predictions for the full range of temperatures and pressures encountered in the troposphere and stratosphere. The present results are an important cog in clarifying the atmospheric fate and oxidation processes of Criegee intermediates, and they also show how theoretical methods can provide reliable rate data for complex atmospheric processes

Quantitative Kinetics of the Reaction between CH₂OO and H₂O₂ in the Atmosphere

Criegee intermediates (CIs) are generated from the ozonolysis of unsaturated hydrocarbons in the atmosphere. They have an important role in determining the implications of atmospheric bimolecular reactions with other atmospheric species. The reaction between CH2OO and H2O2 plays a crucial role in understanding how CIs impact the HOx budget in the atmosphere. The reaction mechanism and kinetics are critical to atmospheric modeling, which is a prominent challenge in present-day climate change modeling. This is particularly true for bimolecular reactions that involve complex reaction sequences. Here, we report the mechanism and quantitative kinetics of the CH2OO + H2O2 reaction by using a novel dual-level strategy that contains W3X-L//CCSD(T)-F12a/cc-pVTZ-F12 for the transition state theory and M11-L/MG3S functional method for direct dynamics calculations using canonical variational transition state theory with small-curvature tunneling to obtain both recrossing effects and tunneling. The present work shows that the CH2OO + H2O2 reaction has a negative temperature dependency with the decrease in the rate constant of CH2OO + H2O2 from 1.31 × 10–13 cm3 molecule–1 s–1 to 3.80 × 10–14 cm3 molecule–1 s–1 between 200 and 350 K. The calculated results also show that the CH2OO + H2O2 reaction can have an impact on the H2O2 profile under certain atmospheric conditions. The present findings should have implications for the quantitative kinetics of Criegee intermediates with other hydroperoxides

Rapid Atmospheric Reactions between Criegee Intermediates and Hypochlorous Acid

Hypochlorous acid (HOCl) is a paramount compound in the atmosphere due to its significant contribution to both tropospheric oxidation capacity and ozone depletion. The main removal routes for HOCl are photolysis and the reaction with OH during the daytime, while these processes are unimportant during the nighttime. Here, we report the rapid reactions of Criegee intermediates (CH2OO and anti/syn-CH3CHOO) with HOCl by using high-level quantum chemical methods as the benchmark; their accuracy is close to coupled cluster theory with single, double, and triple excitations and quasiperturbative connected quadruple excitations with a complete basis limit by extrapolation [CCSDT­(Q)/CBS]. Their rate constants have been calculated by using a dual-level strategy; this combines conventional transition state theory calculated at the benchmark level with variational transition state theory with small-curvature tunneling by a validated density functional method. We find that the introduction of the methyl group into Criegee intermediates not only affects their reactivities but also exerts a remarkable influence on anharmonicity. The calculated results uncover that anharmonicity increases the rate constants of CH2OO + HOCl by a factor of 18–5, while it is of minor importance in the anti/syn-CH3CHOO + HOCl reaction at 190–350 K. The present findings reveal that the loose transition state for anti-CH3CHOO and HOCl is a rate-determining step at 190–350 K. We also find that the reaction of Criegee intermediates with HOCl contributes significantly to the sink of HOCl during the nighttime in the atmosphere

Kinetics of Sulfur Trioxide Reaction with Water Vapor to Form Atmospheric Sulfuric Acid

Although experimental methods can be used to obtain the quantitative kinetics of atmospheric reactions, experimental data are often limited to a narrow temperature range. The reaction of SO3 with water vapor is important for elucidating the formation of sulfuric acid in the atmosphere; however, the kinetics is uncertain at low temperatures. Here, we calculate rate constants for reactions of sulfur trioxide with two water molecules. We consider two mechanisms: the SO3···H2O + H2O reaction and the SO3 + (H2O)2 reaction. We find that beyond-CCSD(T) contributions to the barrier heights are very large, and multidimensional tunneling, unusually large anharmonicity of high-frequency modes, and torsional anharmonicity are important for obtaining quantitative kinetics. We find that at lower temperatures, the formation of the termolecular precursor complexes, which is often neglected, is rate-limiting compared to passage through the tight transition states. Our calculations show that the SO3···H2O + H2O mechanism is more important than the SO3 + (H2O)2 mechanism at 5–50 km altitudes. We find that the rate ratio between SO3···H2O + H2O and SO3 + (H2O)2 is greater than 20 at altitudes between 10 and 35 km, where the concentration of SO3 is very high