Rate Constant and Branching Ratio for the Reactions of the Ethyl Peroxy Radical with Itself and with the Ethoxy Radical

Abstract. Alkenes are oxidized rapidly in the atmosphere by addition of OH and subsequently O2 leading to the formation of β-hydroxy peroxy radicals. These peroxy radicals react with NO to form β-hydroxy nitrates with a branching ratio α. We quantify α for C2–C8 alkenes at 295 K ± 3 and 993 hPa. The branching ratio can be expressed as α = (0.045 ± 0.016) × N − (0.11 ± 0.05) where N is the number of heavy atoms (excluding the peroxy moiety), and listed errors are 2σ. These branching ratios are larger than previously reported and are similar to those for peroxy radicals formed from H abstraction from alkanes. We find the isomer distributions of β-hydroxy nitrates formed under NO-dominated peroxy radical chemistry to be different than the isomer distribution of hydroxy hydroperoxides produced under HO2-dominated peroxy radical chemistry. Assuming unity yield for the hydroperoxides implies that the branching ratio to form β-hydroxy nitrates increases with substitution of RO2. Deuterium substitution enhances the branching ratio to form hydroxy nitrates in both propene and isoprene by a factor of ~ 1.5. The role of alkene chemistry in the Houston region is re-evaluated using the RONO2 branching ratios reported here. Small alkenes are found to play a significant role in present-day oxidant formation more than a decade (2013) after the 2000 Texas Air Quality Study identified these compounds as major contributors to photochemical smog in Houston.

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Removal of Refractory Organic Compounds Using Peroxy Radical and Ozone Reaction in Aqueous Solution

Materials Science Forum ◽

10.4028/www.scientific.net/msf.569.33 ◽

2008 ◽

Vol 569 ◽

pp. 33-36

Author(s):

Jong Tae Jung ◽

Jong Oh Kim ◽

Bum Gun Kwon ◽

Dong Ha Song

Keyword(s):

Aqueous Solution ◽

Reaction Time ◽

Humic Acid ◽

Hydroxyl Radical ◽

Organic Compounds ◽

Acid Concentration ◽

Rate Constant ◽

Reaction Rate ◽

Peroxy Radical ◽

Reaction Rate Constant

This study was conducted to evaluate the treatment performance of the system using peroxy radical/ozone reaction for refractory organic compounds removal in aqueous solution. The effect of initial humic acid concentration was conducted under the conditions of humic acid concentration 10 mg/L, 30 mg/L, 50 mg/L and 100 mg/L. Reaction rate constant (k) in 30 mg/L of humic acid concentration was higher than that of humic acid concentration 10 mg/L, 50 mg/L amd 100 mg/L. However, it decreased over the range of 30 mg/L of humic acid concentration due to the action of internal filter of humic acid itself. Reaction rate constant (k) in the initial 20 minute of reaction time was accelerated by decreasing hydraulic retention time (HRT). This may be ascribed to increase the reaction time between peroxy radical and ozone. pH is a key for both ozone stability and TiO2 surface property in aqueous solution. Reaction rate constant (k) of acid solution on pH variation was smaller compared to that of neutral or basic circumstances because ozone decomposes easily into hydroxyl radicals in neutral or basic solution. At reaction rate constant (k) for humic acid degradation in each unit process, peroxy radical/ozone combined system was higher than that of ozone only due to the effective production of hydroxyl radical. An obvious difference between ozone and peroxy radical/ozone is the consequence of hydroxyl radical produced by the reaction of ozone molecules and peroxy radicals.

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Reassessing the atmospheric oxidation mechanism of toluene

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1705463114 ◽

2017 ◽

Vol 114 (31) ◽

pp. 8169-8174 ◽

Cited By ~ 62

Author(s):

Yuemeng Ji ◽

Jun Zhao ◽

Hajime Terazono ◽

Kentaro Misawa ◽

Nicholas P. Levitt ◽

...

Keyword(s):

Quantum Chemical Calculations ◽

Quantum Chemical ◽

Branching Ratio ◽

Oxidation Mechanism ◽

Peroxy Radical ◽

Chemical Oxidation ◽

Urban Environments ◽

Photochemical Oxidation ◽

Peroxy Radicals ◽

Toluene Oxidation

Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O2 to form the cresol proceeds with a smaller barrier than O2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.

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