A continuous stirred tank reactor investigation of the gas‐phase reaction of hydroxyl radicals and toluene

Abstract

A continuous stirred tank reactor (CSTR) was used to study the gas-phase reaction between H O and toluene. HO' was generated by the in situ photolysis of nitrous acid.Flow reactor operation at steady-state conditions with a residence time of 20 min allowed investigation of primary and very rapid secondary reactions. CSTR and batch reactor experiments were also performed with selected products. Both gas-phase and aerosol products were identified by chromatography and mass spectroscopy, with total product yields between 55 and 75% of reacted carbon. Toluene reaction products included cresols, nitrocresols, nitrotoluenes, 3,5-dinitrotouluene, benzaldehyde, benzyl nitrate, nitrophenols, methyl-p-benzoquinone, glyoxal, methylglyoxal, formaldehyde, methyl nitrate, PAN, and CO. The fraction of HO' methyl hydrogen abstraction was calculated to be 0.13 2 0.04. The ratio of reaction rate constants for nitrotoluene versus cresol formation from the HO-adduct was calculated to be about 3.3 x lo4. Also, the ratio of cresol formation versus 0, addition to the HO-adduct was estimated to be 20.5 for atmospheric conditions. Comparisons of these measurements with previous values and the implications with respect to photochemical kinetics modeling of the atmosphere are discussed.

Reassessing the atmospheric oxidation mechanism of toluene

“…The yield of 11.3% for benzaldehyde determined in our present work is in agreement with the previous studies reporting a range of 5 to 12% (9,11,12,18). We determined a lower limit of 47.9% for the total branching ratio of the cresol pathway (pathway I), including those from the combined formation of cresols and dihydroxymethylbenzenes.…”

“…However, the detailed chemical mechanism of toluene oxidation in the atmosphere remains uncertain (4,5). Oxidation of toluene is initiated by the hydroxyl radical (OH): the initial OH−toluene reaction results in minor H abstraction (about 10%) and major OH addition (about 90%) (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The H-abstraction pathway leads to the formation of benzaldehyde, whose oxidative pathway is well established (4,5).…”

Low temperatures enhance organic nitrate formation: evidence from observations in the 2012 Uintah Basin Winter Ozone Study

“…Methanol and ethanol are presumed to have zero nitrate yield, since their reactions with O 2 after hydrogen abstraction to form carbonyls and HO 2 are dominant. Finally, the nitrate yields for aromatics were set to 1 % in this analysis, following the yield of benzyl nitrate from toluene oxidation (Gery et al, 1985;Atkinson and Aschmann, 1989;Atkinson, 1994). It is noted that even by assuming an upperlimit nitrate yield of 0.35, the contribution from aromatic compounds to alkyl nitrate production is minor (14 %) relative to the production from alkanes.…”

Quantifying the reactive uptake of OH by organic aerosols in a continuous flow stirred tank reactor

“…The CFSTR has been previously used to study aerosol formation [21][22][23] as well as gas phase reactions. 24,25 Fewer studies have applied CFSTR's to heterogeneous reactions on aerosol particles. 26,27 In these previous studies, the rate of a heterogeneous or homogeneous reaction inside a CFSTR was obtained by measuring the difference between the reactant concentrations entering and exiting the reaction volume divided by the residence time, once the CFSTR has reached steady state.…”