Kinetic Study of the OH + Glyoxal Reaction: Experimental Evidence and Quantification of Direct OH Recycling

Abstract

The kinetics of the OH + glyoxal, (HCO)2, reaction have been studied in N2 and N2/O2 bath gas from 5-80 Torr total pressure and 212-295 K, by monitoring the OH decay via laser induced fluorescence (LIF) in excess (HCO)2. The following rate coefficients, kOH+(HCO)2 = (9.7 ± 1.2), (12.2 ± 1.6), and (15.4 ± 2.0) × 10(-12) cm(3) molecule(-1) s(-1) (where errors represent a combination of statistical errors at the 2σ level and estimates of systematic errors) were measured in nitrogen at temperatures of 295, 250, and 212 K, respectively. Rate coefficient measurements were observed to be independent of total pressure but decreased following the addition of O2 to the reaction cell, consistent with direct OH recycling. OH yields, ΦOH, for this reaction were quantified experimentally for the first time as a function of total pressure, temperature, and O2 concentration. The experimental results have been parametrized using a chemical scheme where a fraction of the HC(O)CO population promptly dissociates to HCO + CO, the remaining HC(O)CO either dissociates thermally or reacts with O2 to give CO2, CO, and regenerate OH. A maximum ΦOH of (0.38 ± 0.02) was observed at 212 K, independent of total pressure, suggesting that ∼60% of the HC(O)CO population promptly dissociates upon formation. Qualitatively similar behavior is observed at 250 K, with a maximum ΦOH of (0.31 ± 0.03); at 295 K, the maximum ΦOH decreased further to (0.29 ± 0.03). From the parametrization, an OH yield of ΦOH = 0.19 is calculated for 295 K and 1 atm of air. It is shown that the proposed mechanism is consistent with previous chamber studies. While the fits are robust, experimental evidence suggests that the system is influenced by chemical activation and cannot be fully described by thermal rate coefficients. The atmospheric implications of the measurements are briefly discussed.

Atmospheric chemistry, sources and sinks of carbon suboxide, C<sub>3</sub>O<sub>2</sub>

“…The IR and UV spectra of carbon suboxide were measured, showing good agreement with earlier work (Bayes, 1961;Long et al, 1954;Miller and Fateley, 1964;Vander Auwera et al, 1991). The atmospheric photolysis rate constants obtained from the UV spectrum and assuming a photo-dissociation quantum yield of unity range from 1 × 10 −6 to 4.0 × 10 −6 s −1 , depending on the altitude, for a zenith angle of 50 • .…”

“…The resulting peroxy radical INT8, OCC(OO q )COOH, has a fairly mobile hydrogen atom, which can temporarily migrate to the oxygen radical site; this H shift was calculated to be endothermic by only 11 to 12 kcal mol −1 . The resulting hydroperoxide acyloxy radical, OCC(OOH)C(O q )O, is not an energetic minimum at the chosen level of theory, spontaneously reforming the carboxylic acid peroxy radical; this is contrary to similar reactions in aliphatic carboxylic acid atmospheric oxidation where CO 2 is preferentially eliminated (Lockhart et al, 2013;da Silva, 2010). All reactions of the transient hydroperoxide examined, including CO 2 elimination and cyclization, appear to have relatively high barriers exceeding 20 kcal mol −1 relative to the peroxy radical.…”

“…2.1 Chemicals C 3 O 2 was prepared by the low-temperature dehydration of malonic acid by P 4 O 10 in a similar manner as described previously (Diels and Meyerheim, 1907;Long et al, 1954), and diluted with nitrogen bath gas (Westfalen, N 2 5.0) to atmospheric pressure, yielding 20.0 to 26.7 mbar C 3 O 2 in 1000 mbar N 2 . No efforts were undertaken to increase the yield of C 3 O 2 by careful drying of the reactants as performed previously (Diels and Lalin, 1908) as only a small partial pressure was needed.…”

Glyoxal measurement with a proton transfer reaction time of flight mass spectrometer (PTR‐TOF‐MS): characterization and calibration

“…In unpolluted regions, with low NOx mixing ratios and high amounts of VOCs glyoxal photolysis may contribute to the regeneration of HOx (HO + HO 2 ) in the troposphere. These conditions occur over tropical rainforests, where high emissions of isoprene may suppress ambient OH levels if recycling mechanisms such as via glyoxal photolysis did not occur . Additionally, glyoxal contributes to the formation of secondary organic aerosol (SOA) and cloud droplets, which in turn affect climate and air quality …”

Evaluation of OH and HO<sub>2</sub> concentrations and their budgets during photo-oxidation of 2-methyl-3-butene-2-ol (MBO) in the atmospheric simulation chamber SAPHIR

“…Contemporary, other trace gases have been investigated as the results from the isoprene studies show that OH recycling through isoprene-RO 2 , alone, is not sufficient to explain the OH concentrations observed in the field. Chamber and laboratory studies on methacrolein (MACR) Fuchs et al, 2014), methyl vinyl ketone (MVK) (Praske et al, 2015), isoprene hydroxy hydroperoxide (D' Ambro 10 et al, 2017) and glyoxal (Feierabend et al, 2008;Lockhart et al, 2013), important products from the oxidation of isoprene by OH, also have shown new OH recycling paths as predicted by theory (Peeters et al, 2009;da Silva, 2010;Setokuchi, 2011;da Silva, 2012). Further laboratory studies also have discovered OH radical recycling in the bimolecular reaction of HO 2 with acyl peroxy radicals which was previously considered to be a radical termination reaction only Groß et al, 2014;Praske et al, 2015).…”