Abstract
Abstract. The OH-radical-initiated oxidation of 3-methyl-3-penten-2-one and 4-methyl-3-penten-2-one was investigated in two atmospheric simulation chambers at 298±3 K and 990±15 mbar using long-path FTIR spectroscopy. The rate coefficients of the reactions of 3-methyl-3-penten-2-one and 4-methyl-3-penten-2-one with OH radicals were determined to be (6.5±1.2)×10-11 and (8.1±1.3)×10-11 cm3molecule-1s-1, respectively. To enlarge the kinetics data pool the rate coefficients of the target species with Cl atoms were determined to be (2.8±0.4)×10-10 and (3.1±0.4)×10-10 cm3molecule-1s-1, respectively. The mechanistic investigation of the OH-initiated oxidation focuses on the RO2+NO reaction. The quantified products were acetoin, acetaldehyde, biacetyl, CO2 and peroxyacetyl nitrate (PAN) for the reaction of 3-methyl-3-penten-2-one with OH radicals and acetone, methyl glyoxal, 2-hydroxy-2-methylpropanal, CO2 and peroxyacetyl nitrate (PAN) for the reaction of 4-methyl-3-penten-2-one with OH, respectively. Based on the calculated product yields an upper limit of 0.15 was determined for the yield of RONO2 derived from the OH reaction of 4-methyl-3-penten-2-one. By contrast, no RONO2 formation was observed for the OH reaction of 3-methyl-3-penten-2-one. Additionally, a simple model is presented to correct product yields for secondary processes.
Highlights
The α,β-unsaturated ketones are a particular class of oxygenated volatile organic compounds (OVOCs) emitted either from biogenic and/or anthropogenic sources or generated in the oxidation of airborne VOCs in the atmosphere
Besides the first determination of the rate coefficient for the reaction of OH radicals with 3M3P2, we report kinetic data for Cl atom reactions
It is generally accepted that OH radical and Cl atom reactions of OVOCs proceed via H atom abstraction or addition to the C=C double bond, in the case of unsaturated organic species
Summary
The α,β-unsaturated ketones are a particular class of oxygenated volatile organic compounds (OVOCs) emitted either from biogenic and/or anthropogenic sources or generated in the oxidation of airborne VOCs in the atmosphere. In order to correct the formation yields of products formed in target reactions within complex experimental systems it is quite common to use the Tuazon formalism (Tuazon et al, 1986) This is based on the assumption that reaction products are subsequently consumed in secondary processes like photolysis, wall loss and oxidation by OH radicals. Their formation yields in the target reactions are underestimated when determined from plotting the formed product against the consumed compound of interest, and the yields increase when corrected. The study investigates the contribution of the OH-initiated oxidation of both 3M3P2 and 4M3P2 to the formation of NOx reservoir species, like peroxyacetyl nitrate (PAN), in the atmosphere.
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