Simulation chamber studies of the atmospheric oxidation of 2-Methyl-3-Buten-2-ol: Reaction with hydroxyl radicals and ozone under a variety of conditions

This article presents a complete study of the diurnal chemical reactivity of the biogenic volatile organic compound (BVOC), 2-methyl-3-buten-2-ol (MBO) in the troposphere. Reactions of MBO with OH and with ozone were studied to analyse the respective parts of both processes in the global budget of MBO atmospheric reactivity. They were investigated under controlled conditions for pressure (atmospheric pressure) and temperature (298±2 K) using three complementary European simulation chambers. Reaction with OH radicals was studied in the presence of and in the absence of NO_x. The kinetic study was carried out by relative rate study using isoprene as a reference. The rate constant found for this reaction was ^kMBO+OH = (5.6 ± 0.6) × 10^-11 molecule^-1 cm³ s^-1. FTIR spectroscopy, DNPH- and PFBHA-derivatisation analyses were performed for reactions with both OH radicals and ozone. In both reactions, the hydroxycarbonyl compound, 2-hydroxy-2-methylpropanal (HMPr) was positively identified and quantified, with a yield of R_HMPr = 0.31± 0.11 in the reaction with OH, and a yield of R_HMPr 0.43 ± 0.12 and 0.84±0.08 in the reaction with ozone under dry (HR<1%) and humid conditions (HR=20%-30%). A primary production of two other carbonyl compounds, acetone R_acetone = 0.39 ± 0.22, and formaldehyde R_HCHO = 0.44 ± 0.05 was found in the case of the dry ozonolysis experiments. Under humid conditions, only formaldehyde was co-produced with HMPr as a primary carbonyl compound, with a yield of R_HCHO = 0.55 ± 0.03. For the reaction with OH, three other carbonyl compounds were detected, acetone R_acetone = 0.67 ± 0.05, formaldehyde R_HCHO = 0.33 ± 0.08 and glycolaldehyde R_{glycolaldehyde} = 0.78 ± 0.20. In addition some realistic photo-oxidation experiments were performed to understand in an overall way the transformations of MBO in the atmosphere. The realistic photo-oxidation experiments were conducted in the EUPHORE outdoor simulation chamber. It was found that this compound is a weak secondary aerosol producer (less than 1% of the carbon balance). But it was confirmed that it is a potentially significant source of acetone, Δ[Acetone]/ Δ[MBO]=0.45. With our experimental conditions ([MBO]₀ =200 ppb, [NO]o=50 ppb), an ozone yield of Δ[O₃]/ Δ[MBO]=1.05 was found.