Impact of pyruvic acid photolysis on acetaldehyde and peroxy radical formation in the boreal forest: theoretical calculations and model results

Abstract. Based on the first measurements of gas-phase pyruvic acid (CH3C(O)C(O)OH) in boreal forest, we derive effective emission rates and compare them with monoterpene over diel cycle. Using a data-constrained box model, determine impact photolysis formation acetaldehyde (CH3CHO) peroxy radicals CH3C(O)O2 HO2 during an autumn campaign forest. The results are dependent quantum yield (φ) mechanism photodissociation fate likely major product, methylhydroxy carbene (CH3COH). With investigate two different scenarios which follow present IUPAC (IUPAC Task Group Atmospheric Chemical Kinetic Data Evaluation, 2021) recommendations φ = 0.2 (at 1 bar air), main products (60 %) + CO2 35 % C–C bond fission to form HOCO CH3CO (scenario A). In second scenario (B), vibrationally hot CH3COH (and CO2) represents dissociation pathway at longer wavelengths (∼ 75 ∼ 25 contribution from shorter wavelengths). 2 vary between and, based our theoretical calculations, allow thermalized react O2 (forming radicals) undergo acid-catalysed isomerization CH3CHO. When constraining measured mixing ratios independent model scenario, find that is dominant source CH3CHO 70 90 total production rate. We also acetylperoxy radical, contributions varying 20 60 choice formed. enhanced, mainly via CH3O2. elevated concentration result significant increases modelled CH3C(O)OOH, CH3OOH, HCHO, H2O2.