Photolysis of multifunctional carbonyl compounds under natural irradiation at EUPHORE: Fid-Bau Portal

Photolysis of multifunctional carbonyl compounds under natural irradiation at EUPHORE

Tomas, A. / Aslan, L. / Muñoz, A. / Ródenas, M. / Vera, T. / Borrás, E. / Coddeville, P. / Fittschen, C.

Abstract Photolysis is one the main drivers in atmospheric chemistry. Volatile organic compounds that bear one or more carbonyl functions can absorb UV light between 295 nm and 450 nm, enabling them to possibly photolyze in the atmosphere. Yet, very few data are available regarding the impact of such photolysis processes on the fate of multifunctional carbonyls. In the present work, we investigated the photodissociation of one α-diketone and three hydroxyketones under real sunlight at the European Photoreactor EUPHORE. The obtained photolysis frequencies normalized by NO2 photolysis were: 2,3-pentanedione (PTD): (3.4 ± 0.6) × 10⁻², 4-hydroxy-4-methyl-2-pentanone (4H4M2P): (6.2 ± 2.9) × 10⁻⁴, 3-hydroxy-3-methyl-2-butanone (3H3M2B): (8.2 ± 4.9) × 10⁻⁴, and 4-hydroxy-3-hexanone (4H3H): (5.1 ± 3.0) × 10⁻⁴. These ratios represent the first data for three of them, to our knowledge. Reaction products were also investigated and carbon balances of 70–100% in the gas-phase have been obtained. A photolysis reaction mechanism is proposed for 4H3H for the first time, based on the observed products. Atmospheric lifetimes span between 39 min for PTD to 1–2 days for hydroxyketones. The present work shows that photolysis of multi-oxygenated VOCs may be significant and needs to be taken into account in atmospheric chemistry models where it represents an additional source of radicals.

Highlights • Atmospheric photolysis of hydroxyketones may be significant. • Molecular structure is relevant for determining photolysis importance. • Detailed photolysis mechanisms are proposed for the first time. • 2,3-pentanedione photolysis mechanism investigated.