Tropospheric photooxidation of methyl methacrylate: product distribution at 298 K

MARÍA B. BLANCO, IAN BARNES, PETER WIESEN , MARIANO A. TERUEL.

Conferencia; ATMOSPHERIC CHEMICAL MECHANISMS; 2014

Methyl methacrylate (CH2=C(CH3)C(O)OCH3, MMA) is listed as a high (H) production (P) volume (V) chemical in the OECD (Organization for Economic Co-operation and Development) integrated HPV database. Many different kinds of esters including MMA have been measured in ambient air. Emissions of these esters to the atmosphere can occur during their production, processing, storage and disposal and once in the atmosphere they will be subject to photodegradation mainly by OH and also NO3 and O3, and in certain environments by Cl atoms. In order to assess the contribution of the atmospheric photooxidation of methacrylate esters to the formation of photochemical oxidants and SOA formation in urban environments, detailed kinetic and mechanistic information on their tropospheric gas-phase degradation pathways are required. To this end, the OH radical and Cl atom initiated photodegradation of MMA have been investigated in a 1080 L chamber at 298 K and atmospheric pressure of synthetic air by in situ FTIR spectroscopy. The main products observed in the OH reaction were methyl pyruvate together with formaldehyde as a co-product from the C1-C2 bond cleavage channel of the intermediate 1,2-hydroxyalkoxy radical, formed by addition of OH to the terminal carbon of the double bond which is designated C1. For the Cl atom reaction the products identified were methyl pyruvate together with formyl chloride as a co-product and chloroacetone together with formaldehyde. The results show that the fate of the intermediate 1,2-chloroalkoxy radical involves not only cleavage of the C1-C2 bond but also quite substantial cleavage of the C2-C3 bond where C2 is the internal carbon of the double bond and C3 is the carbonyl carbon.