ATMOCHEM - Reactivity of Oxygenated Volatile Organic Compounds (ROVOC): Esters

• Applicant: Dr. Ian Barnes
• Subject Area: Atmospheric Science
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 83085079

Oxygenated volatile organic compounds (OVOCs) are omnipresent in the atmosphere. Esters (alkyl alkanoates, e.g. RC(O)OR, R = alkyl groups) are an important class of OVOC with both natural and anthropogenic sources. Esters made up of long chain carboxylic acids are the main constituents of animal- and plant-derived waxes and they also occur naturally in fruits and flowers. Various types of esters are used extensively by industry as solvents in chemical processing. The quest for renewable fuels has seen an increase in the use of biodiesel fuels, which typically consist of methyl and ethyl esters of fatty acids. Esters can also be produced in situ in the atmosphere from, for example, the oxidation of ethers. Few measurements of esters in the atmosphere have been made but those measurements, which have been made, confirm the presence of substantial levels of esters in the atmosphere.Investigations on the atmospheric chemistry of esters to date have been limited to temperature dependent studies of the OH radical kinetics of a number of linear and branched alkyl acetates and room temperature studies of the products from the OH radical or Cl-atom initiated oxidation of a few of these acetates. Studies on methylacetate have shown that the product yield distribution is very temperature dependent. Although this limited set of data has been used been used to improve the structure-activity relationship (SAR) for alkyl esters at 298 K it is clear that there is a definite need for further refine of the SAR for esters particularly with respect to temperature dependence.The project has the overall aim of improving the kinetic, product and mechanistic database for the reactions of OH radicals with a variety of esters as a function of temperature over the range 225-372 K and will use this information to further develop and refine the SAR for esters. The project will consist of the following components: i) determination of OH rate coefficients using absolute and relative methods as a function of temperature; ii) determination of the products of the reactions as a function of temperature and O2 partial pressure; iii) construction of explicit and simplified reaction mechanisms for models; iv) development of SAR for a wider range of ester types applicable over the temperature range 225-372 K.

• DFG Programme: Research Grants
• International Connection: France
• Participating Person: Dr. Abdelwahid Mellouki