Multivariate relative rate measurements of reactions between volatile organic compounds (VOCs) and atmospheric radicals

Knowledge of the reactions between VOCs and atmospheric radicals and oxidants is fundamental to understanding atmospheric chemistry and the formation of air pollution in urban environments. This work describes the development of a new experimental technique for the simultaneous measurement of gas-phase rate coefficients for reactions between multiple VOCs and different atmospheric radicals. The technique is based on the traditional relative rate approach and succeeds in markedly increasing the rate of throughput of target reactions; an improvement necessary when considering the vast number of organic compounds observed in the atmosphere for which experimental oxidation data are not available. New rate coefficients are derived using a suite of the available kinetic literature as reference reactions to calibrate the results over a range of reactivity, thereby reducing the reliance on any single rate coefficient value. This new multivariate method was applied to mixtures containing multiple VOCs with a range in functionalities and under different experimental conditions. Two different atmospherically relevant radicals were tested (OH and Cl) and the technique was adapted to allow for temperature controlled measurements. Rate coefficients for the reactions of eight VOCs (1,2-, 1,3- and 1,4-diethylbenzene, n-pentylbenzene, 2-methylheptane, 2-methylnonane, ethylcyclohexane and 2,3-dimethylpent-1-ene) with OH at room temperature were derived for the first time. Rate coefficients for the reactions of 44 other VOCs with OH were also assessed concurrently with the derivation of these eight new results. A rate coefficient for the reaction between 2-methylheptane and Cl was measured for the first time, alongside the measurement of rate coefficients for the reactions of seven other VOCs with Cl.