Effects of an Ether Group on the Mechanism, Products, and Nitrate and Secondary Organic Aerosol Yields for the Reaction of Dioctyl Ether with OH/NOx
Anna Ziola, John Orlando, PAUL ZIEMANN, University of Colorado Boulder
Abstract Number: 266
Working Group: Chemicals of Emerging Concern in Indoor and Outdoor Aerosol: Sources, Vectors, Reactivity, and Impacts
Abstract
Ethers are a particularly interesting class of VOC whose atmospheric chemistry is still not fully understood. They are common components of volatile chemical products, reformulated “cleaner” gasoline, solvents used by industry, and agricultural products, and have been shown to react much faster with OH radicals and have lower organic nitrate and SOA yields than the corresponding alkanes. For example, in a study of C5 and C6 ethers it was shown that an ether group reduced the organic nitrate yields by ~50% compared to the corresponding alkane, while others have shown that the SOA yields from C5–C10 glycol ethers (which typically contained two ether and one hydroxyl groups) were <1%. In the light of these results, we have conducted an environmental chamber study of the effect of an ether group and a long alkyl chain on the branching ratios between organic nitrate and alkoxy radical formation, the reaction products and mechanism, and SOA yield using dioctyl ether [CH3(CH2)7O(CH2)7CH3] (DOE) as a model compound. The presence of an ether group and symmetric structure greatly simplifies the reaction products and mechanism compared to glycol ethers, which have multiple ether and hydroxyl groups, each of which impacts H abstraction by OH radicals, organic nitrate and alkoxy radical formation, and alkoxy radical decomposition and isomerization throughout the molecule. This complexity makes it difficult to interpret product measurements and determine the impact of an ether group. In addition, the two C8 alkyl chains in DOE allow alkoxy radicals to isomerize faster away from the ether group than with short alkyl chains, thus potentially competing with decomposition since isomerization across the ether group is slower by a factor of ~30 due to ring strain. All these factors make for an easier comparison to the reactions of large alkanes, which we have studied in detail.