Abstract
Abstract. Reaction with the hydroxyl (OH) radical is the dominant removal process for volatile organic compounds (VOCs) in the atmosphere. Rate coefficients for reactions of OH with VOCs are therefore essential parameters for chemical mechanisms used in chemistry transport models, and are required more generally for impact assessments involving the estimation of atmospheric lifetimes or oxidation rates for VOCs. Updated and extended structure–activity relationship (SAR) methods are presented for the reactions of OH with aliphatic organic compounds, with the reactions of aromatic organic compounds considered in a companion paper. The methods are optimized using a preferred set of data including reactions of OH with 489 aliphatic hydrocarbons and oxygenated organic compounds. In each case, the rate coefficient is defined in terms of a summation of partial rate coefficients for H abstraction or OH addition at each relevant site in the given organic compound, so that the attack distribution is defined. The information can therefore guide the representation of the OH reactions in the next generation of explicit detailed chemical mechanisms. Rules governing the representation of the subsequent reactions of the product radicals under tropospheric conditions are also summarized, specifically their reactions with O2 and competing processes.
Highlights
It is well documented that volatile organic compounds (VOCs) are emitted into the atmosphere in substantial quantities from both anthropogenic and biogenic sources (e.g. Guenther et al, 2012; Huang et al, 2017)
In the present paper, updated structure–activity relationship (SAR) methods are presented for the reactions of OH with aliphatic organic compounds, with the reactions of aromatic organic compounds considered in a companion paper (Jenkin et al, 2018a)
The performance of the method is significantly improved by defining a set of rate coefficients for H-atom abstraction from formyl groups in RC(=O)H, for a variety of different classes of R
Summary
It is well documented that volatile organic compounds (VOCs) are emitted into the atmosphere in substantial quantities from both anthropogenic and biogenic sources (e.g. Guenther et al, 2012; Huang et al, 2017). Aumont et al, 2005), for which it is impractical to carry out experimental kinetics studies This has resulted in the development of estimation methods for OH rate coefficients (e.g. see Calvert et al, 2015; and references therein), which have been applied widely in chemical mechanisms and impact assessments. The information is currently being used to guide the representation of the OH-initiation reactions in the generation of explicit detailed chemical mechanisms, based on the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A; Aumont et al, 2005), and the Master Chemical Mechanism (MCM; Saunders et al, 2003). The treatment of the subsequent chemistry (e.g. reactions of peroxy radicals) will be reported elsewhere (e.g. Jenkin et al, 2018b)
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