OH radical initiation reactions

Rates of initial reactions

Rate coefficients for the reactions of OH with organic compounds have been reviewed extensively by Atkinson (1989; 1994; 1997a), Atkinson et al. (1999) and Calvert et al. (2000), with recommendations made in a large number of cases. These recommendations are used unless superseded by more recent evaluations. If recent laboratory determinations are available, which are likely to influence, or form the basis of future recommendations, these are also taken into account. Where no experimental data exist, rate coefficients appropriate to 298 K are estimated by a number of reported methods. For alkanes, carbonyls and chlorinated hydrocarbons, the structure-activity relationship (SAR) method devised by Atkinson (1987), and subsequently updated by Kwok and Atkinson (1995) and Atkinson (2000b), is employed.

The SAR method of Peeters et al. (1994) is used for alkenes and dienes, and the group reactivity (GR) method developed by Dagaut et al. (1989), and updated by Porter et al. (1997), is used for alcohols, glycols, ethers and glycol ethers, as described previously by Jenkin and Hayman (1999).

Initial radical products

Where the relative importance of product channels for reaction of OH with a given VOC has been determined by laboratory investigation, the data are used accordingly. This information is generally available in the kinetics evaluations. In the majority of cases, such data are not available, however, and the initial distribution of radical products is estimated from partial rate coefficients calculated using the SAR and GR methods referred to above. In some cases, the chemistry is simplified by limiting the number of product channels, as described in detail in the previous protocol (Jenkin et al., 1997).