Alkyl Nitrate Formation from the Reactions of C8-C14 n-Alkanes with OH Radicals in the Presence of NOx: Measured Yields with Essential Corrections for Gas-Wall Partitioning

In this study, C-8-C-14 n-alkanes were reacted with OH radicals in the presence of NO in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of similar to 0.30 at about C-13-C-14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers >= C-3.