Prediction of Rate Constants for Gas-Phase Reactions of Nitrate Radical with Organic Compounds: A New Structure-Activity Relationship

A new structure-activity relationship (SAR), based on parametrization of the molecular structure according to the group-additivity method, is presented. On the basis of existing experimental data for the degradability of approximately 150 organic compounds by the NO3 radical, this new SAR is developed to estimate the rate constants for reactions with NO3 radical. At night, nitrate radicals are the most important oxidant of volatile organic compounds. The rate constants for their reactions are therefore essential to the understanding of VOC degradation and atmospheric modelling. The database used for the SAR development includes most classes of compounds such as alkanes, alkenes (acyclic and cyclic), dienes, terpenes and saturated and unsaturated oxygenated compounds (including alcohols, ketones, ethers and esters). The proposed SAR shows good efficiency, as 91% of the rate constants are reproduced within a factor of two. The overall agreement between measured and predicted rate constants is very good for most of the unsaturated and saturated compounds, although for saturated alcohols it is less reliable.