Preliminary Results from Regional Modeling of the KIE, in the Oxidation of Hydrocarbons

The modeling of the reactions with the OH-radical of stable isotopes of Non Methane Hydrocarbons (NMHC) can help to understand important pollution sources. Modeling the stable isotope ratio (δ 13C) also can be used to study the contribution of air pollution transport. The effect of isotopes on a rate constant is referred to as a kinetic isotope effect (KIE). The OH radical will tend to abstract the most weakly bound hydrogen atom in the molecule. So in NMHC reactions with OH the overall rate constant reflects the number of available hydrogen atoms and the strengths of C-H bonds, therefore the effect of one 13C atom in a molecule of NMHC will change the rate constant. The rate constants of NMH13C reactions with the OH-radical were determined from recent and on going laboratory measurements of KIE (Proffessor Rudolph's Group York University). The model used for this study was the MC2AQ model. The model includes on-line gas phase chemistry, and covers part of Eastern US and Canada on a 21km grid scale. The model was modified to include isotope information for Propene, Toluene, Propane, Benzene, Xylenes, and Isoprene. These compounds (both ¹²C and 13C were included as tracers reacting only with OH, with no feedback on the main chemistry in the model. This will help to test and verify the OH-radical concentration predicted by the chemistry model. The changes in (δ ¹³C) of less reactive (or more reactive) NMHC due to the mixing of air masses is studied from the output of the model.