Gas-phase chemical mechanism compression strategies: Treatment of reactants

A new technique for condensing detailed organic reactions into more compact forms is introduced, and compared to methods which have been used in the ADOM and RADM air quality models. The previous methods made use of integrated reactivity weighting, designed to predict the correct product concentrations on time scales of one to two days or longer. The latter methods are shown to be subject to high errors in the prediction of initial hydrocarbon product concentrations. These errors occur when the hydrocarbon chemistry is the most reactive. The new method is a hybrid scheme which uses the reaction rates at the initial time as a further constraint on the lumping. This results in improved prediction of product concentrations on shorter time scales while retaining the long-term accuracy of the earlier techniques. The hybrid reactivity weighting technique is shown to have higher accuracy than the earlier ADOM or RADM techniques in the regions of the most reactive chemistry, and is therefore very relevant to regional oxidant models.