Least independent variables method for simulation of tropospheric ozone

Abstract

We describe a method for simulating photochemical production of O in a continental‐scale tropospheric model with only six independent chemical variables representing tracers transported in the model. The tracers are two primary hydrocarbon families, CO, NO, peroxyacylnitrates, and odd oxygen (O). A chemical module is developed to compute the production and loss rates of tracers over a model time step of 4 hours, using only information on the tracer concentrations input to the module at the beginning of the time step. Test simulations for summertime conditions at mid‐latitudes indicate little loss in accuracy compared to detailed model simulations of chemistry with high time resolution. Minimization of the number of tracers and use of a long time step reduces computer time and storage requirements. In addition, parameterization of the chemical computation is facilitated, allowing further savings in computer time.