Sensitivity Analysis of Urban Photochemical Smog by Using a Reduced Version of an Air Quality Model

Abstract

A reduced version of a comprehensive urban-scale photochemistry model has recently been developed in order to make it possible the inclusion of urban-scale processes as sub-grid scale phenomena in global-scale models (Calbo et al., 1998). More specifically, this re-duced model is presently being linked to the MIT Integrated Global System Model for Cli-mate Policy Assessment (Prinn et al., 1998). The reduced model is in fact a parameterization consisting of a set of analytical expressions that approximate the predictions by the CIT Ur-ban Airshed Model as functions of fourteen input parameters. For each species, effective emissions are a function of actual urban emissions of this and other species and of other properties such as meteorology. The probabilistic collocation method was applied to develop the parameterization. This method uses the probability density functions of the inputs to generate a set of orthogonal polynomials. These polynomials are then used as the basis for a polynomial expansion that approximates the actual response of the CIT model to its inputs. Seasonal variation is assumed to be represented by sinusoidal functions. Since the param-eterization provides a computationally very efficient simulation of the actual model behavior, it is applicable to uncertainty and sensitivity analysis of the urban pollution physics and pho-tochemistry.