PNNL

Abstract

Assessing future changes in air quality using downscaled climate scenarios is a relatively new application of the dynamical downscaling technique. Because accurately simulating air quality places higher demands on an accurate meteorological simulation than most previous downscaling applications, the ability of regional climate models to adequately generate the requisite variables must be determined. For example, models must generate realistic boundary layer dynamics and the proper frequency of precipitation in addition to precipitation amount and surface temperatures. This article presents two downscaled simulations made using the Fifth-Generation Pennsylvania State University–NCAR Mesoscale Model (MM5). One simulation was driven by the NCEP/NCAR Global Reanalysis product and the other by the Goddard Institute for Space Studies global circulation model. Comparisons of the model runs are made against the ventilation and flow properties of the North American Regional Reanalysis (NARR), and also against observed precipitation. The relative dependence of different simulated quantities on regional forcing, model parameterizations, and large scale circulation provides a framework to understand similarities and differences between model simulations. Based on the comparisons, recommendations are made to improve the utility of downscaled scenarios for air quality assessment.