Evaluation of New Trace Gas and Aerosol Modules in WRF-chem using Measurements from TexAQS

1.0 INTRODUCTION Much progress has been made in modeling trace gases such as ozone and ozone precursors; however, relatively large uncertainties are still associated with urban, regional, and global-scale model predictions of aerosols (mass, size distribution, composition, physical characteristics, and optical properties) and aerosol direct and indirect forcing. A key step in improving the representation of particulates in global climate models is to first improve the performance of urban to regional scale models that can resolve many of the sub-grid scale processes a global climate model cannot. We have used the PNNL Eulerian Gas Phase and Aerosol Scalable Unified System, PEGASUS (Fast et al., 2002), over the past several years to investigate how local to regional-scale meteorological processes influence the evolution of oxidants and particulates. However, PEGASUS employs “off-line” coupling of meteorology with chemistry and aerosols so that feedback mechanisms cannot be simulated. In anticipation of the emerging scientific issues associated with the interaction of mega-city pollutant emissions, regional air-quality, and climate change, we have begun using the Weather Research and Forecasting (WRF) community model as a framework to develop, evaluate, and improve aerosol parameterizations. In this study, we describe our on-going model development activities as well as preliminary results of coupled meteorologychemistry-aerosol predictions for an urban area.