Aerosol particles scatter and absorb solar radiation affecting visibility as well as the Earth's radiative balance (the so-called "direct effect"). In addition, particulate matter can serve as cloud condensation nuclei (CCN), thereby influencing the albedo (first indirect effect), lifetime and amount of clouds. Despite several decades of observational study, the current understanding of aerosol effects on weather, both with respect to their direct radiative impact and the effects of aerosol on clouds, is not complete. Numerical forecast models serve an important in the study of aerosols as they permit the separate study of each effect as well as allow scientists to consider future studies and scenarios.

One numerical model that is being developed and evaluated for such study is the Weather Research and Forecast model (WRF) with chemistry (Grell et al., 2004). The WRF-Chem model is designed to integrate the meteorology and atmospheric chemistry simultaneously. The WRF-Chem model incorporates several air chemistry mechanism and aerosol packages with biogenic emissions, surface deposition, convective transport, turbulence, photolysis, and advective transport. In addition, aerosol interaction with shortwave radiation (Fast et al. 2006) has been included.

Preliminary results from a case study using the WRF-Chem model will be presented. The presentation will focus upon evaluating the “direct” radiative effects, and its interaction with the atmosphere This is a detailed study of a full physics run for one day only during the New England Air Quality (2004) field experiment. Even though the indirect effect is not simulated, there is fairly large effect on cloud and temperature fields when comparing runs with and without the radiative feedback. We will explore and discuss the differences in the simulation results.