In the past, much of the development for the simulation of different Earth system components such as weather and air chemistry has occurred independently. As a result, most atmospheric predictive models treat chemistry and meteorology decoupled from each other. Yet accurate forecasting of air quality and aerial transport of hazardous materials may depend strongly on interactions of chemistry and meteorology. This chapter describes state-of-the-art approaches that couple these two and allow feedback at each model timestep, both from meteorology to chemistry and from chemistry to meteorology. Dispersion forecasts and global climate change are described as two archetypal examples of coupled weather–chemistry systems.

Introduction

Many of the current environmental challenges in weather, climate, and air quality involve strongly coupled systems. It is well accepted that weather is of decisive importance for air quality or for the aerial transport of hazardous materials. It is also recognized that chemical species will influence the weather by changing the atmospheric radiation budget and through cloud formation. However, a fundamental assumption in traditional air quality modeling procedures is that it is possible to make accurate air quality forecasts (and simulations) even while ignoring much of the coupling between meteorological and chemical processes. This commonly used approach is termed “offline”. Here, we describe a modeling system―and some relevant applications―that represents an opportunity to include these coupled interactions.