The emergence of numerical air quality forecasting models and their application

In recent years the U.S. and other nations have begun programs for short-term local through regional air quality forecasting based upon numerical three-dimensional air quality grid models. These numerical air quality forecast (NAQF) models and systems have been developed and tested over the last thirty years through retrospective applications for air quality management. Air quality forecasting is a newer application area and brings with it significant new challenges. Such systems are now in operational or experimental use in the U.S., Canada, Europe, Australia, among other locations, and are operated by government, private sector, and academic organizations. We present several examples of such systems now in operation within North America, including the NOAA National Weather Service Eta-CMAQ system, Baron Advanced Meteorological Systems MM5-MAQSIP system, Environment Canada GEM-CHRONOS system, and the NCAR/NOAA WRF-Chem system. The forecast systems are briefly described, including a discussion of particular challenges encountered during development or application, and example forecasts are provided. Results from a recent air quality forecast model intercomparison are shown based on applications during the 2004 ICARTT (International Consortium for Atmospheric Research on Transport and Transformation) field study focused on the northeast U.S. The concept of “ensemble” air quality model forecasts is illustrated as part of the model intercomparion study. Future challenges for NAQF are also discussed, including chemical data assimilation in modeling systems, integrated meteorological/chemical systems, and interactions with global models for specifying boundary conditions.