Future directions in photochemical air quality modeling

Photochemical air quality models provide the most defensible method for relating future air quality to changes in emission, and hence are the foundation for determining the effectiveness of proposed control strategies. However, strategies, based primarily on controlling reactive organic gas emissions, have not provided the expected benefits. This raises the question of what have been the deficiencies in previous studies utilizing these tools? Furthermore, what changes are necessary, and desired, to improve upon past efforts? The current generation of models have matured within their original frameworks to represent, relatively accurately, the important physical and chemical processes affecting pollutant dynamics in urban atmospheres. The ability to follow regional dynamics is less well demonstrated. Current regional models have a single horizontal resolution scale. Multiscale models will enable detailed treatment of urban chemistry, and also effectively follow long range transport and chemistry. Improved computational capabilities will allow more detailed chemistry and heterogeneous processes to be followed within the models. The practice of photochemical modeling will benefit greatly from recent and future intensive field studies. The advancements in both the model framework and practice will allow much more accurate evaluation of proposed control strategies, and lead to a much improved understanding of pollutant dynamics.