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Abstract

A quantitative understanding of long-range transport of air pollution involves several aspects from different science areas: emissions of ozone precursors, greenhouse gases, aerosols and aerosol precursors must be known not only in their amount, but also with regard to their geographic distributions and seasonal variations, wind fields must be available in sufficiently high spatial and temporal resolution, vertical transport processes such as convection or frontal lifting must be captured, and the chemical transformations of pollutants must be considered. Three-dimensional numerical models of atmospheric chemistry and transport provide a means to address all of these issues simultaneously. In this chapter we discuss the state-of-the-art of such models and present a summary view of a number of issues related to long-range transport (i.e. transport pathways, regional and global impact of various source regions) as it emerges from numerical simulations of the atmosphere. We focus on tropospheric ozone, because it illustrates the interactions between transport and chemistry, and it is also of immediate relevance for air quality regulations. Global models have contributed significantly to the understanding of the long-range transport of ozone and its precursors, but there is still considerable uncertainty with respect to important terms of the ozone budget. This makes quantitative predictions of the impact of long-range transported air pollution difficult. We discuss the shortcomings of todayrsquos models and provide an outlook into future developments.