Meteorology of long-range transport

The increasing attention to regional-scale transport of pollution has resulted in numerous air quality networks, models and large scale field studies to relate the sources of pollution to subsequent air quality measurements and thence to the effects of pollution. We compare observed air quality and trajectory data to calculations to quantitatively evaluate the differences. Methods of preparing air trajectories are described with emphasis on the Air Resources Laboratories' trajectory model and an accompanying diffusion model. The comparison of observed atmospheric transport with calculated trajectories shows that large computational errors can occur and more importantly that these may be systematic, but different, depending on the type of advection (cold vs warm) and whether the transport is over land or over the sea. We describe the use of tetroon recovery locations in trajectory analysis and show that such data can be obtained over distances up to 4000 km. Computed trajectories based on the geostrophic assumption and on the observed wind field are compared to observations to determine the adjustments required to obtain the best comparisons. Directional adjustments of up to 40° and changes in speed by a factor of two are sometimes necessary. We make suggestions for studies to improve the capability of calculating trajectories, including experiments using balloons and controlled tracer releases. Both of these techniques are applicable over regional scales. Finally we show the global distribution of sulfur from the industrial areas of the Northern Hemisphere, as calculated by an efficient computer model, as a step in the determination of the global sulfur budget.