Country to country transport of anthropogenic sulphur in Southeast Asia

The MATCH model—driven by archived meteorological data from the ECMWF—has been used to study the long-range transport of pollutants in Southeast Asia during the year 2000. We have specifically investigated the atmospheric export and import of anthropogenic sulphur between nine countries in Southeast Asia as well as the import to these countries from the boundaries of our model domain, from southern China, and from international shipping in the surrounding waters.Compared to the conditions at the mid-latitudes (Europe, North America and East Asia), we find less long-range transport in this part of the world. In all countries in the region (except those with very small area, i.e. Singapore and Brunei), did the major part of the domestic emissions (60–70%) fall down on the emitting country itself. The fraction of the countries own emissions contributing to the total, annually accumulated, national deposition varied from 10% for Laos—which is a country with small emissions neighbouring large emitters—to 80–90% in countries not surrounded by significant emitters (i.e. Thailand, Indonesia, Singapore and Brunei).Sensitivity tests were performed to explore the uncertainties in the model simulations and to investigate to what extent the current results could be used for source–receptor relationships in the future, when the magnitude and location of the emissions may be different. We found that the general feature—with relatively little long-range transport of sulphur—will not be altered, while the absolute magnitude of the deposition in areas downwind of large emitters could change considerably if certain model parameters, or the emission patterns are changed. This is particularly true in light of the seasonal variation of the deposition pathways. The atmospheric import of anthropogenic sulphur from specific countries can vary by an order of magnitude between different months. Incidentally, a decrease in import from one country during a certain period is often compensated by a roughly equal increase of the import from another country during the same time.