The transport sector as a source of air pollution

Transport first became a significant source of air pollution after the prob lems of sooty smog from coal combustion had largely been solved in western European and North American cities. Since then, emissions from road, air, r ail and water transport have been partly responsible for acid deposition, s tratospheric ozone depletion and climate change. Most recently, road traffi c exhaust emissions have been the cause of much concern about the effects o f urban air quality on human health and tropospheric ozone production. This article considers the variety of transport impacts on the atmospheric envi ronment by reviewing three examples: urban road traffic and human health, a ircraft emissions and global atmospheric change, and the contribution of su lphur emissions from ships to acid deposition. Each example has associated with it a different level of uncertainty, such that a variety of policy res ponses to the problems are appropriate, from adaptation through precautiona ry emissions abatement to cost-benefit analysis and optimised abatement. Th ere is some evidence that the current concern for road transport contributi on to urban air pollution is justified, but aircraft emissions should also give cause for concern given that air traffic is projected to continue to i ncrease. Emissions from road traffic are being reduced substantially by the introduction of technology especially three-way catalysts and also, most r ecently, by local traffic reduction measures especially in western European cities. In developing countries and Eastern Europe, however, there remains the possibility of great increase in car ownership and use, and it remains to be seen whether these countries will adopt measures now to prevent tran sport-related air pollution problems becoming severe later in the 21st Cent ury. (C) 2001 Elsevier Science Ltd. All rights reserved.