Abstract
Trends in air pollutant emissions from 1970 to the present day are described and discussed for the United Kingdom and the United States. These are compared with trends in ambient concentrations and the similarities and divergences are discussed. There have been notable success stories in terms of reductions in smoke and sulfur dioxide concentrations, although the current concentrations are still a matter of concern. Concentrations of carbon monoxide and many volatile organic compounds have decreased very substantially in recent years. Nitrogen dioxide, particulate matter and ozone still give cause for concern. The trends in the United Kingdom and United States are contrasted with those in less developed countries for which China is taken as a case study. The trends in emissions and airborne concentrations are reviewed and contrasted with those in the more developed world.