Fifty years ago the famous London Smogs occurred throughout the city to which the United Kingdom now has pleasure in welcoming the 13th World Clean Air and Environmental Protection Congress. They were to prove a landmark in environmental policy, and since then advances in science and policy have transformed the environment not only of London but of many other cities around the world.

While this is a cause for optimism all of us know that enormous challenges remain, and new ones have emerged. In many areas of the world air pollution still exacts a heavy toll in human life and environmental degradation, and to atmospheric pollution has been added the enormous challenge of climate change and the many other environmental and social problems which still inhibit sustainable development.

These problems remain urgent, and it is also clear that they now require concerted international action, not only among political leaders but also among scientists, regulators, business people and the ordinary citizens in local communities.