As the result of volcanic action resulting in the discharge of gases (especially sulphur dioxide) into the atmosphere, an effect similar to urban smog is created. It can affect people with asthma, allergies and sinus, and can contributes to acid precipitation. Such volcanic smog is also known as vog.
Urban air pollution is increasingly due to road traffic and is a growing environmental problem in many countries. Epidemiological studies have found statistically significant links between air pollution and indicators of both acute and chronic ill health. The resulting annual health costs and loss of wellbeing have surprised many observers: figures of FF 50 000 million (EUR 7600 million) have been put forward for France, while the figure for Switzerland is Sw.fr. 1600 million (EUR 1000 million).
While urban air pollution is coming under control in some countries, the situation is deteriorating rapidly in many heavily industrialized cities in developing countries. In China, for example, smoke and small particles from burning coal cause more than 50 000 premature deaths and 400 000 new cases of chronic bronchitis a year in 11 of its largest cities (World Bank 1997), and private car circulation has been restricted in some cities in South America and Europe in attempts to reduce harmful levels of air pollution. Worldwide, more than 1 000 million urban residents are exposed to health-threatening levels of air pollution (Schwele 1995).