Many particles reflect solar radiation back into space which may lead to a local cooling of the atmosphere. Others, however, behave in the opposite way, absorbing light and warming the atmosphere.

The nature of the Swiss terrain means that atmospheric inversion sometimes occurs, normally in winter. Cold air is trapped beneath a layer of warmer air, and air pollution in the lower layer cannot escape. This is a vicious circle: the pollutants themselves help prevent an exchange of air.

Smog is sometimes a feature of the Swiss summer. Under the influence of sunlight nitrogen oxide and hydrocarbons (or volatile organic compounds) in the air cause ozone to form, which is a danger to health and to the environment.

The research station on the Jungfraujoch is being used by an international team of scientists to conduct research into the behaviour of these particles. They are interested not only in their interaction with light, but also in their chemical composition and the way in which they influence cloud formation.