Most pollution doesn’t go above an altitude of around 12 kilometres, where the stratosphere takes over from the troposphere. However, new research by a team led by William Randel, of the National Center for Atmospheric Research in Boulder, Colorado, used satellite readings to show that hydrogen cyanide, a tell-tale ingredient of Asian pollution, was being thrust up by exceptional updrafts of air inside the monsoon’s clouds.

‘The monsoon is one of the most powerful atmospheric circulation systems on the planet, and it happens to form right over a heavily polluted region,’ said Randel. ‘As a result, the monsoon provides a pathway for transporting pollutants up to the stratosphere.’

The research, which has been published in the journal Science, will force atmospheric scientists to rethink the state of the stratosphere. ‘Received wisdom has been that gases such as sulphur dioxide and nitrogen oxides don’t make it into the stratosphere,’ said Peter Bernath of the University of York, who formed part of the research team. Once in the stratosphere, sulphur can form aerosols that influence the ozone layer. The pollution may also alter water vapour and other compounds that affect global climate by influencing the amount of solar radiation that reaches Earth.

June 10