Volcanoes have massive impacts on the stratospheric load of these tiny sulphate particles.

BBC: More sulphur trails from the stratosphere

Ozone-destroying reactions happen faster on surfaces, such as those provided by sulphate particles, than they do in the open air.

ECONOMIST: Geoengineering

Chemical reactions on the volcanic sulphate particles blasted into the stratosphere by the eruption accelerated ozone depletion over the southern hemisphere by about 3%.

BBC: News | Sci/Tech | Ozone hole reaches record size

Sulphate particles, meanwhile, survive only a few years in the atmosphere.

ECONOMIST: Geo-engineering

Another issue is that a second type of pollutant, aerosols such as the minute sulphate particles that form when sulphurous fuel is burned, promote the formation of clouds.

ECONOMIST: Changing science

Injecting sulphate particles into the stratosphere, for instance, would cool the Earth by reflecting more sunlight into space. (Nature has already shown that this concept can work, since volcanic eruptions that send sulphur-rich plumes into the stratosphere can temporarily alter the world's climate.) However, Dr Lenton notes that the method becomes less effective as the atmosphere becomes more saturated with particles.

ECONOMIST: Geo-engineering