Chemistry and Pollution of the Stratosphere

Abstract

This chapter deals with perhaps the most iconic symbol of global atmospheric pollution – the ‘ozone hole’. Discovered in the mid-1980s, the ‘hole’ is a dramatic reduction in ozone amounts above the Antarctic in southern springtime that continues to appear each year. Similar losses occasionally occur above the Arctic in northern springtime, for example in spring 2011. These springtime ozone losses, at heights of 12–25 km, are the result of a subtle interplay between gas-phase chemistry, reactions on aerosol particles, and global-scale atmospheric circulation. The gas-phase chemistry controlling stratospheric ozone involves radical oxides of hydrogen, nitrogen, chlorine and bromine in catalytic cycles so that, even when the radicals are a thousand-fold less abundant than ozone, the radicals can effect large changes in ozone abundance. The aerosol particles in the stratosphere usually come from volcanic eruptions (and other smaller sources) but there is discussion now of putting aerosol particles into the stratosphere, as a geoengineering scheme, to reduce global warming deliberately. This injection of artificial aerosol particles could have negative consequences for the evolution of the ozone layer if it was to be implemented. Although there are many natural sources of the gases that produce radical oxides, anthropogenic emissions of chlorine-, bromine- and nitrogen-containing gases have added greatly to the potential for stratospheric ozone destruction. The most important of these gases, the chlorofluorocarbons and their relatives, have been very successfully regulated through the Montreal Protocol and its amendments. In the coming century, nitrous oxide, from fertiliser use, may become the most important anthropogenic ozone-depleting substance.