Ozone shift studied
The ozone layer above Antarctica is mending, but ozone levels are actually dropping in the lower stratosphere.
Atmospheric chemists are struggling to find a culprit for the ozone-draining, though new studies suggest global warming is likely playing a role.
Overall, the total amount of ozone in the entire atmosphere has remained steady, because ozone levels in the troposphere — the lower part of the atmosphere in which we live — are rising.
It is not good news.
Ozone should not be so close to the Earth’s surface, and its increase has been linked to air pollution.
Burning fossil fuels produces nitrogen oxides, which go on to produce ozone.
Ozone is very effective at destroying plants, and damages human lungs.
In the 1970s, it was recognised that chemicals called CFCs, used in refrigeration and aerosols, were destroying ozone in the stratosphere. The effect was worst in the Antarctic, where an ozone ‘hole’ formed.
In 1987, the Montreal Protocol was agreed, which led to the phase-out of CFCs and, recently, the first signs of recovery of the Antarctic ozone layer. The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.
Ozone has been declining globally since the 1980s, but while the banning of CFCs is leading to a recovery at the poles, the same does not appear to be true for the lower latitudes.
The cause of this decline could be man-made climate change, but there are a couple of other possibilities.
One is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere.
VSLSs include chemicals used as solvents, paint strippers, and as degreasing agents. One is even used in the production of an ozone-friendly replacement for CFCs.
The latest analysis has used new algorithms to combine the efforts of multiple international teams that have worked to connect data from different satellite missions since 1985 and create a robust, long time series.