Despite some recent good news about the ozone recovery, a new study suggests that ozone levels in densely populated low latitudes do not seem to be recovering as they do in the polar regions. Although there is no clear explanation, the problem is due to ozone-destroying chemicals, such as those found in paint removers and degreasers.

The ozone layer ACTS as a protective barrier to protect humans and animals from harmful ultraviolet radiation. In the 1970s, chlorofluorocarbons, used in refrigerators and aerosols, were found to be the main cause of stratospheric ozone depletion and were eventually phased out in 1987 under the Montreal protocol on ozone-depleting substances.

Cutting-edge research shows, however, even though over the Antarctic ozone hole is gradually repair, but in 60 ° and 60 ° N S latitude within the scope of the hole in the ozone layer do not show signs of recovery. These latitudes range from Russia to densely populated areas around Australia.

Dr Joanna Haigh, co-author of the study and co-director of the grantham research institute at imperial college London, said: "the potential harm from lower latitudes may actually be more serious than the polar regions. Before the Montreal protocol was enacted, there was less ozone reduction than we saw at the poles, but ultraviolet radiation was stronger in those areas, and there were more people living there."

Using new algorithms and data from various satellite missions conducted since 1985, the team created a long time series that revealed longer-term trends in lower altitude and higher ozone reduction in the stratosphere between 10 and 50 kilometers (6.2 to 31 miles). Although they have not yet been able to provide any definitive explanation, the researchers have come up with some theories.

One theory is that a shift in atmospheric circulation patterns caused by climate change could take more ozone away from the tropics. Another theory is that material that can only exist briefly in the atmosphere (VSLSs) is thought to stay in the atmosphere for not long enough to reach the stratosphere and affect the ozone layer, which could take longer than expected.

William Ball, from the federal institute of technology in Zurich, said: "the finding of a lower latitude fall in ozone is surprising because our current better atmospheric circulation patterns do not predict this effect. The transient presence of matter in the atmosphere may be the missing factor in these models."

The team's paper has been published in the European geophysical union's journal atmospheric chemistry and physics.