At a Glance

Researchers say the ozone layer is thinning over areas with dense populations. The sun shines brighter in these areas, leaving people more vulnerable to UV rays. Scientists are unsure what is causing the ozone layer to remain depleted over these spots.

Parts of the ozone layer have been bouncing back, but researchers have found that the barrier isn’t improving over more populated areas, making people more vulnerable to the sun’s UV rays.

Despite showing improvement over the Antarctic, in the Earth’s lower stratosphere, according to a recent study. The stratosphere is the atmospheric layer that sits roughly 6 to 31 miles above the troposphere, the lowest layer where all of our weather happens. The lower portion of the stratosphere is home to a big chunk of the ozone layerand it soaks up large amounts of UV rays.

“The study is in lower- to mid-latitudes, where the sunshine is more intense, so ,” study co-author and Grantham Institute for Climate Change and the Environment at Imperial College London co-director Joanna Haigh told The Guardian. “It is a worry.”

Scientists are unsure what is causing the ozone layer to falter at lower latitudes, but some have suggested that harmful chemicals may play a role.

In 1987, officials agreed upon the Montreal Protocol, which phased out chemicals called chlorofluorocarbons (CFCs), according to the release. This led to the first signs of recovery at lower latitudes in the layer’s upper stratosphere.

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“Ozone has been seriouslydeclining 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,” Haigh said in the release. “The potential for harm in lower latitudes may actually be worse than at the poles. The decreases in ozone are less than we saw at the poles before the Montreal Protocol was enacted, but UV radiation is more intense in these regions and more people live there.”

In addition to the CFCs, previous research showed levels of dicholoromethane, a “very short-lived substance” (VSLS) found in paint remover and aerosols, have , The Guardian reports. The chemical is not currently banned and researchers don’t know much about where it’s being emitted from and why the levels have gone up so quickly.

“The finding of declining low-latitude ozone is surprising since our current best atmospheric circulation models do not predict this effect,” ETH Zurich university professor and study lead author William Ball said in the release. “Very short-lived substances could be the missing factor in these models.”

Scientists previously believedVSLSs did not stick around long enough to rise into the atmosphere and impact the ozone layer, but further study into this may be required.

Researchers have also suggested that global warming is causing the circulation of the atmosphere to change and push more of the ozone away from the tropics, according to the release.

For the study, the scientists used atmospheric ozone measurements from 11 different sets of data to create a record spanning across the last 30 years. It accounts for levels in the ozone between an area ranging from Russia, Alaska and Scandinavia to South America’s tip, according to The Guardian.

The scientists say their studies should now be focused on obtaining more exact data about the decline of the ozone in order to figure out what the likely cause is.