Earth’s ozone layer has been depleting since the 1970s due to certain man-made chemicals. After the ban on the harmful chemicals, parts of the ozone layer is showing recovery.

A new study has shown that ozone layer’s bottom part at more populated latitudes is not healing. Scientists still do not know the exact reason why there is no recovery in these parts.

The Ozone Layer

During the 1970s, scientists had understood that the chemicals known as CFCs such as aerosols and those used in refrigeration were detrimental to the ozone layer. The ozone layer above Antarctica had taken the worst hit and an ozone hole had formed.

An international treaty called the Montreal Protocol was signed in 1987 at the Vienna Convention to protect the ozone layer by supervising the production of the harmful substances that led to its depletion. Following the phase-out of CFCs, the Antarctic ozone layer showed the first symptoms of healing.

However, though the upper stratosphere at lower latitudes is also showing positive signs of healing, which proves the effectiveness of the Montreal Protocol, the ozone layer in the lower stratosphere is gradually disintegrating. The ozone layer is present in the stratosphere at an altitude of about 10 to 50 kilometers.

"In tropical and middle latitudes" -- home to most of humanity -- "the ozone layer has not started to recover yet," said William Ball, the lead author of the study and a researcher at Zurich’s Swiss Federal Institute of Technology in Zurich. "It is, in fact, slightly worse today than 20 years ago."

The new research, which was based on the measurements of multiple satellites, estimated that it has now depleted an added 0.5 percent. If the measurements are confirmed, it would indicate that the ozone depletion level is at right now at its highest level. Furthermore, the possibility of harm in the lower latitudes may be worse than that seen at the poles.

New Study Findings

The study concluded that the worrying trend could have two probable suspects. It could be caused by chemicals that are known as very short-lived substances, used in decreasing agents, paint strippers, and solvents, which attack the lower stratosphere ozone layer. For example, in the past decade the use of one such VSLS, dichloromethane has doubled.

The Montreal Protocol does not cover regulations on the use of VSLS, whose effect persists for six to 12 months. According to Ball, if VSLS is identified as the problem then those chemicals can be banned too, and it would be relatively easier to deal with.

The problem arises if global warming is the culprit leading to the ozone layer’s renewed breakdown. Climate change could be altering the pattern of atmospheric circulation, carrying away the ozone from the tropics.

"If climate change is the cause, it's a much more serious problem," Ball added. "We should be concerned but not alarmed."

The study was published in the journal Atmospheric Chemistry and Physics on Feb. 6.