Researchers have discovered that an unknown source is still emitting 39,000 tons of carbon tetrachloride into the atmosphere every year. Such emissions have been banned by the Montreal Protocol for being destructive to the planet’s ozone layer.
The ozone layer is the Earth’s natural defensive barrier against harmful ultraviolet B (UVB) rays emitted by the sun. When allowed to permeate the atmosphere, UVB rays can cause a range of destructive effects to animals, plants and humans. UVB has been shown to inhibit the reproductive cycle of phytoplankton, which form the basis of the ocean’s food chain, as well as fish, shrimp, crabs and amphibians. In humans, excess UVB exposure has been linked to premature skin aging, cataracts, immunodeficiency and nonmelanoma skin cancers, including basal cell carcinoma and squamous cell carcinoma.
Prior to the passage of the Montreal Protocol, emissions of chlorofluorocarbons (CFCs) were slowly breaking down the ozone layer. These chemicals were commonly used in aerosols, refrigerators and air conditioners prior to 1987. When released into the atmosphere, ultraviolet rays break CFCs down into their component substances, which include chlorine. Chlorine reacts with the oxygen atoms in the ozone layer, actually causing it to rip apart. This chemical reaction is what created the “hole” in the Earth’s ozone.
In 1987, countries enacted the Montreal Protocol to stop the use of CFCs in commercial products. In 1996, scientists estimated that it would take about 50 years for chlorine levels in the Earth’s atmosphere to reach their natural balance, but research showed that, overall, the ozone layer was improving.
However, a recent report published in Geophysical Research Letters shows that carbon tetrachloride (CCl4), an ozone-depleting CFC, is still being emitted into the atmosphere. Concentrations of CCl4 in the atmosphere are not consistent with drops in other CFCs, with data showing that emissions are totaling 39,000 tons per year – 30 percent of what CCl4 emissions were before they were banned.
“This very large emissions estimate difference is equivalent to ~1600 railroad tank cars of liquid [carbon tetrachloride],” the researchers write.
As of this writing researchers cannot pinpoint the source(s) of these emissions.