The ozone layer, which has been recovering slowly since the Montreal Protocol (1987) banned CFC gases, is again threatened, this time by a chemical compound used in paint strippers, warns a study Tuesday . Levels of methylene chloride (or dichloromethane), a compound not affected by the Montreal ban, are rapidly increasing in the stratosphere, threatening to delay the return to normal of the ozone layer, alerts the study published in Nature Communications. Although “modest at present, the impact of dichloromethane on ozone has grown significantly in recent years,” writes the team of American and British researchers. “Continued growth would offset some of the gains made by the Montreal Protocol,” they add. The ozone layer forms a gaseous shield, between 10 and 50 km altitude, protecting the Earth from ultraviolet rays. In 1987, an international agreement was signed to gradually eliminate CFC gases (used in refrigeration and aerosols), responsible for the famous “hole” in this gaseous layer. CFCs have thus been replaced by HFCs (which, however, help to warm the planet). Scientists have already expressed concerns about the impact of certain volatile compounds, such as dichloromethane. The new study attempts to evaluate the damage caused by this product, used as a solvent for paints and varnishes, industrial degreaser and … for decaffeinating coffee. According to this research, the level of dichloromethane in the stratosphere has almost doubled since 2004. If this growth were to continue, it could delay the recovery of ozone over Antarctica by more than a decade – where the “hole” was most alarming. “We must act now to stop the emanations of dichloromethane into the atmosphere if we want to avoid ruining 30 years of exemplary scientific and political action that has undoubtedly saved many lives,” said Grant Allen, an atmospheric physicist at the University of Manchester, in a commentary. In any case, this study shows that protecting the ozone layer “is a much bigger industrial and political challenge than we expected,” said David Rowley of University College London.