Chlorofluorocarbons (CFCs) such as 'Freon' were used in air-conditioning, refrigeration, to generate foam and as propellants in spray cans et cetera. They were, however, banned in the 1990s when they were implicated in the destruction of the protective (reducing the passage of skin-cancer causing UV radiation) ozone layer. Since that time, the CFCs have gradually declined (they are persistent) and the hole in the ozone layer has declined somewhat. Recently scientists have recorded a surprising increase in these agents that they think emanates from East Asia(https://www.theguardian.com/environment/2018/may/16/mysterious-rise-in-banned-ozone-destroying-chemical-shocks-scientists). It is possible, they think, that someone in the region of China, Korea and Mongolia is either making these substances or failing to record them as by-products of another process. It just shows how protection of the environment involves activities over the entire planet (countries can't do it independently).
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