Many old fridges contain chemicals called Chlorofluorocarbons (CFCs) which damage the Earth's ozone layer.

BBC: Ghana bans second-hand fridges

Nitrous oxide is also considered a greenhouse gas and is 310 times more dangerous to the Earth's ozone layer than carbon dioxide, said Joseph Johns, chief of the U.S. attorney's environmental crimes section.

NPR: Feds Raid 17 Calif. Businesses For Nitrous Oxide

The ozone layer protects living things on the Earth's surface from the Sun's ultra-violet radiation.

BBC: Ill wind 'killed dinosaurs'

During the dinosaurs' time on Earth, "the atmosphere became charged with methane, which finally damaged the ozone layer and brought about great changes in the vegetation, " it added.

BBC: Ill wind 'killed dinosaurs'

While the ozone layer in the upper atmosphere plays an important role in limiting harmful ultraviolet light reaching the Earth's surface, low-level ozone is a pollutant that is harmful, causing respiratory problems in animals as well as well-documented cases in humans.

BBC: Invasive plant 'increases ozone pollution'