Which of the following chemical materials is responsible for the depletion of the ozone layer in the atmosphere?
(1) Nitrous oxide
(2) Carbon dioxide
(3) Chlorofluorocarbon
(4) Sulphur dioxide
Answer: (3) Chlorofluorocarbons (CFCs) and other halogenated ozone-depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion. CFCs were invented by Thomas Midgley, Jr. in the 1920s. They were used in air conditioning and cooling units, as aerosol spray propellants prior to the 1970s, and in the cleaning processes of delicate electronic equipment. They also occur as byproducts of some chemical processes. No significant natural sources have ever been identified for these compounds; their presence in the atmosphere is due almost entirely to human manufacture.