A review of major chlorofluorocarbons and their halocarbon alternatives in the air

To establish a proper regulation strategy on the emissions of major halocarbons including chlorofluorocarbons (CFCs), carbon tetrachloride (CCl4), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), it is essential to assess their environmental behavior in relation to social and technological changes for their control. The production and release of CFCs and CCl4 increased rapidly to peak between the 1970s and 1980s and then decreased dramatically from the end of the 1980s in good accordance with the phase out schedules set by the Montreal Protocol. Both HCFCs (e.g., HCFC-124, HCFC-141b, and HCFC-142b) and HFCs (e.g., HFC-134a) have been introduced as CFCs alternatives between the late 1980s and early 1990s. However, these alternatives have already been or will be scheduled to be phased out because of their involvement in ozone destruction and global warming. In light of all the complexities associated with the global chemistry of CFCs and their alternatives, this paper provides an overview of their production and emission trends, their relationship with the ozone depletion phenomenon, the chemistry regulating their removal processes, and their distribution patterns with diverse temporal and spatial scales.