When I first started writing about the HVACR industry more than 25 years ago, the term used to describe the harmful effects of refrigerant emissions in the atmosphere was ODP. After scientists discovered the hole in the ozone layer, they determined that it was caused by the chlorine in chemical compounds like CFCs, which were widely used in aerosols and refrigerants. They needed a measurement to describe the amount of ozone depletion caused by various substances, thus the term ODP was born.