Ozone Depletion Potential Calculator

Ozone depletion potential is a relative index, not an absolute quantity. It is defined as the integrated global loss of stratospheric ozone caused by a unit mass emission of a compound, divided by the loss caused by the same mass of CFC-11 (trichlorofluoromethane), which is fixed at 1.0 by convention. Multiplying an emission by its ODP therefore converts it into CFC-11 equivalent kilograms, the currency in which Montreal Protocol production and consumption caps are written. Three physical factors set a compound ODP: how many chlorine or bromine atoms it carries, what fraction of the molecule survives tropospheric removal long enough to reach the stratosphere, and how efficiently the released halogen runs the catalytic cycle before being locked up as HCl or ClONO2. Bromine is roughly 45 to 60 times more destructive per atom than chlorine, which is why Halon-1301 is assigned about 10 and Halon-1211 about 3, against 0.055 for HCFC-22 and 0.11 for HCFC-141b. HFCs and HFOs are zero because they contain no chlorine or bromine. Two cautions matter. ODP-weighted emissions do not translate linearly into Dobson units of column ozone loss, because depletion depends on polar stratospheric cloud chemistry, transport and the total halogen burden already present; any single-emission ozone-loss figure is an order-of-magnitude illustration only. And ODP says nothing about climate: HFC-134a has zero ODP but a 100-year GWP near 1,430, which is why a separate CO2-equivalent calculation is needed alongside it.

The chemistry underlying ODP was established in stages. Paul Crutzen showed in 1970 that catalytic nitrogen oxide cycles could destroy stratospheric ozone, and in 1974 Mario Molina and F. Sherwood Rowland published in Nature the argument that inert chlorofluorocarbons would drift into the stratosphere, be photolysed by ultraviolet light and release chlorine atoms capable of destroying many thousands of ozone molecules each. The three shared the 1995 Nobel Prize in Chemistry. The ODP index itself was introduced in the early 1980s, notably in work by Donald Wuebbles around 1983, as a way of ranking candidate replacement compounds using one dimensionless number derived from two-dimensional atmospheric chemistry models. Urgency arrived in 1985 when Joseph Farman, Brian Gardiner and Jonathan Shanklin of the British Antarctic Survey reported in Nature that springtime ozone over Halley Bay had fallen dramatically since the late 1970s, a loss measured in Dobson units, the column unit named after the Oxford physicist G. M. B. Dobson. The Vienna Convention was agreed in 1985 and the Montreal Protocol was signed in 1987, entering force in 1989, with ODP thresholds used to sort substances into control annexes and phase-out schedules. Later amendments tightened those schedules, and the 2016 Kigali Amendment extended the treaty to high-GWP HFCs that have no ozone impact at all. WMO and UNEP scientific assessments, published roughly every four years, remain the source for the ODP values in regulatory use.