An impact category that still matters
The stratospheric ozone layer absorbs much of the Sun’s incoming ultraviolet UV-B radiation. A reduction in ozone concentration allows more UV-B to reach the Earth's surface, with potential consequences for human health, ecosystems and materials.
Adopted in 1987, the Montreal Protocol established the phase-out of the production and consumption of many ozone-depleting substances. Its implementation has dramatically reduced the use of these substances and put the ozone layer on a recovery path. Recovery is gradual, however: many substances remain in the atmosphere for years or decades, and some controlled uses are still subject to phase-out schedules.
How LCA assesses ozone depletion
In Life Cycle Assessment (LCA), this category considers emissions of substances with ozone-depletion potential throughout a product system, including production, use and end-of-life stages. Historical examples include CFCs and HCFCs, which have been used in refrigeration, air conditioning, foams and certain industrial processes.
Impact-assessment methods characterise these emissions using factors that represent their relative ozone-depletion potential. A common indicator is expressed in kilograms of CFC-11 equivalents. Results depend on the selected method, the substances covered and the quality of the life-cycle inventory.
Do not confuse stratospheric and ground-level ozone
Ozone-layer depletion is not the same issue as the formation of ozone near the ground. Stratospheric ozone protects life from UV-B radiation. Tropospheric ozone is an air pollutant formed through photochemical reactions involving precursors such as nitrogen oxides and volatile organic compounds. In LCA, these are separate impact categories.
Interpreting and reducing results
The choice of refrigerants and blowing agents, leak prevention, proper recovery of equipment and appropriate end-of-life treatment can all affect results. Characterisation factors must match the selected method and version. It should not be assumed that all alternatives to CFCs have the same environmental profile: some replacement substances do not deplete ozone but can have a high global-warming potential.
LCA helps assess these trade-offs across the life cycle rather than focusing on a single property of a substance.