Appauvrissement de l’ozone stratosphérique

• Since the 1980s, observations have revealed significant seasonal reductions in the stratospheric ozone layer above the Arctic and Antarctic continent. These declines can reach 50% at the end of winter and beginning of spring and also affect, though less markedly, mid-latitudes. Ozone layer thinning affects polar regions during spring.

• Research on the subject has shown that ozone layer depletion results from complex chemical reactions occurring in the stratosphere involving brominated or chlorinated compounds requiring very low temperatures, reached during polar winters, followed by significant solar radiation in the following spring. These compounds are emitted by human activities. The most well-known are: • chlorofluorocarbons (CFCs) used in refrigeration systems, air conditioning, aerosol cans, solvents, etc.; • hydrochlorofluorocarbons (HCFCs) developed as replacements for CFCs due to their shorter atmospheric lifespan; • halons used in fire extinguishers and fire protection systems; • carbon tetrachloride used notably as an industrial cleaning solvent; • methyl bromide used for treating plants, facilities and agricultural soils by fumigation.

• Ozone layer depletion, one of nine planetary boundaries (Rockström et al., 2009), is assessed through measurement of stratospheric ozone concentration in Dobson units (DU). Given that the average ozone column value is 300 DU, the boundary is set at 275 DU, namely 95% of its pre-industrial level (290 DU). While this boundary was transgressed in the 1980s, trends have reversed since, and average ozone layer thickness is gradually increasing. In 2009, concentration reached 283 DU. In the 1980s, during the end of the austral winter (September–October), when the sun appears, ozone layer thickness could approach 100 DU.

• To preserve the ozone layer and particularly contribute to its reconstitution, the international community has been committed since 1987 to the Montreal Protocol on Substances that Deplete the Ozone Layer. This international agreement aims to progressively halt the production and consumption of the substances involved. 197 countries have signed this protocol. Since its entry into force, global emissions of these products have fallen by over 80% and virtually all chemical products controlled by the Protocol have been eliminated. • At the same time, according to the World Meteorological Organization, observations of the layer show that in certain parts of the stratosphere, the ozone layer has recovered at a rate of 1 to 3% per decade since 2000. According to projections, the ozone layer above the northern hemisphere and mid-latitudes should fully recover by 2030, the ozone layer above the southern hemisphere in the 2050s, and that above polar regions by 2100.

• France ratified the Montreal Protocol in 1987. However, it continues to produce and consume substances covered by the Protocol. Indeed, in the absence of available alternatives, the Protocol provides exemptions to authorize the use of certain regulated substances for specific uses such as use as a manufacturing agent, as a synthesis intermediate, or for laboratory uses. Finally, some of these substances are introduced to the national market before being destroyed in facilities treating hazardous waste. • CFCs: None: None: 210 • Halons: 408: None: 5 • Carbon tetrachloride: 13,207: 9: 3,166 • 1,1,1-trichloroethane: 21,652: None: None • HCFCs: 35,349: None: 135

• In 2016, refrigerant fluid emissions in metropolitan France approached 8,000 tonnes.

• Support measures are being implemented to help businesses implement alternative actions to eliminate ozone-depleting substances for certain processes (refrigerant fluid for example). Thus hydrofluorocarbons (HFCs), second-generation substitutes for CFCs and then HCFCs, are the subject of heavy use. However, HFCs are greenhouse gases with high global warming potential. Over the period 1990–2016, their emissions increased by 324% in metropolitan France.

• The Kigali Amendment, signed in 2016 and entered into force on 1 January 2019, aims to reduce the production and consumption of chemical products releasing powerful greenhouse gases into the atmosphere and used in refrigerators, air conditioners and related devices. This text, which frames and establishes reduction schedules for HFC production and consumption for all Parties to the Protocol, was ratified by France on 29 March 2018. France has committed to reducing its HFC consumption and production by 85% by 2036 (compared to the reference years 2011–2013). • This article is an excerpt from the synthesis report of the 2019 edition of the report on the environment in France.