The ozone layer is damaged primarily by synthetic chemicals containing chlorine and bromine, which rise into the upper atmosphere and break apart ozone molecules. Since the 1980s, a global treaty has eliminated 99% of the worst offenders, but several threats remain, including agricultural emissions, unregulated industrial solvents, and a growing space launch industry.
How Ozone Gets Destroyed
Ozone molecules sit in the stratosphere, roughly 15 to 35 kilometers above Earth’s surface, where they absorb most of the sun’s ultraviolet radiation. When certain gases reach this altitude, they release chlorine or bromine atoms that tear ozone apart in a chain reaction. A single chlorine atom doesn’t get used up in the process. It acts as a catalyst, cycling through reactions that convert ozone into ordinary oxygen over and over again. One chlorine atom can destroy thousands of ozone molecules before it’s finally removed from the stratosphere.
Over the poles, especially Antarctica, the destruction is even more efficient. Extremely cold temperatures create ice clouds in the stratosphere, and chemical reactions on the surface of those cloud particles release huge amounts of reactive chlorine all at once. When sunlight returns in spring, that chlorine goes to work, and ozone levels plummet. This is what creates the “ozone hole” that forms over Antarctica each year.
The Chemicals That Caused the Most Damage
Chlorofluorocarbons, better known as CFCs, are the single biggest reason the ozone layer thinned in the late 20th century. They were used in refrigerators, air conditioners, aerosol spray cans, foam packaging, and insulation. CFCs are extremely stable at ground level, which is exactly why they’re so dangerous: they survive long enough to drift into the stratosphere, where ultraviolet light finally breaks them apart and frees their chlorine atoms.
Other major ozone-depleting chemicals include:
- Halons: Used in fire extinguishers, these release bromine, which is even more destructive to ozone per atom than chlorine.
- Carbon tetrachloride: Once widely used as an industrial solvent and in the production of CFCs themselves.
- HCFCs: Introduced as a transitional replacement for CFCs. They’re less harmful but still carry chlorine into the stratosphere.
The 1987 Montreal Protocol phased out production of these substances worldwide. Implementation has eliminated 99% of ozone-depleting chemical emissions, roughly 1.8 million tonnes in ozone-damage terms. It’s widely considered the most successful international environmental agreement ever enacted.
The Biggest Current Threat: Agricultural Emissions
By 2008, nitrous oxide had become the largest ozone-destroying gas still being emitted by human activity. It comes mainly from microbial activity in fertilized soil, with smaller contributions from livestock waste, industrial processes, and fossil fuel combustion. Unlike CFCs, nitrous oxide is not regulated under the Montreal Protocol.
This matters more now than it used to. With CFC emissions nearly eliminated, nitrous oxide’s relative importance keeps growing. Reducing it would do more to protect the ozone layer than controlling any of the remaining unregulated industrial chemicals, either individually or combined. The catch is that meaningful reductions would require significant changes in agricultural practices, particularly in how fertilizers are applied, and that’s far harder to regulate than banning a factory chemical.
Unregulated Industrial Solvents
A class of chemicals called very short-lived substances has quietly been offsetting some of the progress made under the Montreal Protocol. These are industrial solvents, primarily dichloromethane, along with chloroform, perchloroethylene, and 1,2-dichloroethane. They break down within six months at the surface, which is why regulators originally assumed they’d never reach the stratosphere. That assumption turned out to be wrong.
Dichloromethane is the biggest concern. Its concentration in the lower atmosphere roughly doubled between the early 2000s and the mid-2010s, driven largely by industrial use in East Asia. The total chlorine these short-lived chemicals deliver to the stratosphere grew from about 69 parts per trillion in 2000 to 111 parts per trillion in 2017. Their share of total stratospheric chlorine rose from around 2% to 3.4% over the same period. That growth has partially offset the chlorine reductions achieved by phasing out CFCs.
Rocket Launches
The rapid growth of the space industry introduces ozone-depleting pollution directly into the stratosphere, bypassing the long atmospheric journey that ground-level emissions have to make. Solid rocket fuels release chlorine gas and alumina particles. Alumina is particularly problematic because it accelerates chlorine-driven ozone destruction by an order of magnitude more than an equal mass of naturally occurring sulfate particles in the stratosphere.
Rockets burning kerosene or other carbon-based fuels deposit black carbon soot at high altitude. Even water vapor from rocket exhaust can contribute to ozone loss by encouraging the formation of polar stratospheric clouds, the same ice clouds that accelerate the Antarctic ozone hole. Re-entering debris and reusable rocket components add nitrogen oxides from the intense heat of atmospheric re-entry. The total impact is still small compared to legacy CFC damage, but with launch rates climbing sharply, this is a source worth watching.
Natural Factors: Volcanoes and Solar Cycles
Volcanic eruptions and changes in the sun’s energy output both affect ozone levels, but neither one explains the long-term depletion observed since the 1980s. Large eruptions like El Chichón in 1982 and Mount Pinatubo in 1991 injected sulfur gases into the stratosphere, creating particles that sped up chlorine-driven ozone destruction for a few years afterward. Once the volcanic particles settled out, the extra depletion stopped.
Solar cycles cause ozone levels to fluctuate by 1 to 2% between the sun’s peak and low activity periods, on a roughly 11-year cycle. But solar output over recent decades shows no downward trend that could account for the roughly 4% average ozone depletion measured from pre-1980 levels. In short, natural forces create temporary wobbles in ozone, while synthetic chemicals cause the sustained damage.
Old Appliances Still in Use
Even though CFC production has stopped, older refrigerators, freezers, window air conditioning units, and dehumidifiers manufactured before the mid-1990s may still contain CFCs in their refrigerant lines and insulation foam. When these appliances are improperly discarded, crushed in a landfill, or left to corrode, those chemicals escape into the atmosphere. If you’re disposing of an old appliance, the refrigerant needs to be professionally recovered before the unit is scrapped. Most municipal waste programs and appliance retailers handle this.
Where Recovery Stands
The ozone layer is healing, but slowly. According to the most recent scientific assessment, ozone is expected to return to 1980 levels (before the hole appeared) by around 2040 for most of the world, 2045 over the Arctic, and 2066 over Antarctica. The 2025 Antarctic ozone hole was notably small and short-lived, consistent with the long-term recovery trend.
The timeline depends on continued compliance with the Montreal Protocol and on whether newer threats, particularly nitrous oxide and short-lived industrial solvents, are brought under control. HFCs, the chemicals that replaced CFCs in most cooling systems, don’t destroy ozone directly, but they’ve been found to slow the recovery slightly. Full recovery within this century remains the expectation, but it isn’t guaranteed if new emission sources grow unchecked.