World Ozone Day is a celebration and a reminder that we can do good things when we come together
Spotlight
World Ozone Day is an annual commemoration of the 1987 Montreal Protocol, the global treaty that phased out ozone-depleting chemicals and put the Earth's ozone layer on a path to recovery. This week also marks 60 years of continuous ozone measurements from NOAA's Dobson station in Boulder, Colorado. CIRES sat down with scientist Irina Petropavlovskikh, who has spent her career studying stratospheric ozone, to answer a few simple questions about what it all means. "World Ozone Day is a celebration and a reminder that we can do good things when we come together," Petropavlovskikh said.
The ozone layer is a band of ozone molecules distributed vertically through the stratosphere, high above the Earth's surface, that shields the planet from harmful solar radiation. Without it, that radiation can contribute to eye damage, skin cancers, and reduced agricultural yields. It's distinct from ozone near the ground, which forms as a pollutant and is harmful to breathe rather than protective.
The original culprits were chlorofluorocarbons (CFCs), once widely used in refrigeration and cooling, along with hydrochlorofluorocarbons (HCFCs) that were later used as replacements — both are regulated as ozone-depleting substances under the Montreal Protocol. Those chemicals have largely been replaced by hydrofluorocarbons (HFCs), which don't deplete the ozone layer themselves, but are powerful greenhouse gases. Phasing down HFCs is the focus of the 2016 Kigali Amendment, which this year's World Ozone Day theme specifically celebrates.
Scientists have studied atmospheric ozone since the 1920s and 30s. In 1974, Mario Molina and F. Sherwood Rowland warned that CFCs could destroy the stratospheric ozone layer, but early ground ozone column measurements showed naturally occurring variability without a clear depletion signal. That changed in the 1980s, when observations by Japanese and UK researchers, supported by NOAA instruments in Antarctica, first detected unusual anomalies. Consequently, a team of NOAA and NASA scientists, including Susan Solomon, deployed to Antarctica and helped explain what became known as the Antarctic ozone hole. That discovery led directly to the 1985 Vienna Convention and the 1987 Montreal Protocol.
Scientists have used the Dobson Ozone Spectrophotometer to measure atmospheric ozone concentrations since the 1920s. CIRES scientists work with NOAA's Global Monitoring Laboratory to host the World Dobson Calibration Centre, which calibrates ozone-measuring instruments so that these measurements stay consistent worldwide.
The NOAA Dobson spectrophotometer
The NOAA Dobson spectrophotometer located in Boulder, Colorado has collected continuous ozone measurements for 60 years this week.
The International Ozone Commission (IO3C) has convened ozone scientists globally since the 1930s. Petropavlovskikh joined the commission in 2012, first as a member, then as secretary, and was elected president for a four-year term in 2024. The Commission's signature event is a quadrennial international symposium where scientists share the latest findings, compare notes, and identify open research questions. The last symposium was held in Boulder in 2024 and hosted by CIRES. Findings from these events inform the official World Meteorological Organization/United Nations Environment Programme Ozone Assessment (the next is due later this year). CIRES scientists' recent work on the 2022 Hunga volcanic eruption, which found the eruption caused some localized ozone depletion but only minor effects on the Antarctic ozone hole overall, is a good example of the kind of science that symposium highlights.
Not entirely. The Antarctic ozone hole still forms every year. In fact, we're entering that season now: as sunlight returns to Antarctica, the seasonal ozone hole begins forming again, expanding and contracting each year even as the long-term trend keeps improving thanks to sustained global action. The good news is that the Montreal Protocol and the Kigali Amendment have proven successful and there is a strong international community of scientists who actively collaborate to identify new threats, track progress, and help keep recovery of the ozone layer on course.
Share
CIRES at CU Boulder has partnered with NOAA since 1967
University of Colorado Boulder
© 2026 Regents of the University of Colorado