1839 Discovery of the ozone by C.F. Schönbein
1860 Surface ozone started to be measured at hundreds of locations
1880 Strong absorption band of solar radiation between 200 and 320 nm attributed to upper atmosphere ozone by Hartley
1913 Proof from UV measurements that most ozone is located in the stratosphere
1920 First quantitative measurements of the total ozone content
1926 Six Dobson ozone spectrophotometers are distributed around the world for regular total ozone column measurements
1929 The Umkehr method for vertical ozone distribution is discovered and determines the ozone maximum is lower than 25 km
1930 Photochemical theory of stratospheric ozone formation and destruction based on chemistry of pure oxygen
1934 Ozone sonde on balloon shows maximum concentration at about 20 km
1955 Global network of ozone stations proposed for IGY
1957 WMO assumes responsibility for standard procedures for uniform ozone observations and the Global Ozone Observing System (G030S) established
1965 Photochemical theory of ozone with destruction by HOx radicals
1966 First ozone measurements from satellites
1971 Ozone destruction by NOx mechanism proposed
1974 Start of consideration of ClOx chemistry as an ozone-destroying mechanism
1974 Human-produced CFCs recognized as source of stratospheric chlorine
1975 WMO conducts first international assessment of the state of global ozone
1977 Plan of Action on Ozone Layer established by UNEP in collaboration with WMO
1981-94 Scientific assessments of the state of the ozone layer issued in 1981, 1985, 1988, 1991 and 1994 by WMO in collaboration with UNEP and national research agencies
1984 Unusually low (~200 m atm cm) total ozone at Syowa, Antarctica, in October 1982, first reported at the Ozone Commission Symposium in Halkidiki, but its significance was recognized only the next year
1985 Vienna Convention for the Protection of the Ozone Layer concluded and data from Halley station on the existence of an ozone hole during Antarctic springs since the early 1980s published by the British Antarctic Survey
1986 Analysis of Montsouris (Paris) surface ozone ( 1873-1910) indicates levels then were less than half of the present
1987 Montreal Protocol on Substances that Deplete the Ozone Layer concluded under UNEP auspices and basic assessment of the State of the ozone initiated by the International Ozone Trends Panel
1988 Decrease of ozone concentrations by ~10% per decade in the lower stratosphere documented; proof from NASA Antarctic Campaign that active chlorine. and bromine byproducts of human activities are the cause of the Antarctic -spring ozone hole
1990 London amendment to strengthen the Montreal Protocol by phasing out all CFC production and consumption by 2000
1991 The WMO/UNEP Ozone Assessment - 1991 reveals ozone is declining not only in winter-spring but all year round and everywhere except over the tropics; very large. concentrations of ClO measured in the Arctic confirms concerns for potential stronger ozone decline
1992 Copenhagen amendment further strengthened Montreal Protocol by phasing out CFCs by the end of 1995, adding controls on other compounds
1992-94 Extremely low ozone values (~ 100 m atm cm) during Antarctic spring and largest area ~24 m. km2 covered; also the lowest ever ozone values measured during the northern winter- spring seasons all indicating increasing destructive capability by increasing chlorine and bromine concentrations in the stratosphere
1995 Record low ozone values (exceeding 25% below long-term average) observed January to March over Siberia and a large part of Europe

A joint publication of the World Meteorological Organization and the United Nations
Environment Programme on the occasion of the fiftieth anniversary of the United Nations


World Meteorological Organization
and United Nations Environment Programme