Paul Crutzen received the 1995 Nobel Prize in Chemistry
 

The atmosphere around the earth contains small amounts of the gas ozone. The ozone layer prevents a large part of the dangerous ultraviolet rays from reaching the surface of the earth. Paul Crutzen has made fundamental contributions to our understanding of the formation and decomposition of ozone – processes that are also affected by emission of gases caused by human activity. In particular, he has shown the importance of nitrogen oxides for the ozone balance.

He has also made contribution to knowledge through findings on how the reactions which decompose ozone are considerably reinforced by cloud particles in the stratosphere. That the dilution of the ozone layer is strongest just above the poles of the earth – in particular over Antarctica – is due to this effect. The extremely low temperatures lead to the creation of a very large quantity of cloud particles. Research on the chemical mechanisms in the ozone layer has shown signs of the negative impact of humans. There are now far-reaching international agreements on the prohibition of emission of freons and other gases destroying ozone in the so-called Montreal Protocol.

Paul Crutzen has also studied how ozone is created in the lower stratum of the atmosphere, the troposphere, where the amount of ozone has increased in the last century, due to car exhaust fumes and other emissions. Besides contributing to the greenhouse effect, ozone close to the ground also causes damage to crops and human health.

Paul Crutzen is Dutch and came to the Department of Meteorology, Stockholm University in 1959. He defended his doctoral thesis in 1973 and has continued his activities here during various periods, alongside his work at several large research institutions around the world.

Paul Crutzen shared the 1995 Nobel Prize in Chemistry with Mario Molina and Sherwood Rowland.