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-60" -40° -20° 0° 20° 40° Figure 1.1. Measured ozone and temperature profiles over Thalwil, Switzerland, 1%7.

which, next to water vapor, is the most important gas for the photochemistry of the atmosphere. Without ozone, the chemistry and chemical composition of the atmosphere would be totally different.

Looking at the temperature and ozone profiles of the atmosphere, as shown in Figure LI, we recognize that in the troposphere - that part of the atmosphere where temperatures decrease with height - ozone concentrations are quite low; Higher up, in the stratosphere, ozone concentrations rise steeply with altitude until 25-30 km, and temperatures no longer decrease. Because of this even temperature distribution with height, vertical mixing in the stratosphere is much suppressed. This is also why the stratosphere is characterized by quiet "weather," There are also few clouds in the stratosphere; however, the exceptions are important.

The stratospheric temperature structure is directly connected to the ozone distribution. The ozone that accumulates in the stable layer of the stratosphere absorbs upwelling "warm11 infrared radiation from the Earth's surface as well as ultraviolet (UV) radiation from the Sun. The latter is the same process that largely protects life on Earth from this potentially harmful radiation. This absorption of radiation from above and below provides an important energy source for the stratosphere and explains why temperatures do not decrease with height. Ozone concentrations and temperatures in the stratosphere are very closely coupled. Stable meteorological conditions keep most ozone in the stratosphere, limiting the flow of this poisonous gas to the Earth's surface and largely confining the hydrological cycle to the troposphere. The strong coupling of ozone and temperature in the stratosphere is in my opinion a very important property of the atmosphere that is insufficiently recognized by the climate research community.

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200 r

Processes

Ionization

Dissociation Processes

02 + hv —20 (X % 240 nm) O + O2 + M —O3 + M (2x)

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