| Summary: | Climate changes and atmospheric pollution are currently topical issues given their possible dramatic effects from the health, social and economical points of view. Assessing the causes and possible adaptation/mitigation strategies is a challenge in modern science. To understand and quantify the anthropic role in such changes is of a particular interest to depict future scenarios and to warn politicians about local and global intervention in emissions control. Ozone is one of the most important trace gases in the Earth's atmosphere. It is mainly present in the stratosphere, with only 10% in the troposphere. Despite its small amount, (2-7) 10ô 3 % in molar fraction, the solar radiation at wavelengths below 310 nm does not reach the Earth surface because of the large absorption cross sections characterizing ozone molecules at those wavelengths. Variations in the stratospheric ozone content may play a dramatic role in a possible increase of the surface UV radiation. The discovery of the Antarctic ozone hole, i.e. a considerable reduction of ozone in the polar stratosphere, was a dramatic evidence of the effects of anthropogenic emissions on the ozone layer. Human activity is likely responsible also for tropospheric ozone enhancements caused by the photochemistry associated to industrial emissions involving ozone precursors as the nitrogen dioxide. The effect of these variations at lower altitudes, with respect to background values, have been estimated to be the third largest source of the greenhouse effect. To support interpretation of the atmospheric phenomena, as well as interactions with the oceans and the ground, a constant and systematic monitoring of several atmospheric parameters, and with a good spatial coverage, is crucial. In this framework, global and systematic space-based observations of the atmospheric composition and its variations in time and space play a major role. Satellite measurements of atmospheric parameters has a proven and recognized effectiveness for such tasks. The advantage of atmospheric ...
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