Atmospheric Ozone in Helsinki and Its Effects on Rubber

Although the amount of ozone in the atmosphere is rather small compared with other gases its importance in several respects is rather great. This is mainly due to the high absorption and reacting capacities of ozone. The absorption capacity becomes apparent among other ways in the fact that the ozone layer of the atmosphere absorbs the excessive ultraviolet radiation coming from space as well as heat radiation from the earth. On the other hand, the reacting capacity can best be observed in numerous harmful oxidation phenomena, among which a typical example is the cracking of the surface of rubber products, caused by ozone. Generation and distribution of ozone in the atmosphere.—It is assumed that ozone is generated in the upper atmosphere photochemically under the influence of ultraviolet radiation. The shortwave ultraviolet radiation of a wavelength of about 2000 A breaks the oxygen molecules into atoms that combine with other oxygen molecules to form ozone. The ozone in turn absorbs ultraviolet radiation of a longer wavelength, which again breaks up the ozone thus maintaining an equilibrium in the concentration. This equilibrium is largely dependent upon temperature, the lower temperatures giving rise to a considerably higher concentration of ozone than the higher temperatures. The maximum concentration of ozone in the atmosphere is at an altitude of about 20 kilometers from the earth. The distance of this maximum from the surface of the earth, however, varies over different parts of the globe and according to the season. There is a constant movement of ozone from the actual ozone layer to the lower air regions near the surface of the earth. The major part of the ozone is destroyed near the earth's surface, as it comes into contact with oxidizable matter. Generally speaking, this movement of the ozone into the lower parts of the atmosphere is caused by turbulence, that is, by mixing of the air masses. In the atmosphere there is a regular circulation between the different regions. Near the equator the direction of the movement is upwards, from the troposphere to the stratosphere, while around the latitude 60 it is the other way around. This phenomenon explains, for example, the relatively large increase in radioactivity in polar districts and, in addition, it offers a partial explanation of the high ozone concentration near the surface of the earth in these parts compared with that in warmer regions.