Introduction

The atmosphere is in the news! Atmospheric chemistry has become a matter of public concern in the last two decades. While the complexities of modern science do not usually spark off great political and social debate, the changes in the atmosphere have evoked great interest. Heads of state have been forced to meetings in Stockholm, Montreal, Kyoto and Johannesburg and given their attention to the fate of our atmosphere. Television, which normally relegates scientific matters to off-peak hours, has shown skilfully created colourful images from remotely sensed measurements of the ozone (O3) hole and huge emissions from forest fires of 1997 that have continued to raise concern into the current century. What has caused this interest in the atmosphere?

The atmosphere is the smallest of the Earth's geological reservoirs (Fig. 3.1). It is this limited size that makes the atmosphere potentially so vulnerable to contamination. Even the addition of a small amount of material can lead to significant changes in the way the atmosphere behaves.

We should note that the mixing time of the atmosphere is very rapid. Debris from a large accident, such as the one at the nuclear reactor at Chernobyl in 1986, can quickly be detected all over the globe. Pollutant particles from Europe and North America can be detected over China. This mixing, while distributing contaminants widely, dilutes them at the same time. By contrast, the spread of contaminants in the ocean is much slower and in the other reservoirs of the Earth takes place only over geological timescales of millions of years.

Fig. 3.1 Relative sizes of the major reservoirs of the Earth. Units, 1024g.
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