Why study globalscale environmental chemistry

In previous chapters of this book the chemistry of the atmosphere, oceans and land has been dealt with largely on an individual basis. Using a steady-state model (see Section 3.3), we can envisage each of these environments as a reservoir. In each chapter the cycling of chemicals has been discussed, together with their transformations within the reservoir. Where relevant, some attention has been paid to inputs and outputs into or out of that reservoir from or to adjacent ones. By contrast, the present chapter focuses not on individual reservoirs, but on the ensemble of them that make up an integrated system, of air, water and solids, constituting the near-surface environments of our planet.

As scientists have learnt more about the way chemical constituents of the Earth's surface operate, it has become clear that it is insufficient to consider only individual environmental reservoirs. These reservoirs do not exist in isolation — there are large and continuous flows of chemicals between them. Furthermore, the outflow of material from one reservoir may have little effect on it, but can have a very large impact on the receiving reservoir. For example, the natural flow of reduced sulphur gas from the oceans to the atmosphere has essentially no impact on the chemistry of seawater, and yet has a major role in the acid-base chemistry of the atmosphere, as well as affecting the amount of cloud cover (Section 7.3).

Since integrated systems need to be understood in a holistic way, studies of the global environmental system and natural and human-induced changes to it have become very important. By definition, such studies are on a large scale, generally beyond the resources of most nations, let alone individual scientists. Thus, in recent years several large international programmes have been put in place, the most relevant to environmental chemistry being the International Geosphere-Biosphere Programme (IGBP) (further information can be found at http://www.igbp.kva.se) of the International Council for Science. This has as its aim:

To describe and understand the interactive physical, chemical and biological processes that regulate the total Earth system, the unique environment that it provides for life, the changes that are occurring in this system, and the manner in which they are influenced by human actions.

This large research agenda is concerned not only with understanding how Earth systems currently operate, but also how they did in the past as well as predicting how they may change in the future as a result of human activities and other factors.

This chapter examines the global cycling of carbon, sulphur and persistent organic pollutants (POPs) at or near the Earth's surface. These examples, concerned with natural or human-induced alterations to new or existing cycles (see Section 1.4), have been selected because they are chemicals that circulate widely in the atmosphere, with potential impacts on large regions of, if not the whole, planet.

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