Anthropogenic chemicals, stratospheric

In recent years a great deal of scientific attention and public concern has been directed at the problem of ozone depletion in the Earth s stratosphere caused by anthropogenic chemicals. Ozone is toxic, and... 

Before we discuss the chemistry of the stratosphere in detail, let us first briefly consider how chemicals emitted at the earth s surface are transported into the stratosphere and, conversely, how stratospheric species are transported into the troposphere. This issue is important as it determines which species end up in the stratosphere as we shall see, it is only those that survive for a sufficiently long time in the troposphere that are transported into the stratosphere. Thus, reactive organics (larger than CH4) from the troposphere do not survive to reach the stratosphere in appreciable quantities. Similarly, transport from the stratosphere to the troposphere is the major mechanism for removal of the products of the reactions of anthropogenic species that occur in the upper atmosphere. In addition, some 03 is injected into the troposphere, which is a natural source upon which anthropogenic production of 03 is imposed (see Chapter 16). 

Halogens are very reactive chemicals that are known to play an important role in anthropogenic stratospheric ozone depletion chemistry, first... 

In this book air chemistry is defined as a branch of atmospheric science dealing with the atmospheric part of the biogeochemical cycle of different constituents. In other words this means that we will deal mainly with the atmospheric pathways of those components that are involved in the mass flow between the atmosphere and biosphere, as well as in chemical interactions between the air and the other media of our environment (soils, oceans etc.). It follows from this definition that, on the one hand, our discussion will be restricted to the troposphere and the stratosphere4 and, on the other hand, the photochemistry of the upper layers, the subject matter of the aeronomy (e.g. Nicolet, 1964), will be omitted. This separation of the (photo) chemistry of the lower (troposphere and stratosphere) and upper atmosphere makes it possible to give a more compact treatment of our problem, including the global anthropogenic effects due to the increase of air pollution. 

The bathtub analogy uses the level of water in the tub to illustrate the ozone concentration in the stratosphere. Naturally occurring reactions in the atmosphere produce and consume ozone at equal rates to maintain a steady-state concentration, just as the rate of water added to a bathtub could be adjusted to exactly match the rate of water draining from the tub and maintain a constant level in the tub. Additional chemical reactions of anthropogenic origin that consume ozone would correspond to the addition of extra drains to the tub so that the level of water in the tub would drop. 

N2O has recently received much attention because it greatly contributes to the greenhouse effect and leads to a severe damage of the ozone layer in the stratosphere. Generally, N2O can be produced by both natural and anthropogenic sources. In comparison with the natural sources, N2O emissions, which should be decreased in the short period, are related to the chemical and energy industries. The major N2O emission of chemical production results from adipic acid and nitric acid plants (Ertl, Knozinger, Schuth, Weitkamp, 2008). 

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