AIR POLLUTION AND THE CHEMISTRY OF OUR TROPOSPHERE

In the mesosphere, from 50 to 85 km, the temperature again falls with altitude and vertical mixing within the region occurs. This temperature trend is due to the decrease in the CL concentration with altitude. At about 85 km the temperature starts to rise again because of increased absorption of solar radiation of wavelengths 200 nm by 02 and N2 as well as by atomic species. This region is known as the thermosphere. 

The transition zones between the various regions of the atmosphere are known as the tropopause, stratopause, and mesopause, respectively. Their locations, of course, are not fixed, but vary with latitude, season, and year. Thus Fig. 1.1 represents an average profile for mid-latitudes. Specific temperatures, pressures, densities, winds, and the concentrations of some atmospheric constituents as a function of altitude, geographic position, and time are incorporated into a NASA model, the Global. Reference Atmosphere Model (GRAM) information on obtaining this model and data is included in Appendix IV. 

We shall see throughout this book that different chemical and physical processes occur in the troposphere and stratosphere, and we shall frequently refer to different regions in Fig. 1.1. However, it is important to put the atmosphere in perspective with respect to the size of the earth itself. The earth s average diameter is 12,742 km, yet the average distance from the earth s surface to the top of the stratosphere is only 50 km, less than 0.4% of the earth s diameter The space shuttle orbits outside the atmosphere, but at an altitude of only several hundred miles, which is less than the distance from Los Angeles to San Francisco. Clearly, the atmosphere is a very thin, and as we shall see, fragile shield upon which life as we know it on earth depends. 

Concern over air pollution has been well documented (Brimblecombe, 1978). The impacts of atmospheric chemistry on human health and the environment can be traced back many centuries, indeed some two thousand years. For example, the Mishnah Laws in Israel in the first and second centuries A.D. required that, because of the odors emitted, tanneries be located at least 30 m away from the town and only on the east side, due to prevailing westerly winds (Mamane, 1987). 

In the twelfth century, the Hebrew philosopher, scientist, and jurist Moses Maimonides (1135-1204) wrote (Goodhill, 1971) 

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