Variations in the chemical composition of stratosphere

The aim of this section is to discuss the modifications of the atmospheric composition which can be related to the variations of the radiation balance and temperature observed in this century. We shall first deal with the relation between short-range modifications of atmospheric (stratospheric and tropospheric) composition and the transfer of incoming radiation. After this discussion, atmospheric factors influencing the absorption of infrared radiation emitted by the Earth s surface will be presented briefly. 

From the foregoing parts of this book it is clear that solar radiation in the stratosphere is primarily attenuated by ozone (see Subsection 3.4.3) and at a lesser extent by the stratospheric sulfate aerosol layer (see Subsection 4.4.3). This means that any change in the stratospheric 03 burden or aerosol concentration involves modification of radiative transfer in this atmospheric domain. We should remember that the residence time of trace constituents above the tropopause is rather long because of the thermal structure and the absence of wet removal. Furthermore at these altitudes the density of the air is low as compared to that of lower layers. For this reason even an insignificant quantity of pollutants can produce relatively long and significant effects. 

The study of the possible modification of the stratospheric ozone shield seems to be particularly important since ozone absorbs radiation dangerous to living species. Furthermore, this substance plays an important role in the control of the heat balance of the stratosphere. 

One possible agent of inadvertent stratospheric modification is NO, emitted by supersonic transport aircraft. As discussed in Subsection 3.4.3 NO, takes part in photochemical processes in the stratosphere in such a way that it catalyzes the reaction of O and 03 molecules (see also Fig. 9). That this reaction occurs was confirmed in individual cases by measuring the vertical profile of 03 over an area (Berlin) where supersonic transport is heavy (Grasnick, 1974). It is much more difficult, however, to assess long-range global effects. One estimate (Rowland, 1976) states that if 100 supersonic aircraft of models available at present were operated, the increase in ultra-violet radiation erythermally effective would be 0.04 % at the 

Calculated effects of fluorocarbons on global ozone according to Wofsy el al. (1975). A production held constant at present rate B production ceases in 1978 C production increases by 10 per year, ceases in 1995 D production increases by 10 per year production increases by 22 % per year, ceases in 1987 F production increases by 22 per year. (Copyright 6.2.1979 by the American Association for the 

---