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Sole: All concentrations are expressed in /ig m 3 as sulfur. Percentage values give the area of the region considered relative to the total area of Europe

Sole: All concentrations are expressed in /ig m 3 as sulfur. Percentage values give the area of the region considered relative to the total area of Europe

The vertical profile of S02 concentration was first studied in the troposphere by Georgii and Jost (1964). Their mean results obtained over the F.R.G. are plotted in Fig. 14. It is seen that the S02 concentration decreases rapidly with increasing altitude under continental conditions. At a height of about 1000 m the concentration drops to half its value in the surface air. Above 2 km the annual variation disappears and above 3 km the concentration decrease becomes insignificant. This constant concentration is approximately 5 fig m~3 STP. However, more recent aircraft flights (e.g. Rodhe, 1972a; Trag&rdh, 1978; Varhelyi, 1978) resulted in a smaller concentration at this height. Varhelyi (1978), for example, found the corresponding figure over Hungary to be about one order of magnitude smaller than the concentration proposed by Georgii and Jost (1964). In contrast, the results of aircraft flights, carried out by Gravenhorst (1975) over the Bay of Biscay, indicate much less S02 vertical decrease over the sea than over continental areas.

An interesting peculiarity of the vertical sulfate profile is the small value of the concentration gradient compared to the S02 concentration decrease (Georgii, 1970; Varhelyi, 1978). It follows from this fact that the S0^"/S02 ratio increases with increasing height. This is due, in part to the gradual conversion of S02 to sulfate particles in updrafts as well as to the difference in deposition velocity of gases and particles (see later). The observations of Varhelyi (1978) lead to sulfate concentrations around 1 fig m~3 at an altitude of 3 km, which is about twice the corresponding S02 level (see above).

Concerning sulfate concentration in surface air, the level of this species has no maximum in the winter (Bonis, 1968), in contrast to the annual variations of S02. That is, high winter S02 concentrations do not necessarily coincide with a high sulfate content of particulate matter. This phenomenon can be explained by the interaction of different conversion processes (E. Meszaros, 1974b) of sulfur gases. According to the observations of Kolb (1973), carried out in a very clean environment (Tromso, N. Norway), the annual variation of S04 ~ shows a spring maximum and a minimum during the fall like the tropospheric 03 concentration (see Fig. 13). However, more numerous American studies indicate a summer maximum in the annual distribution of sulfate level (Hidy et at. 1978).

Another interesting feature of sulfate concentration is the increase above the tropopause. Thus, in the stratosphere around 16 and 18 km a sulfate layer can be found, the formation and characteristic of which will be discussed elsewhere (Subsection 4.4.3).

On the basis of his data compilation, including the results of some aircraft flights, E. Meszaros (1978) estimates values for atmospheric S02—S and S04—S burden as shown in Table 14. The figures proposed by Friend (1973) are also given for comparison. All values are expressed in sulfur equivalents. The agreement between the two authors on S02—S burden is excellent. However, more atmospheric sulfate-sulfur mass was calculated by E. Meszaros. Thus, Meszaros' estimates show a greater sulfate-sulfur burden than that of S02—S. It is to be noted that stratospheric S04—S is not included in sulfate burden. However, the total quantity of sulfate-sulfur in the stratosphere (Karol, 1977) is at least one order of magnitude less than the global mass in the troposphere.

Tabic 14

Global atmospheric sulfur burden over the oceans and continents according to Friend (1973) and E. Meszaros (1978)

Friend

Mèszirtx

Friend

Mészàros

Oceans

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