Aerosol Junge layer

Carbonyl sulfide is also the most abundant reduced sulfur gas in Earth s troposphere, but for completely different reasons. Volcanic sources of OCS are negligible by comparison with biogenic emissions, which are important sources of several reduced sulfur gases (e.g., OCS, H2S, (CH3)2S, (CH3)2S2, and CH3SH) in the terrestrial troposphere. Many of these gases are ultimately converted into sulfate aerosols in the troposphere, but OCS is mainly lost by transport into the stratosphere, where it is photochemically oxidized to SO2 and then to sulfuric acid aerosols, which form the Junge layer at —20 km in Earth s stratosphere. 

Carbonyl sulfide COS is emitted from terrestrial soil, ocean and biomass burning into the atmosphere, but since their loss rate in the troposphere is very small, most of them reach to the stratosphere. The photolysis of COS in the stratosphere is a very crucial reaction as it provides sulfur into the atmosphere forming sulfuric aerosol layer (the Junge Layer) in the stratosphere. Incidentally, although COS is often described as OCS in the textbooks and literature of atmospheric chemistry, the notation of COS is used in this book according to the recommendation of lUPAC (International Union of Pure and Applied Chemistry). 

Determining the size distribution and composition of the stratospheric aerosols and their evolution have been among the main questions posed since the discovery of the layer (Junge et d., 1960). The steady state... 

The results of the experiment (Chen and Lelevkin, 2000) show, that before the Pinatubo volcano eruption, in the background period the area of 24-29 km was marked out with local minimmns in the correlation function at which the main mass of flie background aerosol was concentrated. This happened at the height of the maximum ozone concentration (24-27 km), not in the field of the Junge aerosol layer, so one can expect that the ozone accumulation takes place there, i.e. 6)3 is generated from the photooxidation of SO2 by air oxygen (Ivlev et. al., 1990) S02 C ) + 2 0( P). 

At the end of the fifties a program was started in the U.S. A. to study stratospheric aerosol particles. The results of the program were analyzed by Junge and his associates (see Junge, 1963). The most important achievement of this study was the discovery of an aerosol layer between 15-20 km consisting mostly of large particles (see Subsection 4.3.3). 

The dry deposition of aerosol particles (D ) is generally measured by horizontal microscopic slide or so-called dustfall cans and jars. However, the results of such measurements, wide-spread in local pollution studies (Corn, 1976), have to be interpreted with caution because of the disturbance of the laminar and turbulent flow regime by the collector. Furthermore, the laminar layer covering the collector surface may be very different from that over soil and vegetation. In any case, if we also measure the particle concentration N, a parameter with the dimension of velocity can be defined (Junge, 1963) ... 

Yet another problem that recently has been brought closer to a solution is the origin of the stratospheric aerosol layer discovered by Junge et al. (1961). The layer centers at altitudes near 20 km and consists mainly of particles representing a mixture of sulfuric acid and water. A number of... 

Schemes that one may apply to deduce aerosol residence times from various radioactive elements have been reviewed by Junge (1963), Martell and Moore (1974), and Turekian et al. (1977). The published data admit residence times in the range 4-72 days, but crowd into two groups of values averaging 6 and 35 days, respectively. From the evidence available to him, Junge (1963) concluded that the higher value was appropriate to the troposphere as a whole and that the lower values were applicable only to the boundary layer near the Earth surface. Martell and Moore (1974), after having critically reviewed older and newer data, came to the opposite conclusion, namely, that the high values are due to the contribution of stratospheric aerosols, apart from misinterpretations of some data, while the lower values represent the true tropospheric residence time essentially independent of altitude.

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