Vertical profile of Aitken particles according to Junge (1963) and Weickmann (1957). (i) under ambient conditions: (2) at standard temperature and pressure. (By courtesy of Academic Press and Jungel

The concentration of aerosol particles in the stratosphere was firstly measured by Junge (1963) by balloon fights over the Central U.S.A. He found (see Fig. 25) that the number of aerosol particles, in agreement with the Soviet data discussed above, does not change with altitude in the upper troposphere. This constant concentration is around 300 cm ~3. Above the tropopause the concentration rapidly decreases with increasing height. Since the character of the vertical profile plotted in Fig. 25 was more recently confirmed by several workers (e.g. Kaselau et aL 1974; Podzimek et al„ 1977), it can be considered acceptable for use in further studies. On the basis of the stratospheric concentration distribution, it is believed that particles in this atmospheric domain may be of tropospheric origin. However, it is also possible that stratospheric Aitken particles, formed in situ by gaseous reactions, coagulate to create the stratospheric aerosol layer consisting of large particles.

4.3.2 The size distribution

Since the size of atmospheric particles covers several orders of magnitude (see Subsection 4.1.1) the concentration alone is not sufficent to characterize atmospheric particles. For more complete aerosol characterization the size

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