To study the various chemical and dynamical properties of the lower atmosphere (i.e. the troposphere and the stratosphere) balloon-borne cryogenic air sampler experiments have been conducted from a tropical (Hyderabad, 17.5oN) and a midlatitude (Southern France, 44oN) station since 1987. Air samples are analysed at Max Planck Institute for Aeronomy and Physical Research Laboratory using various gas chromatographic techniques to obtain the vertical distributions of several ozone depleting substances and long-lived dynamical tracers etc. Observed, semi-theoretically derived, and numerically simulated (using Max Planck Institute for Chemistry (MPIC) 2D model) vertical profiles of trace gases are used to determine the stratospheric photochemical partitioning of the halogenated species into their organic and inorganic compounds. It is found that the abundance of organic chlorine (CCly) is higher in the tropics compared the midlatitude and the inverse is true for inorganic chlorine (Cly) species. MPIC 2D model results are also in good agreement with these estimations based on in situ measurements. The amount of CCly species is calculated to be about 3100, 3355, and 3645 pptv, respectively on March 27, 1987, April 9, 1990, and April 16, 1994 near the tropopause over Hyderabad. However, CCly concentrations do not show any discernible increase in the middle stratosphere. It can also be noted that the N2O-CCly correlation plots obtained for Hyderabad, GAP, and that during AASE II measurements are in fairly good agreement. The inorganic chlorine concentrations is found to be about 2200, 2700, and 3000 pptv on March 27, 1987, April 9, 1990, and April 16, 1994, respectively. Mixing ratio correlations of N2O-Cly apparently suggested an increase in the middle stratosphere during the period of measurements (1987-1994). These results imply slower removal of inorganic chlorine species from the stratosphere compared to the chlorine containing organic species. Similar characteristics have been observed for organic and inorganic partitioning of the brominated compounds in the lower stratosphere. These results also indicate that eventhough the loading of the halogenated organic species from the troposphere to the stratosphere have started decreasing since around 1994, the severity of halogen induced ozone depletion could continue in the later years.
Symposium on Interdisciplinary Issues in Atmospheric Chemistry