Chlorine Chemistry of the Lower Stratosphere: Aircraft (ALIAS, ER-2) and Balloon (BLISSs) In-Situ Measurements of HC1,NO(sub 2), andN(sub 2)O for Testing Heterogeneous ChemistryStratospheric concentrations of HC1 measured in the northern hemisphere from the ER-2 aircraft are significantly lower than model predictions using both gas phase and heterogeneous chemistry, but measurements in the southern hemisphere are in much better agreement.