Three-body association rate coefficients have been measured as a function of temperature for the clustering of HCl to HSO4-(H2SO4)m (HNO3)n ions for m=0--3 and n=0 and 1. The temperature coefficients of these clustering reactions were found to increase with increasing cluster size in agreement with studies on other systems. A total of three ligands was found to bond strongly to HSO4-. We also measured the rate coefficients for NO3- clustering to HNO3 as a function of pressure. This rate was found to saturate at a value of 2.6¿10-10 cm3 s-1 at a pressure of about 0.3 torr. The data were used to check the identities of some of the ions observed in the stratosphere and to predict the abundances of other ions that have not yet been observed. HNO3 concentrations derived from in situ ion composition measurements have been corrected to account for the saturation of the rate coefficient at a value less than 10-9 cm3 s-1. The corrected concentrations do not change much at 34 km but increase by a factor of almost 2 at 40.8 km. This result is in better agreement with model calculations.