VAPOR-PRESSURE MEASUREMENTS FOR THE H2SO4 HNO3/H2O AND H2SO4/HCL/H2O SYSTEMS - INCORPORATION OF STRATOSPHERIC ACIDS INTO BACKGROUND SULFATEAEROSOLS/

Vapor pressures over aqueous H2SO4/HNO3/H2O and H2SO4/HCl/H2O solution s have been measured for sulfuric acid contents ranging from 35 to 75 wt % at temperatures between 190 and 230 K. From the data, the Henry's law solubility constants for both systems are determined, and the equ ilibrium compositions of aqueous stratospheric aerosols are predicted as a function of ambient temperature and mixing ratios of H2O and HNO3 . The results indicate that, at the low temperatures characteristic of the stratosphere at high latitudes in the winter and spring, the HNO3 content reaches levels of the order of 10 wt % in the background sulf ate aerosols. The results also indicate that the amount of dissolved H Cl in the background sulfate aerosols is small when compared with diss olved HNO3 but may be significant for the production of Cl2 via the he terogeneous reaction between ClONO2 and HCl at low temperatures.