AN ANALYTIC-EXPRESSION FOR THE COMPOSITION OF AQUEOUS HNO3-H2SO4 STRATOSPHERIC AEROSOLS INCLUDING GAS-PHASE REMOVAL OF HNO3

An analytic expression is given for the composition and volume of stra tospheric HNO3-H2SO4-H2O aerosols in terms of the temperature and tota l amounts of H2O, HNO3 and H2SO4, taking into account conservation of HNO3. In contrast to previous parameterisations of equilibrium vapour pressures, the present scheme for calculating the aerosol composition does not require an iteration procedure, thus computation times are si gnificantly reduced, making it ideal for inclusion in large-scale atmo spheric models. Calculated composition are compared with the results o f a comprehensive thermodynamic model for all stratospheric conditions and maximum deviations are presented.