Physical analogs and performance of a box model for composition and growthof H2SO4/H2O and HNO3/H2SO4/H2O aerosol in the stratosphere

A physical box model simulating the aerosol particle evolution along air ma ss trajectories is developed to provide a tool for interpreting the local o bservations of stratospheric aerosols (i.e., polar stratospheric clouds). T he model calculates the composition and the size distributions of H2SO4/H2O and HNO3/H2SO4/H2O liquid droplets. The parameterization of the physical p rocesses affecting the dynamics of HNO3 and H2SO4 solid hydrates and ice pa rticle size distributions is also included, but not used. This work is rest ricted to some speculations about the liquid to solid transition, according to existing theories. The evolution of liquid particles is simulated takin g into account nucleation, diffusive condensation/evaporation and coagulati on. This paper reports the physical and numerical details of the model, whi ch are discussed within the framework of the current understanding of the s tratospheric aerosol physics. Performance and limitations of the model are discussed on the basis of the evolution of particle size, and composition a long synthetic air mass thermal histories. Size distributions and size-depe ndent acid weight fractions of the liquid stratospheric aerosols consisting of HNO3/H2SO4/H2O are calculated in the cases of air mass thermal historie s with different cooling rates and with rapid temperature fluctuations. (C) 1999 Elsevier Science Ltd. All rights reserved.