Introduction

In recent years, stratospheric aerosols have received much attention due to the large role they play in atmospheric chemistry and climate. It was in the wake of the newly-discovered ozone hole (Farman et al., 1985) that the importance of stratospheric sulphates and polar stratospheric clouds were fully realized. Aerosols serve as surfaces and volumes which catalyze reactions which would not occur in the gas-phase. One important example at cold temperatures is,

$$\rm HCl + ClONO_2 \stackrel{\rm aerosol} \longrightarrow \rm Cl_2 + HNO_3$$ (8.1)

$$\rm Cl_2 + h\nu \longrightarrow \rm 2 Cl$$ (8.2)

which, following a photolysis reaction, converts chlorine from two reservoir species (which do not react with ozone) to a form which can catalytically destroy ozone. Stratospheric aerosols also perturb the radiation budget and can impact the global climate. They are efficient scatterers of solar radiation and act to increase the global albedo and hence cool the planet. Specific to the ER-2 flights, it is important to have an accurate representation of the aerosol for the forward radiative transfer modeling necessary to support photochemica