Global distribution of solid and aqueous sulfate aerosols: effect of the hysteresis of particle phase transitions

We developed, for the first time in Eulerian modeling framework (e.g., GEOS-Chem), a prognostic approach to simulate the distribution of solid and aqueous sulfate aerosols. The simulation explicitly accounts for the composition-dependent hysteresis of particle phase transitions.

The figure above shows the annual zonal means of (a) the extent of neutralization X (= [NH4+]/2[SO42-]), (b) the relative humidity, and (c) the mass fraction of solid sulfate particles. The dominance of solids in the upper troposphere arises in part from high sulfate neutralization, reflecting in our simulation a low retention efficiency of NH3 upon cloud freezing. High sulfate neutralization is consistent with the few available observations in the upper troposphere.