The fate of sulphuric acid aerosol in the atmosphere

The phase diagram for (NH4)2SO4-H2SO4-H2O presented by Tang et al. ()978) was supplemented by tielines for the ammonia equilibrium concentration over liquied phase (Lee and Brosset, 1979). Such a complete diagram provides information essentially on the phase composition attained by a sulphuric acid droplet in equilibrium with the atmosphere. This composition can also be calcualted if the relative humidity (r.h.) and the concentration of ammonia (pNH3) of the atmosphere are known. Whether such calculations reflect the real conditions or not depends on the equlibrium adjustment, i.e. if it is sufficiently fast relative to the variation in temperature (t), r.h. and pHNO3 of the atmospehre. It was shown that the graphic correlation between r.h. and log pHNO3 provides direct information on the phases present on their eventual transformations. Such information obtained by mesurement of r.h. and pHNO3 was in good agreement with particle composition established by chemical analysis.