Sulphate Aerosols, Volcano and Resulting Impact on the Chemistry of Charged Atmosphere

The significant enhancement of sulphate aerosols above the tropopause can exert an extra forcing on the global climate system by altering the radiation balance and can also influence heterogeneous chemical reactions. Although charged species are in minority as compared to neutrals in the atmosphere, these are some processes where they may play a significant role under perturbed (volcanic) condition and would influence the neutral chemistry and can lead to ozone destruction through catalytic cycles (Beig, JGR, Vol. 105, August issue, 2000). This paper presents the results of coupled neutral-ion photochemical model to demonstrate that gas-phase sulfur chemistry played a vital role in perturbation of the stratospheric charged particles following the Mount Pinatubo eruption of June 1991. Immediately after the injection of 20 Mt of SO2 directly in the stratosphere, it is converted to gas phase H2SO4 vapor form which rapidly converted to H2SO4/H2O aerosols due to temperature controlled low vapor pressure theory. Available TOMS & SAGE satellite data are used as parameters in the model. Model results indicate that after about 2 to 3 months following the eruption, density of ultra-fine charged aerosols increasing several folds (~1500%) in the tropics for 20-30 km which is otherwise insignificant for normal cases. Domination of heavy charged species in the stratosphere reduced the mobility and conductivity of atmospheric medium which played a significant role in influencing the Global Electric circuit. Time series analysis indicates that the aerosol induced perturbation in charged atmosphere was started immediately after eruption with maximum around 3 months after the eruption in tropical lower stratosphere. It becomes weaker but unabated even after one year of eruption but settled down to background level after about 2 years.