A previously published 2-D numerical model of the global dispersion of an eruption cloud in the stratosphere as a function of time assumed an instantaneous injection of the eruption cloud (the source function). New calculations show that the dispersion rate is quite insensitive to the manner of introducing the source function into the model, including spreading the eruption time over 10 days. Results obtained by flying through the eruption clouds from explosive volcanoes in Guatemala indicated that most of the sulfur in such clouds is SO2. If, as is generally believed, SO2 reacts with OH in the stratosphere, leading to the production of H2SO4 droplets, hugh explosive eruptions can deplete the stratosphere of OH for long time periods. The OH is thus controlled by the rate of O(1D) formation from ozone. By using the results from the 2-D dispersion model referred to above applied to the eruption cloud from the 1953 Agung eruption, and chemical kinetic rate constants, the 'e folding' residence time for sulfur dioxide conversion to sulfuric acid was estimated to be about 300 days. The Guatemala studies showed that the eruption clouds from explosive volcanoes contain large amounts of HCl. Unless much of this HCl is removed by rain accompanying the eruption, this HCl might be expected to have a marked influence on stratospheric chemistry as a result of the reaction OH+HCl→H2O+Cl. The volcanic HCl will probably remove OH much less rapidly than will SO2, and if the OH concentration is greatly decreased by the SO2, the above reaction may be too slow to be important.