Experimental investigation and modelling of the physical and chemical absorption of gaseous phase SO2 into a single drop is described. In the experiment, the drop was suspended in a gas stream and the pH in the drop’s centre was measured by means of an antimony microelectrode. Experimental results were used for the modelling the internal circulation of the drop and for the estimation of the progress of chemical reactions which influence the pH of the system. The developed model is non-stationary and uses a rather simplified model of internal convection (circulation), yet it takes into account all important phenomena and parameters, e.g. the chemical composition of gaseous and liquid phases, gas velocity and drop geometry, drop exposure time, gas absorption and chemical reactions within the drop, and temperature.