and Shao 2009b). Silicate minerals are abundantly present
in Pune (as depicted in Fig. 8) which can act as surrogate
for the sulfurization. However, the calcite or dolomite or
Ca-rich particles can be of importance to absorb the acidic
materials. These particles are predominately in the fine
fraction and therefore round in shape. In recent years,
sulfurization on the surface of particles has also been
reported by Lu Senlin et al. (2006). Figure 8 shows the
particles enriched with Ca and S. Sulfur cluster often with
sharp edges are mainly composed of CaSO4 (gypsum). The
formation of this mineral may arise from the heterogeneous
oxidation of SO2 on the existing mineral particles surface
in the atmosphere. The internal and external mixing/reaction
result the aggregated particles of gypsum after the
evaporation of drops (sharp edges of gypsum seen in the
Fig. 8). Type of aggregation of these particles is important
because it affects radiative properties of the aerosols and