**2. Factors affecting aerosol characteristics over IGB**

Complex nature of aerosols over the IGB is mainly because the region is very diverse in topography, population distribution, meteorology and emission sources. Figure 3 shows unique topography of the IGB region, surrounded by the variety of aerosol emission sources and thus making it hotspot for aerosol research.

**Figure 3.** IGB region, showing unique topography surrounded by the variety of aerosol emission sources (Adopted after modification from personal presentation of William K. M. Lau on Aerosol, Monsoon Rainfall Variability and Climate Change).
