The NASA GEOS-5 model was used to extend the MERRA reanalysis with five atmospheric aerosol components (sulfates, organic carbon, black carbon, desert dust, and sea-salt). The obtained eight-year (2002–2009) MERRA-driven aerosol reanalysis (MERRAero) dataset was applied to the study of aerosol optical thickness (AOT) trends over the Ganges basin and north-west Bay of Bengal (BoB) in the early post-monsoon season. In October, in the absence of aerosol sources in north-west Bay of Bengal (BoB), MERRAero showed increasing AOT trends over north-west BoB exceeding those over the east of the Ganges basin. Various aerosol components showed strong increasing AOT trends over north-west BoB. Our analysis showed that the AOT trends over north-west BoB were reproduced by GEOS-5, not because of MODIS AOT assimilation, but because of the model capability of reproducing meteorological factors contributing to AOT trends. The following factors contributed to the increasing AOT trend over the area in question in October: An increasing number of days when prevailing winds blew from land to sea, resulting in a drier environment and an increase in air pollution over north-west BoB; wind convergence was observed over north-west BoB causing the accumulation of aerosol particles over that region, when prevailing winds blew from land to sea.