**6.2. Source identification of natural and anthropogenic aerosols**

20 Will-be-set-by-IN-TECH

**Figure 9.** Seasonal variation of vertical distribution of aerosol extinction coefficient obtained from

hill-top region are considered and defined as the 'background aerosols'. The vertical profile of aerosols indicate that these background aerosols are less influenced from these locally produced anthropogenic aerosols. Therefore, the aerosol properties observed over Mt. Abu are assumed to represent those of the background aerosols over semi-arid region of western

The estimation of natural and anthropogenic aerosols over this background site is a challenging task because many aerosol compositions have both origins. For example, sulphates are mainly considered as anthropogenic components over urban regions as they

CALIPSO observations. The horizontal dashed line at 1.7 km is the altitude of Mt. Abu.

**6. Natural and anthropogenic background aerosol properties**

**6.1. Estimation of natural and anthropogenic aerosols**

India.

Seven days air parcel back trajectories are considered to identify the possible source regions of the natural and anthropogenic aerosols at Mt. Abu. The back-trajectories during premonsoon and winter are shown in Figure 11(a) and (b), respectively. Air parcels are mainly coming from IGP during winter and the heights of the trajectories are within 2 km. Ground based observations show that BC values at Mt. Abu are higher during winter and it is also clearly seen that there is long-range transportation of anthropogenic aerosols like BC from IGP within the boundary layer height. On the other side, air parcels are direction during premonsoon season. The heights are also greater than 3 km. Earlier chemical analyses report that dust concentration during this season is maximum of about 80% (in mass) of the total aerosols [39]. Therefore, one can easily conclude by these trajectories that the source of these dust aerosols is the nearby desert region. The back-trajectory analysis indicates that there is significant contribution of IGP during winter enhancing anthropogenic aerosols and that by nearby arid region during premonsoon increasing natural dust aerosols.
