Heterogeneity in pre-monsoon aerosol characteristics over the Indo-Gangetic Basin

- A large heterogeneity in aerosol loading is observed over the entire IGB region.
- Different types of aerosol loading over the region are observed during pre-monsoon.
- Western part is dominated by polluted dust while eastern by anthropogenic sources.
- Bi-modal nature of aerosol size distribution is observed over IGB during pre-monsoon.

Heterogeneity in aerosol characteristics was studied at five different locations over the Indo-Gangetic Basin (IGB) region during the pre-monsoon period (April-June 2011) using concurrent measurements from sun/sky radiometer, which is hypothesized to affect the Indian monsoon circulation and also the global climate system. Based on the measured aerosol products, distribution of aerosols and the associated optical properties were examined over the entire region. The pre-monsoon mean aerosol optical depth (AOD) was found to be maximum at Lahore (0.78) and Kanpur (0.68); however, a minimum AOD (∼0.6) was observed at Karachi, Jaipur and Gandhi College, with relatively high variability at Karachi and low at Gandhi College. On the other hand, a significant gradient in Angstrom exponent (AE) from Karachi (0.30) in the west to Gandhi College (0.98) in the east IGB region suggests relative dominance of coarse particles over the western part and fine particles at the eastern part of the IGB. Results are confirmed with the aerosol size distribution and the air mass back-trajectory analysis at all the stations. The corresponding pre-monsoon mean single scattering albedo (SSA) shows relatively higher value at Karachi (0.94), suggests relative dominance of scattering type particles. On the other hand, lower SSA, ranging from 0.85 to 0.92, was observed at the other stations, with the lowest value at Gandhi College (0.85), which suggests absorbing aerosol distributions over the region.