Measurement based Analysis of Physical, Chemical, Morphological, and Optical Properties of Dust over the Indo-Gangetic Basin

A study is conducted in campaign mode at Kanpur (26.52N, 80.23E), India, during April to July 2011, to study the physical, chemical, optical, and morphological properties of dust over the Indo-Gangetic basin. The main objectives are to study various characteristic properties of mineral dust, modification in these properties due to long-range transport and mixing with pollution, and to identify dust proxies based on chemical analysis. The duration of campaign witnesses heavy dust storms and the onset of South West Indian Monsoon. AERONET measured Aerosol Optical Depth (AOD) at 500 nm during April to June is observed to vary from 0.2 to 1.2. The aerosol types encountered are classified among Dust, Polluted Dust, Burning, and Continental categories which represent the prevalent aerosol scenario in the region during this period. As reflected in the measured aerosol size distributions, burning generated aerosols have bimodal distribution, whereas Dust and Polluted Dust have trimodal distribution. Based on HYSPLIT calculated 10-day backtrajectory analysis, Nepal and the desert regions of NW India are identified as sources of aerosols associated with burning events and dust dominated days respectively. MPLNET derived aerosol extinction profiles show that during dusty days, particles reach up to a height of ~5 km. In June and July, surface measured Absorption Coefficient reduced nearly half the value in April and May, while surface measured Extinction Coefficient almost gets doubled. From pre-monsoon to monsoon period, SSA increased from 0.76 to 0.95, while Bext showed three times growth. High values of SSA (Greater than average, 0.83-0.87) are observed on dust events. SEM images of collected aerosol samples show different particle shapes eg, rhombic, platelets, and parallelepiped. XRF analyses of aerosol samples show the presence of Al, Ti, Fe, Ca, Mg, and K in PM10 samples collected on dust dominated days, and high S content in PM2.5 for burning events. A noticeable characteristic of this analysis is higher Ca/Fe ratio and high K/Al ratio for dust and burning events, respectively. Dominance of SO4_2- is observed in ion analysis (Na+, NH4+, K+, Ca2+, Mg2+, Cl-, NO3-, SO4_2-) of the PM2.5 and PM10 samples as per the average concentration.