Particulate morphology and elemental characteristics: variability at middle Indo-Gangetic Plain

Airborne particulates were monitored at an urban location of middle Indo-Gangetic Plain (IGP) and subsequently analyzed for particulate diversity and mixing states. Exceptionally high particulate loadings were found both in case of coarser (PM10: 157.5 +/- 102.9 mu gm(-3), n = 46) and finer particulates (PM2.5: 92.5 +/- 49.8 mu gm(-3)). Based on particulate morphology and elemental composition, five different clusters of particulates namely tarball, soot, sulphur-rich, aluminosilicate and mineral species were found to dominate. Soot particles (0.1-5 mu m) were found to be partly coated, having voids filled by coating material without being completely engulfed. A specific type of amorphous, carbonaceous spherules was evident in wintertime fine particulates signifying emissions from biomass burning and wild fire. Traces of S, Na and Ca were found associated with carbonaceous agglomerates suggesting its metal scavenging behavior. Particle laden filters were further processed for metallic and water soluble ionic species to constitute aerosol composition. Coarser particulates were characterized with higher metallic species (9.2-17.8 %), mostly of crustal origin (Ca: 5.5 %; Fe: 1.6 %; Zn: 1.3 % and Na: 3.8 %) while PM2.5 also revealed their association with metallic components (6.0-14.9 %) having Ca (4.6 %), Fe (0.9 %) and K (0.8 %) as principle constituents. Ca, Na and NH4+ found to generate chloride and sulphate salts thus affecting particulate hygroscopicity. Elevated fractions of NO3- and K+ in PM2.5 signified contribution of biomass burning while presence of Cl- with carbonaceous aerosols having traces of Si and K denoted contribution of farming and burning practices. Black carbon aerosol exhibited significant seasonal variability (6.9-21.9 mu gm(-3)) which support larger association of carbonaceous aerosols in particle micrograph.