Chemistry of size-segregated particles: study of sources and processes in N-NW India

PM0.95,PM0.95-1.5,PM1.5-3.0,PM3.0-7.2 and PM7.2-10 particles were collected simultaneously during summer season from Bikaner (BKR), Jhunjhunu (JHJ) and New Delhi (DEL) located in windward direction of south-westerly winds in north-northwestern, India and studied for mass concentrations and water-soluble inorganic ions (WSIIs). Organic carbon (OC) and elemental carbon (EC) were analyzed only for PM0.95. Particle mass concentrations, size distribution of WSIIs/elements suggested that winds selectively picked PM0.95 and PM3.0-7.2 from BKR and transported them downwind (DEL). Variations in WSIIs and elements were specific to ion/element, particle size and location(s). Secondary inorganic ions (SIN; NO3−, SO42−, NH4+) and Ca2+ were dominant ions compared to other ions and PM0.95 carried high WSIIs compared to other particles at all locations, due to more SIN formation in PM0.95. OC and EC increased significantly from BKR to DEL due to increasing combustion sources. Char-EC was more than soot-EC at all locations. Re-suspension of roadside/surface dust, and biomass burning were potentials sources of OC. Volatile organic compounds at DEL have resulted in formation of high secondary organic carbon. Major elements (MEs; Al, Ca, Fe, Mn, Ti) and trace elements (TEs; Ba, Sr, Zn, Cu, Cr, Pb, Co, Cd) were enriched in PM0.95 compared to other particles. Silica dilution effect resulted in lower enrichment ratios (ERs) of MEs with respect to Upper Continental Crust (UCC) whereas anthropogenic contributions for TEs, more in PM0.95, resulted in higher ERs. Homogenization effects on particle loading and composition were observed at BKR whereas lowering of wind speed and anthropogenic sources introduced heterogeneity at DEL.