Source Apportionment of PM2.5 Using a CMB Model for a Centrally Located Indian City

Samples of PM2.5 were collected sequentially for 24 hours during the last week of September to mid February 2009-10 at three locations representing residential (R), commercial (C) and industrial (I) sites in Nagpur city to determine their chemical composition and estimations of the sources contributing to them. Two receptor models were used for the source apportionment viz. enrichment factors (EF) to differentiate crustal and non-crustal sources, whereas chemical mass balance (CMB 8.2) was used to identify and quantify the major sources contributing to PM2.5. The ambient mass concentrations and chemical compositions of PM2.5 with respect to ionic species (Na+, NH4+, K+, Ca2+, F-, Cl-, NO3- and SO42-); carbonaceous species (organic and elemental carbon) and trace metals (Al, Ba, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si and Zn) were determined. The most abundant chemical species were OC, EC, SO42-, NO3-, NH4+, K+ and trace metals (Al, Fe, Si, Mg, and Cu) at all the sites. Findings of EF showed the anthropogenic origin of Cd, Ni, Pb, Cu, Fe and Zn, whereas Ba, Cr, Mg, Mn, and Si were contributed from crustal sources. On the other hand, results of CMB using source profiles developed in India for non-vehicular and vehicular sources revealed that vehicular emissions were major contributing sources 57, 62 and 65%; followed by secondary inorganic aerosol 16, 12, 16%; biomass burning 15, 11, 9% and then by re-suspended dust 6,10, 7% at R, C and I sites, respectively. This study showed that while the sources at all three sites were mostly consistent, the percent contributions of these varied among the sites as per the intensity of ongoing activities at the receptor sites.