Chemical characteristics and deposition fluxes of dust-carbon mixed coarse aerosols at three sites of Delhi, NCR

Abstract

The present paper reports chemistry and fluxes of dust-carbon mixed coarse particles. For the purpose of this study, different carbonaceous fractions i.e. organic carbon ((OC), elemental carbon (EC) and carbonate carbon (CC) of atmospheric dust and their respective local soils were quantified at three sites of National Capital Region (NCR) of Delhi viz. Jawaharlal Nehru University campus (JNU), Connaught Place (CP) and Vishali area of Ghaziabad (GB). It has been observed that the OC and EC levels were approximately five to nine times higher in urban atmospheric dust than their corresponding soils, whereas CC levels were about three times higher than the corresponding soils. Average dustfall fluxes were significantly different at all the sites due to their different land-use patterns. At urban background site (JNU), the dust flux was lowest (172 mg/m2/day) followed by CP, a commercial site, (192 mg/m2/day) and GB, an industrial/residential area, (302 mg/m2/day). Similar to the dustfall pattern, the mean values of OC, EC and CC deposition fluxes were also observed to be lowest at JNU (9.2, 0.8 and 1.0 mg/m2/day, respectively) as compared to CP (12.2, 1.2 and 1.3 mg/m2/day, respectively) and GB sites (11.1, 1.1 and 1.4 mg/m2/day, respectively). Interestingly, unlike fine mode, different correlation pattern of OC and EC in coarse mode dust aerosols at three sites has suggested their independent deposition processes and source contribution. Fluxes of major water soluble inorganic ions (Na+, NH4+, K+, Ca2+, Mg2+, F−, Cl−, NO3− and SO42−) were also determined. Ca2+, Cl− and SO42− were found to be the major ionic species of water soluble fraction of the urban dust at all the sites. These interactions are corroborated by the morphology of the mixed aerosols. High levels of measured chemical species and their spatial distribution revealed close correspondence with the local emissions from transport, industries, biomass burning, road dust and construction activities etc.