Vertical transport of PM2.5 and PM10 and its source identification in the street canyons of Chennai metropolitan city, India

Chemical characterization of particulate matter (PM) measured along trafficked roads in Chennai city was performed during the winter season. Several heights, from 3 m to about 38 m above the ground level, and road geometries were taken into account. The daily average coarse (PM10) and fine (PM2.5) particles concentrations were in the range 72-110 (for PM10) and 34-57 mu g/m(3) (for PM2.5), depending on the site. Samples were analyzed in terms of inorganic ions using Ion Chromatography (IC) and elements by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Results indicated the dominance of SO42- followed by Na+, Ca2+, NO3- and Cl- ions in the coarse fraction; similarly, in the fine fraction ion concentrations decreased in the following order: SO42-, NH4+, K+ and Ca2+. Among the elements, crustal element (Al, Fe) and Zn concentrations were much higher (accounting about 90% of the total elemental concentration) than other toxic elements (Cr, Cu, Mn, Ni, Pb, Sn, Ti and V). No element showed a significant dependence on height, expect for calcium at site 'Velachery' which contributed significantly to the abundance of the coarse fraction mass. In order to identify the major sources of air pollution, the collected data were analyzed using Positive Matrix Factorization (PMF), allowing to highlight five dominant pollution sources/factors: secondary PM, road traffic, biomass burning, sea spray and crustal erosion. Overall, the present study provided a new insight for the source apportionment of monitored pollutants in the Chennai city.