In this paper, the chemical characterization of PM10 and PM2.5 mass concentrations emitted by heterogeneous traffic in Chennai city during monsoon, winter and summer seasons were analysed. The 24-h averages of PM10 and PM2.5 mass concentrations, showed higher concentrations during the winter season (PM10=98μg/m3; PM2.5=74μg/m3) followed by the monsoon (PM10=87μg/m3; PM2.5=56μg/m3) and summer (PM10=77μg/m3; PM2.5=67μg/m3) seasons. The assessment of 24-h average PM10 and PM2.5 concentrations was indicated as violation of the world health organization (WHO standard for PM10=50μg/m3 and PM2.5=25μg/m3) and Indian national ambient air quality standards (NAAQS for PM10=100μg/m3 and PM2.5=60μg/m3).The chemicals characterization of PM10 and PM2.5 samples (22 samples) for each season were made for water soluble ions using Ion Chromatography (IC) and trace metals by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) instrument. Results showed the dominance of crustal elements (Ca, Mg, Al, Fe and K), followed by marine aerosols (Na and K) and trace elements (Zn, Ba, Be, Ca, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, Sr and Te) emitted from road traffic in both PM10 and PM2.5 mass. The ionic species concentration in PM10 and PM2.5 mass consists of 47-65% of anions and 35-53% of cations with dominance of SO42- ions. Comparison of the metallic and ionic species in PM10 and PM2.5 mass indicated the contributions from sea and crustal soil emissions to the coarse particles and traffic emissions to fine particles. © 2011 Elsevier B.V.