This paper presents the characteristics of particulate matter (PM) mass concentrations (PM10, PM2.5 and PM1) emitted from heterogeneous traffic in Chennai city during monsoon, winter and summer seasons of the year 2007-2009. The heterogeneous traffic characteristics at the study region indicated dominance of 2-wheelers (58%) followed by the 4-wheelers (29%), 3-wheelers (7%), light commercial vehicle (LCV = 2%) and heavy commercial vehicle (HCV = 4%). The vintage analysis of vehicles showed that 11, 24, 35 and 30% of the total vehicles were 15, 10, 5 and <5 years old vehicles, respectively (75% of LCV and 70% of HCV were older than 10 years and 82% of 2W, 85% of 3W, 79% of 4W were less than 10 years old). The travel demand on weekdays at the study site revealed that 60% of the traffic in the morning peak hours was due to school and office trips and 40% was due to the business trips. During the weekends the peak rush hours traffic was dominated by travel demand (90%) due to tourists and pleasure trips. At study region, the PM10 comprised a large fraction of PM2.5 (56% of PM2.5 and 44% of PM1), while PM2.5 comprised a large proportion of PM1 (81%). The estimated PM2.5/PM10 ratios for monsoon, winter and summer seasons were ranged between 0.44-0.62, 0.66-0.76 and 0.62-0.73, respectively. The high PM2.5/PM10 ratios (R2 = 0.92-0.98) during peak hour indicated significant contribution from the vehicular emissions. Further, it was found that the PM10, PM2.5 and PM1 concentrations at the study site followed similar trend of 2W, 3W, 4W and HCV during morning peak hour traffic. The analysis of 24-hr average PM10, PM2.5 and PM1 concentrations showed maximum during monsoon (188.75 ± 71.75, 83.91 ± 33.18, 65.81 ± 28.47 μg/m3) and winter (134.58 ± 64.55, 72.95 ± 39.27, 59.00 ± 31.15 μg/m3) and minimum during summer (75.96 ± 43.15, 42.16 ± 19.76, 31.40 ± 16.05 μg/m3) seasons. The 24-hr average PM10 and PM2.5 indicated maximum violations of Indian national ambient air quality standards (NAAQS for PM10 = 100 μg/m3 and PM2.5 = 60 μg/m3) during winter and monsoon seasons and minimum during summer season. Further, PM10 and PM2.5 concentrations were well above the prescribed 24-hr average world health organization (WHO) standards (PM10 = 50 μg/m3; PM2.5 = 25 μg/m3).The PM chemical characterization indicated the dominance of soil based crustal elements (74%) - Al, Ca, Fe and Mg, salt based components (16%)-Na and K, and the other trace elements (10%) such as B, Ba, Cd, Co, Cr, Cu, Ga, Mn, Mo, Ni, Pb, Rb, Se, Sr, Te, V and Zn. The percentage composition of different group of elements indicates traffic as the main source of PM emission at the study site. The ion analysis showed presence of more anions (36-82%) than the cations (18-64%). SO42- and Mg2+ were major constituents. © 2011 Elsevier Ltd.