Inhalable particles (PM10) in Lahore, Pakistan, during a high polluting spring episode in 2006 were collected and analyzed for the ambient concentrations of organic and element carbon (OC, EC) and more than one hundred organic species. High PM10 mass concentrations, averaging 459 µg/m3, were characterized by extremely high concentrations of mobile source related organic compounds including hopanes and PAHs. Source apportionment of PM10 OC, EC and mass was performed using molecular marker based CMB receptor model. Results showed that traffic pollution, including exhaust from gasoline or diesel powered vehicles, was the predominate source of carbonaceous aerosols. Gasoline powered vehicles plus diesel exhausts contribute 47.5%, 88.3% and 15.4% of measured inhalable particulate OC, EC and mass, respectively. Though the contribution is not quantitatively calculated in this study, dust was estimated as another important source of PM10, which is a significant contributor to coarse phase pollutions. Even compared to other mega-cities like Beijing, Mexico City, and Los Angeles, the motor vehicle associated pollution in Lahore was found to be very large. Other sources of carbonaceous aerosols were quantified including wood smoke, vegetative detritus, natural gas combustions and have relative small contributions compared with the traffic pollutions.