Chemical and optical properties of PM2.5 from on-road operation of light duty vehicles in Delhi city

Abstract

This study reports emission factors of PM2.5, elemental carbon (EC), organic carbon (OC), ions, trace elements and mass absorption cross-sections (MAC) of aerosol emitted from the on-road operation of light duty vehicles of different vintages. A portable dilution system was used to achieve complete quenching of aerosol at near ambient condition. The particles were collected on the filters and analyzed for chemical and light absorbing properties of aerosol. The diesel-powered passenger cars emitted higher PM2.5 (56–356mgkm−1) with a large fraction of EC (37–65%), while emissions from gasoline (46–78mgkm−1), and CNG vehicles (33–34mgkm−1) were low and contained low EC (5–15%) and remarkably high OC (46–91%). The MAC of aerosols for diesel vehicles (32–208m2g−1 of PM2.5) were well explained by EC content (31–62%) and showed similarity with MAC values reported for wood fuel combustion in cooking stoves indicating the two sources cannot be resolved on the basis of light absorption properties in source apportionment studies. Ionic contributions to PM2.5 were highest for 4W-gasoline (11–19%) compared to 4W-diesel (7–11%), and CNG (9–10%). The abundance of ions such as Na+, Ca2+, SO42−, NO3−, and NH4+ could be due to use of lubricant oil and abrasive nature of engine of old vehicles. Trace elements (Al, Fe, Zn, Pb, and Cu) emitted from after-treatment devices, additives in lube oil, and wearing of engine components, were found to be 2–14%, 3–8% and 11–12% of total PM2.5 for 4W of diesel, gasoline, and CNG respectively. This study indicates that aerosol emissions from on-road vehicles show a strong dependency on vehicle maintenance, engine type and after-treatment techniques.