Chemical Characterization of Fine Particulate Matter in Gasoline and Diesel Vehicle Exhaust

This study investigated the chemical composition (carbonaceous species, water-soluble ions and metal elements) of fine particulate matter (PM2.5) emitted by gasoline and diesel vehicles. The emission factors of PM2.5, total hydrocarbons (THC), carbon monoxide (CO) and oxides of nitrogen (NOx) were also determined. The emission measurements were performed for four gasoline and four diesel vehicles on a dynamometer with a constant volume sampling system. Vehicles having larger engines and higher accumulated mileages had higher emission factors of gaseous pollutants. Moreover, the average emission factor of NOx was about 30 times higher for diesel vehicles than for gasoline vehicles. The average PM2.5 emission factors for gasoline and diesel vehicles were 1.57 mg km–1 and 57.8 mg km–1, respectively. The ratio of organic carbon to elemental carbon (OC/EC) was found to be a good indicator of gasoline vehicle emissions (OC/EC > 1) and diesel vehicle emissions (OC/EC < 1). Among water-soluble ions, Ca2+ and SO42– had the highest contribution to PM2.5 emitted by gasoline vehicles, while NO3–, SO42– and Ca2+ had the highest contribution to PM2.5 emitted by diesel vehicles. Na, Ca, Fe and Zn were the top four metal elements in terms of their contributions to PM2.5 mass for both types of the vehicles, while Cd, Cr, Pb and Sb were some of the toxic metal elements detected in PM2.5.