Assessment of Benzene and Toluene Emissions from Automobile Exhaust in Bangkok

The use of unleaded gasoline, together with an increase in the number of vehicles in Bangkok, has significantly influenced benzene and toluene concentrations in vehicular emissions and contributes to the air pollution problem. As a matter of practical necessity, a quick test program is done for the measurement of emission concentrations/rates for vehicles driven on the road. Exhaust emission measurement at idle mode was conducted in a fleet of 12 vehicles of different model years and manufacturers. The study revealed that the benzene and toluene concentrations in the exhaust effluent averaged 4.4–22.02 and 12.24–44.75 mg/m3, respectively for 1990–1992 cars and decreased to 0.76–4.14 and 0.89–6.26 mg/m3, respectively for 1994–1995 cars. In another study, exhaust emission measurement on a chassis dynamometer was carried out in a fleet of nine selected, in-use cars. It was observed that benzene and toluene emission rates were considerably higher—in the range of 70.84–85.82 and 354.15– 429.00 mg/km, respectively, for 1990–1991 model year cars. Lower benzene and toluene emission rates of 0.43–95.07 and 2.15–475.35 mg/km, respectively, were represented by newer cars with model years 1994–1995. These results indicated that there was a significant increase in benzene and toluene emission concentrations and rates with increasing car mileage and model year. The finding also revealed that only 28% of the tested vehicles complied to the approved emission standard.