Different vehicles generate different pollutants. For
example, two-stroke motorcycles will emit more white smoke,
hydrocarbons and benzene than others (Japan Automobile
Manufacturers Association, 1990), thus they will contribute
significantly to roadside pollutant concentrations. During
observation periods, it was revealed that more than 80% of the
total motorcycle population at all monitoring stations used twostroke
engines. The predominance of two-stroke engines is one of
the significant factors for higher benzene concentrations in
ambient air.