One of the main sources of air pollution is traffic. To estimate the traffic contribution to air pollution the emissions are calculated from the vehicle fleet composition and vehicle emission factors (EF). Since the emission factors depend on vehicle type (cars, heavy and light duty), engine maintenance, driving environment (city, highway, regional roads) and weather, the emmision factors must be measured for in-use vehicles in actual traffic situations.
Two methods can be used to determine the so-called “real world” emission factors. The first method is the stationary method where EFs are calculated from the instantaneous rise of pollutants as a vehicle passes the measuring station. The second is the chasing method where vehicle emissions are measured by driving a mobile station behind the measured vehicle on the road.