benzene – have decreased so dramatically that they
are no longer considered to be a major threat to
human health. However, in many urban areas the
concentrations of NO 2 and PM 10 still frequently
exceed health-based limit values. According to the
European Environment Agency, in 2004, more than
20% of the European urban population were
exposed to ambient NO 2 concentrations above the
annual mean limit value (40 mg/m
3
) [19]. Furthermore, NO 2 and PM 10 concentrations at many roadside monitoring sites are not decreasing [19–21].
The problem is not confined to Europe; for example, a similar problem has been observed in Japan
[22]. Some possible reasons for this are explored
later in this entry. A further concern is that emissions of non-exhaust particles – especially those
arising from road vehicle tire and brake wear – are
not subject to legislation or control, and are
currently increasing in line with traffic growth
(bottom graph in Fig. 4).
Air Pollution Pathways
The links between transport, emissions, air pollution, and adverse impacts are not straightforward.
To illustrate this, the complex pathway from emissions to one specific type of impact – the health
outcomes of road transport pollution – is summarized in Fig. 5.
Many different pollutants are emitted by road
traffic, and the strength of the source depends on
the emission factors for the vehicles and the characteristics of the traffic (e.g., volume, speed and
composition). The emitted (primary) pollutants
are then dispersed in the ambient air according
0
1,000
2,000
3,000
4,000
5,000
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Passenger cars (billion pkm)
0
200
400
600
800
1,000
Other modes (billion pkm)
Passenger cars
Bus and coach
Two-wheel veh.
Railway
Sea
0
500
1,000
1,500
2,000
2,500
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Freight transport (billion tkm)
Road
Rail
Inland waterway
Sea
Air Quality, Surface Transportation Impacts on, Fig. 3 Passenger and freight transport in the EU-27 countries by
mode between 1995 and 2008. (Adapted from [17])
Air Quality, Surface Transportation Impacts on
51
are no longer considered to be a major threat to
human health. However, in many urban areas the
concentrations of NO 2 and PM 10 still frequently
exceed health-based limit values. According to the
European Environment Agency, in 2004, more than
20% of the European urban population were
exposed to ambient NO 2 concentrations above the
annual mean limit value (40 mg/m
3
) [19]. Furthermore, NO 2 and PM 10 concentrations at many roadside monitoring sites are not decreasing [19–21].
The problem is not confined to Europe; for example, a similar problem has been observed in Japan
[22]. Some possible reasons for this are explored
later in this entry. A further concern is that emissions of non-exhaust particles – especially those
arising from road vehicle tire and brake wear – are
not subject to legislation or control, and are
currently increasing in line with traffic growth
(bottom graph in Fig. 4).
Air Pollution Pathways
The links between transport, emissions, air pollution, and adverse impacts are not straightforward.
To illustrate this, the complex pathway from emissions to one specific type of impact – the health
outcomes of road transport pollution – is summarized in Fig. 5.
Many different pollutants are emitted by road
traffic, and the strength of the source depends on
the emission factors for the vehicles and the characteristics of the traffic (e.g., volume, speed and
composition). The emitted (primary) pollutants
are then dispersed in the ambient air according
0
1,000
2,000
3,000
4,000
5,000
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Passenger cars (billion pkm)
0
200
400
600
800
1,000
Other modes (billion pkm)
Passenger cars
Bus and coach
Two-wheel veh.
Railway
Sea
0
500
1,000
1,500
2,000
2,500
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Freight transport (billion tkm)
Road
Rail
Inland waterway
Sea
Air Quality, Surface Transportation Impacts on, Fig. 3 Passenger and freight transport in the EU-27 countries by
mode between 1995 and 2008. (Adapted from [17])
Air Quality, Surface Transportation Impacts on
51