An important tool is air quality legislation (see
Chapter, ▶ “Air Quality Guidelines and Standards”), but it does not fall conveniently into the
prevention or mitigation categories. Although air
quality legislation acts as a driver for the development of pollution-reduction policies and technologies, and can thus be considered as “prevention,”
compliance with the legislation can only be determined from historical data, usually for the calendar year, such as the annual mean or the number of
days on which pollutant concentrations were
above a certain value. Neither does the legislation
specifically target transport.
Compliance with air quality standards for
PM 10 requires control of both fine and coarse
particles. As the two modes tend to have different
sources and formation mechanisms, different
types of control are required. The compounds
that are precursors to secondary particles also
need to be controlled. Primary fine particles from
combustion sources are subject to regulation. The
control of coarse particles is less straightforward
[118], as such particles arise from diverse natural
and anthropogenic disruption and attrition processes which are difficult to characterize (e.g.,
non-exhaust emissions, resuspension, dust from
industrial processes, quarrying).
As a result of reaction (2), O 3 levels near to
roads tend to be low. Thus, the limitation of local
traffic emissions would tend to lead to increased
O 3 concentrations at roadside locations. The control of O 3 depends ultimately on the control of
emissions of NO x and HC on a larger scale.
Prevention Measures
Some examples of prevention (i.e., emissionreduction) measures are listed in Table 1. The
list is not comprehensive, but provides an indication of the types of action which are currently
being considered. Two general approaches are
noted here: reducing emissions per vehicle and
reducing travel/transport activity, and several specific measures are available in each case. The
applicability of each measure to road transport,
rail transport, and shipping is also shown. Several
prevention measures are described in more detail
in the following paragraphs.
Emission Legislation In Europe, emission tests
are required at type approval for all new light-duty
vehicle models and for the engines used in heavyduty vehicles. Light-duty vehicles are tested using
a power-absorbing chassis dynamometer, as
shown in Fig. 8, whereas heavy-duty engines are
operated on a test bench. The sampling of exhaust
emissions is then performed as the vehicle or
engine progresses through a predefined driving
cycle.
Limit values are usually defined for CO, HC,
NO x , and PM in exhaust, as well as evaporative
emissions of VOCs. In the regulation of exhaust
particles, practically all worldwide emission standards are expressed in terms of the mass of total
particulate matter with no differentiation by particle size. Particle number emissions are included in
the latest European legislation.
The most advanced regulations are to be
found in the EU, the United States, and Japan.
The specific differences between the legislation
in different countries are too numerous to mention here, but the principles involved are broadly
similar and there is a general move toward harmonization. Moreover, the technology being
built into cars and trucks to comply with the
European, US, and Japanese standards is very
similar.
Over the course of several decades the limit
values for the pollutants in vehicle exhaust have
decreased (Fig. 12), and changes have been made
to the test method to make it more realistic. As a
result, manufacturers have been required to
develop increasingly effective emission-control
technologies (some effects of this were shown in
Fig. 4b). For example, the latest EU emission
standards for cars and heavy-duty vehicles require
large reductions in PM and NOx emissions, and
these will be achieved through the use of DPFs
and SCR.
Some examples of the progressive reduction in
the exhaust emission limits in several countries
(in terms of equivalence to the EU legislation)
are illustrated in Fig. 13. Most developing
countries lag behind the EU, although the gap is
narrowing and in some places it has been possible
to “leapfrog” standards. However, a prerequisite
for the introduction of advanced engine and
Air Quality, Surface Transportation Impacts on
67
Chapter, ▶ “Air Quality Guidelines and Standards”), but it does not fall conveniently into the
prevention or mitigation categories. Although air
quality legislation acts as a driver for the development of pollution-reduction policies and technologies, and can thus be considered as “prevention,”
compliance with the legislation can only be determined from historical data, usually for the calendar year, such as the annual mean or the number of
days on which pollutant concentrations were
above a certain value. Neither does the legislation
specifically target transport.
Compliance with air quality standards for
PM 10 requires control of both fine and coarse
particles. As the two modes tend to have different
sources and formation mechanisms, different
types of control are required. The compounds
that are precursors to secondary particles also
need to be controlled. Primary fine particles from
combustion sources are subject to regulation. The
control of coarse particles is less straightforward
[118], as such particles arise from diverse natural
and anthropogenic disruption and attrition processes which are difficult to characterize (e.g.,
non-exhaust emissions, resuspension, dust from
industrial processes, quarrying).
As a result of reaction (2), O 3 levels near to
roads tend to be low. Thus, the limitation of local
traffic emissions would tend to lead to increased
O 3 concentrations at roadside locations. The control of O 3 depends ultimately on the control of
emissions of NO x and HC on a larger scale.
Prevention Measures
Some examples of prevention (i.e., emissionreduction) measures are listed in Table 1. The
list is not comprehensive, but provides an indication of the types of action which are currently
being considered. Two general approaches are
noted here: reducing emissions per vehicle and
reducing travel/transport activity, and several specific measures are available in each case. The
applicability of each measure to road transport,
rail transport, and shipping is also shown. Several
prevention measures are described in more detail
in the following paragraphs.
Emission Legislation In Europe, emission tests
are required at type approval for all new light-duty
vehicle models and for the engines used in heavyduty vehicles. Light-duty vehicles are tested using
a power-absorbing chassis dynamometer, as
shown in Fig. 8, whereas heavy-duty engines are
operated on a test bench. The sampling of exhaust
emissions is then performed as the vehicle or
engine progresses through a predefined driving
cycle.
Limit values are usually defined for CO, HC,
NO x , and PM in exhaust, as well as evaporative
emissions of VOCs. In the regulation of exhaust
particles, practically all worldwide emission standards are expressed in terms of the mass of total
particulate matter with no differentiation by particle size. Particle number emissions are included in
the latest European legislation.
The most advanced regulations are to be
found in the EU, the United States, and Japan.
The specific differences between the legislation
in different countries are too numerous to mention here, but the principles involved are broadly
similar and there is a general move toward harmonization. Moreover, the technology being
built into cars and trucks to comply with the
European, US, and Japanese standards is very
similar.
Over the course of several decades the limit
values for the pollutants in vehicle exhaust have
decreased (Fig. 12), and changes have been made
to the test method to make it more realistic. As a
result, manufacturers have been required to
develop increasingly effective emission-control
technologies (some effects of this were shown in
Fig. 4b). For example, the latest EU emission
standards for cars and heavy-duty vehicles require
large reductions in PM and NOx emissions, and
these will be achieved through the use of DPFs
and SCR.
Some examples of the progressive reduction in
the exhaust emission limits in several countries
(in terms of equivalence to the EU legislation)
are illustrated in Fig. 13. Most developing
countries lag behind the EU, although the gap is
narrowing and in some places it has been possible
to “leapfrog” standards. However, a prerequisite
for the introduction of advanced engine and
Air Quality, Surface Transportation Impacts on
67