Particle measurements conducted near a busy
electrified railway line in Zurich showed that the
main elements abraded by railway traffic were
iron and manganese originating from the wheel–
track interface, as well as copper from the overhead catenary system [53]. More than half of the
iron and manganese particles resulting from wheel
and track abrasion were in the coarse range. The
abrasion particles provided a small but
measureable contribution to local PM 10 concentrations [54]. However, the contribution of rail
transport on lines with a larger diesel share of
the traction could be much higher.
Resuspension
Another source of PM – the resuspension of material previously deposited on the road surface –
occurs as a result of tire shear, vehicle-generated
turbulence, and the action of the wind. Studies in
the United States have indicated that resuspension
is responsible for between 30% and 70% of total
PM 10 in urban areas [55–57]. Large contributions
of resuspension have also been observed in Germany [44, 58, 59] and the UK [60], albeit with a
large variation between locations.
Resuspension is a major concern in Scandinavian countries, especially in relation to the use of
studded tires and “road sanding.” Indeed, it can
provide a much larger contribution to PM 10 than
exhaust emissions, and also form a significant
fraction of PM 2.5 [61, 62]. An investigation in
Sweden revealed that PM 10 resuspension is highly
dependent on vehicle speed [63].
Modelling Transport Emissions
Estimates of emissions from transport are required
for various purposes. National inventories covering all sectors are part of the reporting obligations
of CLRTAP, the United Nations Framework Convention on Climate Change and, in the European
Union, Directive 2001/81/EC on National Emission Ceilings. At a more local level, emission
estimates are required for assessing the impacts
of policies and measures, and for input into air
quality modelling studies. Separate modelling
approaches have been developed for the different
transport modes. Most emission models are
empirical in nature, being based on data from
laboratory or real-world tests. However, it is
worth noting that such tests are not always
designed to deliver emission factors for modelling, and simulate only a small fraction of all
possible operational conditions [5].
Road Transport Models
Combustion In the simplest terms, the total
emission of a given pollutant during a given time
period is calculated as the sum product of specific
emission factors and quantities of activity:
E p ¼
X v¼n
v¼1
e p,v  T v
ð1Þ
where
E p ¼ total emission (e.g., in grams) of pollutant
p during the period
v ¼ vehicle category (with n different categories)
e p,v ¼ emission factor (e.g., in grams per kilometer
or liter of fuel burnt) of pollutant p from vehicle
category v
T v ¼ activity (e.g., in kilometers or liters of fuel)
of vehicle category v
The definition of emission factors that represent different aspects of vehicles and their operation forms a substantial area of research. Emission
models are generally classified in terms of how
they take vehicle operation into account. Here, the
term “vehicle operation” is used in a general
sense, and refers to a wide range of parameters
which describe the way in which a driver controls
a vehicle (e.g., average speed, maximum speed,
acceleration pattern, gear-change pattern), as well
as the way in which the vehicle responds (e.g.,
engine speed, engine load). The main types of
approach are aggregated emission factors,
average-speed models, traffic situation models,
multiple-regression models, modal models, and
instantaneous models.
Aggregated emission factors operate on the
simplest level, with a single emission factor
representing a general type of driving; the
Air Quality, Surface Transportation Impacts on
57
electrified railway line in Zurich showed that the
main elements abraded by railway traffic were
iron and manganese originating from the wheel–
track interface, as well as copper from the overhead catenary system [53]. More than half of the
iron and manganese particles resulting from wheel
and track abrasion were in the coarse range. The
abrasion particles provided a small but
measureable contribution to local PM 10 concentrations [54]. However, the contribution of rail
transport on lines with a larger diesel share of
the traction could be much higher.
Resuspension
Another source of PM – the resuspension of material previously deposited on the road surface –
occurs as a result of tire shear, vehicle-generated
turbulence, and the action of the wind. Studies in
the United States have indicated that resuspension
is responsible for between 30% and 70% of total
PM 10 in urban areas [55–57]. Large contributions
of resuspension have also been observed in Germany [44, 58, 59] and the UK [60], albeit with a
large variation between locations.
Resuspension is a major concern in Scandinavian countries, especially in relation to the use of
studded tires and “road sanding.” Indeed, it can
provide a much larger contribution to PM 10 than
exhaust emissions, and also form a significant
fraction of PM 2.5 [61, 62]. An investigation in
Sweden revealed that PM 10 resuspension is highly
dependent on vehicle speed [63].
Modelling Transport Emissions
Estimates of emissions from transport are required
for various purposes. National inventories covering all sectors are part of the reporting obligations
of CLRTAP, the United Nations Framework Convention on Climate Change and, in the European
Union, Directive 2001/81/EC on National Emission Ceilings. At a more local level, emission
estimates are required for assessing the impacts
of policies and measures, and for input into air
quality modelling studies. Separate modelling
approaches have been developed for the different
transport modes. Most emission models are
empirical in nature, being based on data from
laboratory or real-world tests. However, it is
worth noting that such tests are not always
designed to deliver emission factors for modelling, and simulate only a small fraction of all
possible operational conditions [5].
Road Transport Models
Combustion In the simplest terms, the total
emission of a given pollutant during a given time
period is calculated as the sum product of specific
emission factors and quantities of activity:
E p ¼
X v¼n
v¼1
e p,v  T v
ð1Þ
where
E p ¼ total emission (e.g., in grams) of pollutant
p during the period
v ¼ vehicle category (with n different categories)
e p,v ¼ emission factor (e.g., in grams per kilometer
or liter of fuel burnt) of pollutant p from vehicle
category v
T v ¼ activity (e.g., in kilometers or liters of fuel)
of vehicle category v
The definition of emission factors that represent different aspects of vehicles and their operation forms a substantial area of research. Emission
models are generally classified in terms of how
they take vehicle operation into account. Here, the
term “vehicle operation” is used in a general
sense, and refers to a wide range of parameters
which describe the way in which a driver controls
a vehicle (e.g., average speed, maximum speed,
acceleration pattern, gear-change pattern), as well
as the way in which the vehicle responds (e.g.,
engine speed, engine load). The main types of
approach are aggregated emission factors,
average-speed models, traffic situation models,
multiple-regression models, modal models, and
instantaneous models.
Aggregated emission factors operate on the
simplest level, with a single emission factor
representing a general type of driving; the
Air Quality, Surface Transportation Impacts on
57