Air and health impacts of diesel
emissions
(S230)
Version: 5
January 2016
KNOWLEDGE
ANALYSIS
Copyright
© RAIL SAFETY AND STANDARDS BOARD LTD. 2016 ALL RIGHTS RESERVED
This work comprises, in part, of a review of existing works published by others.
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Published: January 2016
Cover pictures: ©Shutterstock, www.whatisepigenetics.com, ©Stephen Craven,
www.bombardier.com
Scope of this knowledge search
As a quick knowledge search, this report provides key bibliographical references and
limited analysis. It is intended to inform decisions about the scope and direction of
possible research and innovation initiatives to be undertaken in this area. It does not
provide definitive answers on this issue; and is not intended to represent RSSB’s view on
it.
The search may only include what is available in the public domain.
It has been conducted by a team with expertise in gathering, structuring, analysing both
qualitative and quantitative information, not by specialists in the field. Experts in railway
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to the limited time available. Industry and experts in this field are very welcome make
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For further information or background to this report, please contact RSSB Knowledge
Management and Systems at knowledgesearch@rssb.co.uk.
Executive Summary
This report is a brief summary of the current knowledge of the health effects of diesel
exhaust emissions, the impact of the railway industry’s activities on diesel pollution, and
some of the initiatives the industry has taken to mitigate these effects. Diesel traction is
a significant form of motive power on the Great Britain railway network and will remain
so for the foreseeable future. Furthermore, because diesel services are concentrated on
specific routes, there are pollution hotspots – especially enclosed terminal stations.
The health risks of diesel exhaust have been well researched. It is known that it can
cause irritation to the eyes and respiratory system, which may exacerbate pre-existing
conditions including asthma. The greater concern, however, has been with the
carcinogenicity of the components of the exhaust although studies suggest that
individuals with occasional or limited exposure are not significantly at risk.
Another particular concern relates to nitrogen dioxide, present in diesel exhaust, which
could be responsible for increasing the contribution of air pollution to the UK’s overall
death rate from 5-9% to 10-18%. Nitrogen dioxide contributes to the development of
heart disease and chronic obstructive pulmonary disease. Testing for nitrogen dioxide is
therefore an important part of monitoring programmes.
Relatively little work has been done to monitor diesel exhaust emissions from the
railway, most efforts being directed towards road transport. Where monitoring
exercises have been carried out, great care has been needed to ensure that rail
emissions can be isolated from other pollution sources. Possibly the most
comprehensive study was carried out by King’s College London at two sites adjacent to
main line railways in the boroughs of Ealing and Islington. This compared actual levels of
emissions with modelled data. The unexpected findings showed that rail emissions
were significantly lower than from road traffic and that trains were not making a major
contribution to local particulate matter and nitrogen dioxide concentrations.
Other monitoring exercises have been carried out at Edinburgh Waverley and
Paddington. The former found that although pollutant levels were higher than in the
surrounding streets, they were well below occupational exposure limit levels; at
Paddington further work will be needed to obtain an accurate overall picture.
Current electrification schemes will reduce the use of diesel traction on the network and
encouraging trials with battery powered trains suggest that the benefits can be
extended to non-electrified branch lines. Where diesel locomotives continue to be in
use, the industry is moving towards lower emissions to comply with European legislation
and applying stop-start technology to reduce engine idling. Idling has been reduced by
providing shore supplies at stations or on-board generators to provide hotel power
when locomotives are shut down. Finally in enclosed locations where diesel fumes
remain a problem, sophisticated ventilation systems have been installed.
3
Table of Contents
1
INTRODUCTION ...................................................................................................................................... 5
2
HEALTH EFFECTS OF DIESEL EMISSIONS ................................................................................................. 5
2.1 Carcinogenicity ....................................................................................................................... 5
2.2 Other health effects ............................................................................................................... 7
3
DIESEL EMISSIONS FROM RAILWAY SOURCES ........................................................................................ 8
3.1 UIC research ........................................................................................................................... 8
3.2 Other research ...................................................................................................................... 11
4
UK CASE STUDIES ................................................................................................................................. 12
4.1 Ealing and Islington............................................................................................................... 12
4.2 Edinburgh Waverley ............................................................................................................. 14
4.3 Paddington ........................................................................................................................... 16
4.4 Paddington (CIRAS report).................................................................................................... 17
5
RAILWAY INDUSTRY INITIATIVES.......................................................................................................... 18
5.1 Eliminating Emissions ........................................................................................................... 18
5.2 Reducing Emissions .............................................................................................................. 19
5.2.1 Low emission diesel engines ......................................................................................... 19
5.2.2 Low sulphur fuel ............................................................................................................ 19
5.2.3 Stop-start Technology ................................................................................................... 20
5.2.4 Idling engines at stations .............................................................................................. 20
5.3 Mitigating Emissions ............................................................................................................. 21
6
CONCLUSION ........................................................................................................................................ 22
7
BIBLIOGRAPHY ..................................................................................................................................... 23
4
1 Introduction
This report examines the current state of knowledge on the health effects of diesel
exhaust emissions and how this understanding affects the railway industry in Great
Britain. There is evidence that long-term exposure to diesel exhaust increases the risk of
some types of cancer, and even short term exposure can cause irritation to the eyes and
respiratory tract.
In 2012 the World Health Organisation’s International Agency for Research on Cancer
reclassified diesel exhaust as a ‘definite carcinogen’, which has inevitably caused some
disquiet amongst those working in environments where diesel engines operate, as well
as the public living close to busy roads and railways. Although the actual risk may not be
significant for most individuals with limited levels of exposure, the rail industry is keen
on having a deeper understanding of the processes involved and on ensuring that
suitable mitigation measures are in place where necessary.
2 Health effects of diesel emissions
2.1 Carcinogenicity
According to the Health and Safety Executive (HSE) there is consistent but limited
evidence of an increase in the incidence of lung cancer for people engaged in
occupations with significant exposure to diesel engine exhaust emissions for more than
20 years. This is likely to primarily affect the likes of fitters in diesel depots whose
exposure is continuous for most of their working day.
The HSE reports a review undertaken by the World Health Organisation in 1989 which
concluded that the evidence was limited for carcinogenicity among occupational groups
exposed to high cumulative levels of diesel exhaust, but that there was ‘sufficient’
evidence for carcinogenicity from studies of animals exposed to whole diesel engine
exhaust. The review concluded that diesel engine exhaust was therefore ‘probably
carcinogenic’ to humans, although the overall evidence was not convincing.
The Department of Health’s Committee on Carcinogenicity examined the subject in 1990
and reached a broadly similar conclusion; diesel exhaust was carcinogenic to rats and
might therefore be carcinogenic to humans given sustained exposure levels over a long
period. The same committee looked at more recent studies in 1996 and reached two
conclusions which were accepted by the HSE:
 The carcinogenicity of diesel exhaust emissions appeared to be specific to rats, caused
by overloading the lung clearance mechanisms with particulate, an effect not
relevant to humans.
5
 Epidemiological evidence indicated a carcinogenic effect from sustained occupational
exposure over periods exceeding 20 years – but there was no evidence of increased
risk at lower cumulative exposure levels.
More recent work in Germany has examined the reasons for the long term
carcinogenicity of diesel exhaust, finding that it may be associated with the particulate
component, in particular the inert core of elemental carbon, although organic
substances absorbed onto the carbon particles are also important.
In view of this the HSE advises its inspectors that if the carcinogenicity of diesel exhaust
is raised in workplaces by employers or employees to say that the HSE is aware of the
link but that the risk is very slight and does not justify being classified as a carcinogen for
regulation purposes. This does not mean, of course, that diesel exhaust is not
considered undesirable but the focus should be less on measuring particulates and,
possibly, towards measuring aldehydes (formaldehyde and acetaldehyde) although it is
acknowledged that research is needed in this area.
A detailed study was carried out in the USA in 2004 on the incidence of lung cancer in
railroad workers exposed to diesel exhaust. This found that there was a greater
incidence of lung cancer mortality among long-term workers in jobs associated with
diesel powered trains than would normally be expected. The results were not clear cut,
however, the authors noting that exposure over the study period (1959-1996) would not
have been at a constant level because diesel engine technology had improved, making
locomotives gradually ‘less smoky’. There was also concern that the results could be
skewed by the ‘healthy worker effect’, which, in simple terms, is the statistical
aberration whereby employed workers are healthier than the population as a whole
because the chronically sick are not in employment.
In 2012 research findings were published based on a larger population than previous
studies. The paper examined the case of lung cancer and diesel exhaust among 12,315
workers in eight non-metal mines. The results were adjusted to take into account the
effects of smoking and other known causes of lung cancer. Statistically significant
increasing trends in lung cancer risk were found for heavily exposed workers. From
these data the authors rather cautiously concluded that ‘diesel exhaust exposure may
cause lung cancer and may represent a potential public health burden’. This statement
therefore widened concerns among workers in facilities with high levels of diesel
exhaust emissions and the wider public.
The implications of this research were discussed by Cancer Research UK on its website1.
It asked the question: ‘should we be worried?’ Unsurprisingly, given the uncertain
nature of the research findings, the answer was equivocal, suggesting that while there
was likely to be some risk to the public, especially those living in cities, it was important
1
http://scienceblog.cancerresearchuk.org/2012/06/14/diesel-fumes-definitely-cause-cancershould-we-be-worried/
6
not to overreact. Other causes of cancer including tobacco, alcohol and excess
bodyweight were much more significant.
All this work, and the associated uncertainties, concentrated on the effects of
particulates in diesel exhaust. These soot particulates have organic substances
adsorbed on to their surfaces, described as ‘polycyclic aromatic hydrocarbons’; when
inhaled these can cause damage to lung cells potentially leading to cancer development.
They might directly damage the cells’ DNA or they might become lodged in the lungs
causing long-term inflammation. Inflammation can result in an increase in the rate at
which cells divide; if any of these pick up random mutations they are therefore more
likely to grow and spread.
2.2 Other health effects
Other effects of diesel exhaust emissions identified by the HSE include irritation of the
eyes and the respiratory tract. This leads to coughing, increased sputum production and
breathlessness. There is also strong epidemiological evidence of a link between urban
particulate atmospheric pollution and increases in overall morbidity and mortality
among the general population, mainly affecting the elderly and people with a preexisting respiratory illness, although the precise contribution of diesel exhaust emissions
to these effects is uncertain.
The HSE does impose exposure limits on individual gaseous components of diesel
exhaust but these are generally found at low levels – insufficient to require mitigating
controls. It is uncertain as to which specific components cause irritancy and this effect
may result from a synergy of more than one, so it is not possible to control health
effects by reducing any single component. The HSE therefore recommends that, for the
workplace, diesel exhaust should be considered as a substance in its own right and
appropriate controls put in place – good ventilation being an obvious example.
However, a report published in The Sunday Times in 2014 raised the issue of nitrogen
dioxide contained in diesel emissions, a separate issue from particulates that had
previously been the focus of research2. The newspaper quoted Professor Frank Kelly,
chairman of the government committee on the medical effects of air pollutants, who
said that the ‘addition of the impact of NO2 to mortality rates would increase air
pollution’s contribution to the total death rate from 5-9% across the UK to 10-18%’.
This, it was claimed, equated to 60,000 deaths. Nitrogen dioxide is a contributory factor
to the development of chronic illnesses such as heart disease and chronic obstructive
pulmonary disease. The report went on to note that while particulate levels had been
declining, NO2 concentrations remained at a high level, suggesting that nitrogen dioxide
was now having the greater impact on public health.
2
Sunday Times 30 November 2014
7
The worst effects of nitrogen dioxide pollution occur where road traffic levels are at
their greatest, with London having the highest mortality rate. A report published by the
London mayor’s office put the number of deaths from this cause at 2,600 per year.
3 Diesel emissions from railway sources
It should be noted that the tests and surveys mentioned in the following sections were
conducted before ultra-low-sulphur diesel (ULSD) was introduced in GB railways, and do
not capture the improvements realised since. The EU's Fuel Quality Directive
(2009/30/EC) has introduced a requirement for all gas oil for use in Non Road Mobile
Machinery (NRMM) to be virtually sulphur-free (sulphur content not exceeding 10 parts
per million). In the UK, the directive was transposed such that NRMM met this
requirement by 1 January 2011. Under an EU derogation, fuel for rail locomotives has
met the sulphur free requirement from 1 January 2012. The UK's gas oil standard BS
2869 has been updated to reflect these changes.
3.1 UIC research
In 2006 the UIC published a report on rail diesel emissions. It noted initially that
railways’ environmental benefit over other modes of transport is a ‘vital precondition in
ensuring social and political support’ and that although road transport was considered
to be the main polluter, rail pollutant emissions were ‘increasingly attracting the
attention of public and authorities alike’. At the time European legislation had set limit
values for NOx and PM10 emissions from railway locomotives3.
Rail’s share of overall emissions was estimated to be 1-3%. The UIC analysis showed
insignificant pollutant contributions by rail even at busy locations. The most relevant
contributions (but still below the limit values) were at major terminal stations.
However, railway contributions to nitrogen dioxide concentrations were generally
observed to be more significant than to particulate concentrations.
The UIC went on to consider possible mitigation measures, their likely effectiveness and
cost, which can be summarised as:
 25% of European railways were already using sulphur free diesel fuel.
 New vehicles will comply with emission limits and there will be a gradual move
towards electrification and (lower emission) diesel railcars in place of locomotives.
 Selective catalytic reduction technology (SCR) could be fitted to existing fleets. Future
fleets could be fitted with diesel particulate filters. The report noted, however, that
there was very little experience of fitting emissions abatement equipment to rail
vehicles – it might, for example, lead to maximum axle loads being exceeded.
3
EU Directive 2004/26/EC on amendments to the Non-road Mobile Machinery Directive
97/68/EC.
8
 Site specific operational measures (for example, restrictions on the length of time
engines are allowed to idle). There are no standard solutions but where they can be
applied they are likely to be implemented more quickly than technical measures.
 Re-engining older traction units.
Of these options only retrofitting SCR technology gave net benefits in a cost benefit
analysis. Subsequent investigations have shown that in many cases the engines
themselves would need re-engineering to operate with this technology, making it either
prohibitively expensive or not practicable.
The UIC report reached a number of significant conclusions:
 Diesel will have an important role in providing rail services in the future.
 A range of technical options are available for the post-1990 fleet, including SCR.
 Heavily trafficked sections of line are insignificant contributors to atmospheric
pollution. However, the contribution to NO2 concentrations by very busy shunting
yards and to both NO2 and PM10 concentration by busy terminal stations may be
important.
 There were concerns that the high implementation costs of measures to meet
emission reduction requirements were disproportionate to the relevance of rail
transport in the overall emissions picture. This, it was suggested, could lead to a
modal shift from rail to road against European transport policy.
The UIC report was based in large part on work undertaken by AEA Technology and
published in October 2005 as work package 3 of the Rail Diesel Study4. This report listed
out four ‘pollutants of concern’: nitrogen dioxide, ozone, sulphur dioxide and particulate
matter. Of these, ozone is a secondary pollutant produced by a reaction between
nitrogen dioxide, hydrocarbons and sunlight, and is not emitted directly into the
atmosphere. Nevertheless, the highest ozone concentrations tend to occur in urban
areas where the precursors for its formation are most abundant.
Figures were given for the contribution of transport to total emissions in London, for the
other three pollutants of concern:
Pollutant
% contribution
from transport
NOx
71
SO2
23
PM10
51
4
Work package 1 collated information on the existing diesel fleet in Europe. Work package 2
assessed the technical and operational possibilities for diesel exhaust emissions reductions.
Work package 3 assessed whether rail diesel exhaust emissions were significant contributors to
local air quality problems and if so where the hotspots were.
9
Transport emissions in London were analysed by mode:
Pollutant
Road (%)
Rail (%)
Shipping (%)
Airports (%)
NOx
90
3
1
6
SO2
32
14
26
28
PM10
92
4
0
4
The report noted that the relatively high contribution of sulphur dioxide by the railway
was a consequence of the high sulphur fuel in use in the UK.
Although the overall contribution of pollutants by rail in London was found to be small,
this aggregated figure did not reflect the existence of hot-spots where rail activities are
intense (shunting yards, terminal stations etc), and where dilution and dispersion is
restricted. This view was supported by the results of a questionnaire to European rail
operators which suggested that, for those operators which received complaints about
air quality (which included the UK), these typically related to hotspots.
From modelling work, the following estimated emissions per kilometre were
determined:
Activity
NOx (kg/km per year)
PM10(kg/km per year)
Motorway
73,840
2,197
Minor road
2,059
125
Busy diesel rail section
9,480
130
Average diesel rail section
542
10
This table shows that that while NOx emissions from a busy diesel railway exceed those
from a minor road, they are substantially less than from a motorway. For particulates,
emissions from a busy railway are similar to those from a minor road.
However, to predict resulting concentrations of pollutants, a number of factors need to
be taken into account including the physical characteristics of the emitting source and
the meteorological conditions. The paper used emission concentrations for road
derived from the UK Design Manual for Roads and Bridges and predicted these pollutant
concentrations for a location 20 metres from different types of roads and railways:
10
Activity
Predicted NO2
3
concentration (µ/m )
Predicted PM
3
concentration (µ/m )
Motorway
12.8
8.7
Minor road
2.1
1.3
Busy diesel rail section
0.3
0.02
Average diesel rail section
0.05
0.001
In this case even a minor road contributes more pollutant concentration than a busy
diesel railway.
For shunting yards three situations were considered, one of which was for an average
yard in terms of size and activity (0.47km2 and 31,639 hours of operation per year).
Modelling showed that NO2 concentrations at the site boundary could be significant
where activity levels were high but not in themselves high enough to create an
emissions hotspot. PM10 concentrations were predicted to be 1µ which does not
contribute significantly to ambient concentrations.
The report’s authors were unable to model the situation in partially covered stations
where air flows are difficult to predict; therefore the work assumed an open
environment with no restricted air flows. The modelling was based on a 12-platform
terminal station in which diesel trains were left idling for 40% of the day. This could lead
to hotspots for both NO2 and PM10 emissions; concentrations of NO2 outside the station
were found to reach a maximum of 12µ/m3 and PM10 reached a maximum of 3µ/m3.
Overall the modelling showed that emissions from diesel trains idling at stations could
significantly contribute to hotspots but on their own would not result in an exceedance
of air quality limit values.
At the time, the broad overall conclusions were:
 Very busy line sections resulted in insignificant pollutant concentrations.
 Very busy shunting yards gave rise to low level pollutant concentrations.
 Large terminal stations, with high levels of diesel activity, gave rise to significant
emissions contributions but still below limit values.
3.2 Other research
In 2007 ATOC published a report specifically examining carbon dioxide emissions for rail
compared with other transport modes. It noted that although a loaded car would have
lower emissions per passenger than an almost empty train, in general emissions for rail
were significantly lower than for other modes. A modal shift from road to rail would
11
therefore reduce overall UK carbon dioxide emissions. Furthermore, marginal rail traffic
increases have a negligible effect on emissions because they can be absorbed by higher
train load factors.
An RSSB research project published in 2007 considered the future of the diesel engine in
some detail, including the various techniques available to reduce emissions. This
referred back to the UIC rail diesel study, described above, noting that this work was
based on modelling work and that there was a need to better map local air quality
around terminal stations. A difficulty in developing technologies to reduce overall
emissions is that measures taken to reduce NOx emissions increase PM and vice-versa.
Several types of equipment designed to treat exhaust emissions were described
including:
 Diesel oxidation catalysts (carbon dioxide, hydrocarbons and particulate matter)
 Diesel particulate filters (for particulate matter)
 Continuously regenerating trap (carbon dioxide, hydrocarbons and particulate matter)
 Selective catalytic reduction5 (for nitrogen oxides)
 NOx absorber
These methods all impose a significant weight, size and cost penalty, especially for retrofit installations, although it was hoped that future developments will produce lighter
smaller and more efficient equipment.
Operational measures to reduce fuel consumption and emissions were also discussed at
the time. These included reducing the amount of time spent with the engine idling, by,
for example, enforcing shutdowns, using shore supplies and auxiliary power units, and
selectively controlling individual engines. Driving techniques implemented either
through training or by the use of in-cab aids, were also seen as potentially having a
significant effect.
4 UK Case studies
4.1 Ealing and Islington
Some studies have been undertaken across the Great Britain rail network to determine
the levels of pollutant emissions from rail sources. Possibly the most comprehensive
was contained in a report prepared by King’s College London for the boroughs of Ealing
5 The selective catalytic reduction process reduces the NOx molecule into molecular nitrogen and
water vapour. A nitrogen based reagent is used to mix with the waste gases downstream of the
combustion unit before entering a reactor module containing a catalyst. The reagent reacts
selectively with the NOx within a specific temperature range in the presence of the catalyst and
oxygen.
12
and Islington and published in July 2014. The work was done in response to concerns
that diesel trains operating in the London area may be responsible for breaches of the
government’s air quality objectives6 for nitrogen dioxide up to 200m either side of the
line.
Two locations were selected: on the Great Western main line out of Paddington in the
borough of Ealing and on the East Coast Main Line out of King’s Cross in the borough of
Islington. Although electrification is taking place, the majority of trains from Paddington
are still diesel operated and a significant proportion of trains out of King’s Cross use
diesel traction to allow through services access to locations off the electrified network.
These are the only two routes out of London to regularly see High Speed Trains (HSTs), a
design dating from the 1970s although they have since been re-engined. Diesel
operated freight trains also use both lines.
Modelled predictions showed that for the Paddington mainline annual mean
concentrations would exceed those close to nearby arterial roads; the modelled
concentrations were lower in Islington but similar concerns had been expressed. The
report pointed out that although there have been many studies of air pollution from
road traffic sources there is practically no information on pollution caused by trains.
What was available concentrated either on in-train exposure or particulate matter in
underground environments (including some Swiss work which was interested in
emissions from electric trains, mainly metals from wheel and rail abrasion).
Consequently knowledge is very limited on the extent to which diesel trains pollute the
environment.
Similarly, test bed work on locomotive emissions in the USA and in Australia where the
concern related to very large freight trains crossing pristine environments in the
outback, were seen to have very little relevance to passenger trains operating in a
densely populated urban area. The aim of the London project was to improve the
accuracy of modelled predictions for the Paddington mainline, to derive new NOx, NO2,
and PM emissions factors for diesel trains using the two lines, determine the cause of
any measured short-term peaks in NO2 emissions, and differentiate between exhaust
emissions and track, wheel and conductor wear.
Analysis of the monitoring data is a complex exercise because of the need to isolate
railway emissions from other sources of pollutants, especially road traffic. Road traffic
includes a mix of diesel and petrol vehicles which have emission ‘signatures’, but in
practice it is very difficult to distinguish between emissions from diesel trains and diesel
road vehicle engines. The researchers applied a variety of techniques to overcome
these difficulties.
The conclusions were somewhat surprising. At Ealing the annual mean NO2
concentrations were less than those predicted by the modelled data; they were also less
6 See http://uk-air.defra.gov.uk/assets/documents/National_air_quality_objectives.pdf
13
than the air quality objective and EU limit values. No increment in NO2 was found when
measured at a point 600m from the railway. Furthermore, the maximum hourly mean
NO2 concentration was less than the short-term EU limit value concentration of
200µ/m3. Small increments were found in the concentrations of NOx and particulate
matter.
Similar results were found for the Islington site, although in this case the maximum
hourly mean NO2 concentration exceeded the EU short-term limit value during periods
of poor pollutant dispersion in London (when the same effect was noted across many
monitoring sites suggesting that local sources were not responsible).
The authors therefore stated, in summary, that it was difficult to detect a clear pollution
signal from the railways in terms of NO2, NOx, PM and PM metals. It was clear that
diesel trains do not make a large contribution to air quality in London. The authors
noted that the finding had clear implications for local air quality management priorities,
although they did point out that a study alongside a busy railway in a rural environment
would provide a better opportunity to quantify railway emissions.
The reports’ conclusions were summarised in a separate presentation:
 Real world measurements did not support the modelled predictions of NO2
concentrations at 50% greater than the limit value.
 It was difficult to detect a clear signal from diesel trains alongside the tracks.
 It was possible that London’s traffic confounded the analysis but it is clear that diesel
trains were not making a big contribution to local particulate matter and NO2.
 Emissions were re-modelled using emission factors from Hobson and Smith (2001)7
and showed good agreements with measurements.
 Without this measurement study unnecessary large resources could have been
expended to abate pollution emissions for diesel train lines that pass through urban
areas.
The findings of the project also raised the important issue of the use of emissions as
predictor of ambient air pollution. The amendment or introduction of emission
sources needs to be verified against real world measurements before being used in
air quality and policy assessments.
4.2 Edinburgh Waverley
The Sunday Herald8 published a story under the lurid headline Millions at risk from air
pollution at Waverley station on 16 December 2012. Politicians were described as
7 Hobson, M., Smith A., 2001. Rail emission model. AEA Technology, Culham.
8 The Sunday Herald is the Sunday edition of the Glasgow based Herald newspaper.
14
reacting with ‘shock and horror’ to the revelations, demanding urgent action to protect
the 25 million people who use the station annually9.
Behind all this hyperbole lay an air quality monitoring assessment undertaken on behalf
of Network Rail by Ethos Environmental ltd, an environmental consultancy firm. The
concerns that gave rise to the study were primarily about the exposure of Network Rail
employees and their contractors rather than passengers; for this reason it addressed
occupational exposure issues. In fact, Network Rail was already carrying out air
monitoring at the station during the on-going redevelopment project. Waverley station
is unusual in being located in a deep cutting, well below street level, and allowing taxis
to enter the premises under the overall roof for picking up and setting down their
passengers.
The consultants noted the concerns over the carcinogenicity of diesel exhaust emissions
and the lack of workplace exposure limits specifically for exhaust. Consequently they
obtained samples of specific constituents of exhaust from four locations around the
station over a three week period. The analysis for particulate matter, polycyclic
aromatic hydrocarbons and nitrogen oxides showed that concentrations were below
existing occupational exposure limits.
The conclusion was that results were in line with expectations for this type of work
environment, although polycyclic aromatic hydrocarbons (PAH) and nitrogen dioxide
were elevated above the background air quality levels. Even assuming worst case
exposure patterns for employees, the levels were:
 Approximately 2% of HSE guidance for respirable particulate
 0.05% of the German occupational exposure standard for benzo(a)pyrene10, which is a
major carcinogenic component of diesel exhaust and indicative of PAH in general.
The German standard was used in the absence of an equivalent British one.
 Approximately 10% of the median exposure for benzo(a)pyrene obtained in UK
industries with the highest risk of PAH exposure11.
 Less than 10% of informal guidance levels for occupational exposure to NO2.
9 This in itself is misleading. The ORR’s figure for usage in 2012/13 was 18.879 million. This, of
course, is not the same as 18.879 million people, because many individuals will use the station on
multiple occasions. It is reasonable to say that this underestimates ‘station users’ because not all
visitors to the station will be travelling by train, but no figures are published for this number.
10 Benzo(a)pyrene is a polycyclic aromatic hydrocarbon found in coal tar with the chemical
formula C20H12. It is believed to have been responsible for the common occurrence of scrotal
th
cancer among young chimney sweeps in the 18 century.
11 This was based on a 2006 HSE study measuring the personal exposures of over 200 employees
in 25 UK industries with higher than average levels of PAH exposure, including tar distillation,
coke ovens, asphalt, oil refinery, power stations and aluminium smelting.
15
The report was therefore able to state that the monitoring results do not suggest that
that station refurbishment work had had an obvious impact on air quality in general or
employee exposures specifically.
Readers of the Sunday Herald story would not have got that impression, although it did
acknowledge that pollution levels were within legal limits for workers. The newspaper
was much more interested in comparisons with air quality in the surrounding streets
(which were not actually part of the consultant’s remit). Network Rail responded by
pointing out that they were limiting the amount of time trains could run with their
engines idling and were restricting vehicle access to the station. In the longer term
electrification schemes would significantly reduce the number of diesel trains at
Waverley station.
4.3 Paddington
Paddington station has been the subject of a very recent paper, published in September
2015, by Chong, Swanson and Boies, which described an air quality evaluation
undertaken within the enclosed area of the station. The authors note previous air
quality measurements at the station but these were taken in the surrounding area; data
on emissions within the station have previously been extremely limited. The intention
was to compare the indoor air quality with regulated outdoor sites, two of which were
chosen at Marylebone Road (a busy roadside) and North Kensington (an urban area
used for reference purposes). All measurements were carried out in 2012.
It should be borne in mind that, as an enclosed location, Paddington Station is not
subject to current EU emissions regulations and that electrification will eventually
eliminate most diesel operations at the location. Paddington is the seventh busiest
station on the British network, used by 38 million passengers annually, so the overall
current level of potential exposure is high.
Pollutants measured included particulate matter, NOx and SO2. Five sites were used
around the station although the length of time over which measurements were taken
was limited by station security requirements12. Remote and continually attended
equipment was used.
Under current rules trains are allowed to idle at Paddington for a maximum of ten
minutes; this makes up 37.8 train-hours daily, while acceleration activity was calculated
to make up 1.6 train-hours daily. Idling emissions were estimated to be between four
and six times greater than acceleration emissions. A morning peak for emissions was
identified between 0700 and 1000.
The results showed that for particulate matter hourly mean concentrations within the
station exceeded those at both the Marylebone Road and North Kensington sites,
although there was some variation between different monitoring locations within the
12 It is not clear what the specific security concern was.
16
station and different days. The picture for nitrogen dioxide was similar; concentrations
were higher at all the station locations than the North Kensington site but only in some
locations on some days were they higher than Marylebone Road. For Sulphur dioxide all
recorded concentrations within the station were higher than those outside.
In their conclusion the authors state that if the standards applicable to indoor and
ambient locations were applied at Paddington, it is likely that action would be necessary
to achieve compliance. As possible mitigation measures they suggest that trains could
be fitted with diesel particulate filters with catalytic regeneration, and that passenger
waiting areas could be physically isolated using platform screen doors. The difficulties
with filters are referred to in section 3 of this report; platform screen doors are unlikely
to be a practical solution at a station with a broad mix of different types of trains.
In a subsequent summary of this report the authors provided some additional
information about the position of the monitoring equipment which suggests that the
results may have been influenced by other sources of particulates independent from the
railways (see attached poster). One of these was adjacent to the Burger King outlet at
the east end of platform 8; it recorded higher measured data than the two locations at
the western end of the platforms (adjacent to HST power cars) with a peak in the
evening. This was attributed to cooking emissions, corresponding to the busiest times
for the outlet. The highest particulate concentrations were recorded on the Praed
Street ramp, some distance from the platforms, where smokers habitually gather; it
would therefore appear that these more local sources of pollution were significantly
affecting the overall results. Further work is thus needed to ensure that an accurate
picture of emissions at Paddington can be drawn.
4.4 Paddington (CIRAS report)
A report was received by CIRAS, the rail industry’s confidential safety reporting system,
about diesel fumes at terminal stations operated by First Great Western13. The reporter
was concerned that trains were left with their engine running. Although the reporter
did not refer to a specific location, Paddington would be an obvious location where
problems might occur because of the high proportion of diesel trains using the station
and its location below the level of surrounding streets.
In response First Great Western thanked the reporter for bringing the issue to its
attention. It went on to state that ‘established procedures are in place to limit the
effects of fumes and noise emissions at terminating stations. The procedure at
Paddington, for example, is described in the Western Route Sectional Appendix’. The
sectional appendix states that trains must be coupled to the shore supply and shut down
until ten minutes before departure time. Where local instructions do not apply, the
procedures set out relating to ‘idling diesel engines and the control of noise’ should be
applied.
13 CIRAS reference 51433
17
The company also stated that scientific monitoring is undertaken at stations, including
Paddington, Penzance and Bristol Temple Meads.
5 Railway Industry Initiatives
Although the overall contribution of the rail industry to atmospheric pollution in Great
Britain is relatively small, the industry has taken a range of initiatives to minimise the
risk of exposure to the public and staff. These take the form of modifications to
locomotives, ensuring that diesel fumes are minimised in enclosed spaces, and the
complete elimination of diesel operations. The basic legal requirements to ensure
compliance with the Control of Substances Hazardous to Health 2002, together with
some recommendations as to the appropriate action in different circumstances, are set
out in the ORR’s Railway Guidance Document RGD-2014-04 Diesel Engine Exhaust
Emissions in the Railway Sector. The initiatives described below are designed to comply
with this document and other requirements of environmental law as well as creating a
pleasanter environment for passengers, staff and others who live or have business close
to the railway.
5.1 Eliminating Emissions
There are many advantages to electrified railways, of which the opportunity to eliminate
diesel emissions is one, but the capital cost of conversion is high. Nevertheless, there
are a number of major schemes currently either underway or planned on the Great
Britain rail network; collectively these will significantly reduce the industry’s reliance on
diesel traction. Even where electrification will not take place for many years, or could
never be justified, a re-allocation of existing diesel units means that older types can be
withdrawn and scrapped.
Furthermore, developments in battery technology offer the possibility of providing
electrically powered trains on branch lines off the electrified network where traffic
levels do not support the provision of electrification infrastructure. In this way, the
prospect of the elimination of diesel trains from entire regions of the country becomes a
realistic aspiration.
So far a trial has taken place in which an existing EMU was temporarily retrofitted with
Valence Technology lithium iron magnesium phosphate batteries. It was used on the
Harwich branch in Essex in regular passenger service to establish the viability of this
technology. The six week trial was considered a success – to the extent that the project
received a Rail Industry Innovation Award – and Network Rail was quoted as saying: “We
are continuing to rigorously test the IPEMU battery technology at Bombardier's
test facility in Mannheim, Germany, and are working very closely with the DfT and our
partners, looking at plans for safety and implementation”.
18
5.2 Reducing Emissions
5.2.1 Low emission diesel engines
Changes to emission requirements for railway locomotives were mandated by the
European Union Non-road Mobile Machinery Directive which covers all plant and
machinery that does not operate on roads, and uses spark ignition or compression
ignition engines. The original 1998 directive excluded rail vehicles, but these were
covered under a later amendment14. These requirements were transposed into UK
domestic law by the Non-Road Mobile Machinery (Emission of Gaseous and Particulate
Pollutants) Regulations 1999, as amended.
Under this legislation emission limits are progressively tightened for new machinery,
although older equipment may continue to be used. Currently stage 3B emission limits
apply, introduced from January 2012 although the UK has enjoyed a flexibility
arrangement under which some 3A compliant locomotives could continue to be
marketed. A particular difficulty has been that compliant equipment, which could be
accommodated within the British loading gauge, has not been available from
manufacturers. Furthermore, the use of filter and clean-up technology to meet the NOx
and PM stage 3B limits results in increased fuel consumption – with the unintended
consequence of producing more CO2.
To meet the requirements UNIFE (the European Railway Industry Association) set up a
research initiative in 2009. Cleaner engine technologies and a reduction in the total
number of diesel locomotives in use (mainly due to electrification and more efficient
operation) had already reduced NOx and PM emissions in Europe by 35% between 1990
and 2008. As a result of its research work, UNIFE expects that NOx and PM emissions
will fall by a further 35% and 45% respectively by 2020.
5.2.2 Low sulphur fuel
EU Directive 2009/30/EC introduced a requirement for all gas oil marketed for use in
non-road mobile machinery to contain no more than 10 milligrams of sulphur per
kilogram of fuel from 1st January 2011. This applied to a variety of different types of
vehicle, ranging from farm tractors to narrowboats15. Railway vehicles were also
included, although in this case the implementation deadline was deferred to 1st January
2012; therefore all diesel engines on the Great Britain network now use this type of fuel.
The legislation was necessary to ensure the reliable operation of pollutant emission
control systems which were mandated by the Non-road Mobile Machinery Directive (see
above). Without low sulphur fuel these systems would suffer progressive and
14
Directive 2004/26/EC
This is often referred to as ‘red diesel’ and is distinguished from road diesel by the lower rates
of duty applied.
15
19
irreversible damage; it was therefore necessary for the EU to ensure that suppliers were
required to make this type of fuel available in order to achieve the emissions objectives.
5.2.3 Stop-start Technology
Stop-start technology, where the engine is stopped from running when idling, is now
well-established in road vehicles. The objective is to reduce both fuel consumption and
emissions. The same principles can be applied to rail locomotives, and DB Schenker has
undertaken a programme to introduce the technology to 90 of its class 66 engines. This
is potentially particularly significant because, due to the nature of the operations, freight
locomotives tend to spend a disproportionate amount of time not moving (for example,
being recessed in loops or held at signals).
Experimental results showed that the amount of time that the engine was running could
be reduced by approximately one third. For the 90 locomotives that equates to a
reduction of CO2 emissions of about 10%, or 4,500 tonnes. DB Schenker stated that the
technology ‘provides huge opportunities to improve the impact of rail freight…We aspire
to become an eco-pioneer and this project is a key part of that strategy’.
A further example of the use of this technology is on class 185 DMUs used by First
TransPennine Express. When climbing, or needing higher acceleration, they use all three
engines per unit, but at other times one shuts down leaving two operational; this is
particularly advantageous on the steeply graded routes through the Pennines.
5.2.4 Idling engines at stations
In addition to developing stop-start technology, the industry has also identified locations
where limits can be placed on the length of time that engines are allowed to idle.
Traditionally, drivers were often reluctant to shut down engines away from depots
because they could not be confident that they would start again; with modern engines
this is unlikely to be a problem. Consequently a more disciplined approach is possible.
In some locations drivers are instructed to shut down in order to reduce noise nuisance,
for example in residential areas. In enclosed stations it is done in order to reduce
emissions pollution (as well as reduce noise) and train hotel services can be provided by
shore supplies. The instructions at Paddington are set out in the Western Route
Sectional Appendix:
Reduction of noise/smoke emission of HSTs. On arrival at Paddington, HSTs must be
brought to a stand with the driving cab opposite the yellow platform marker, except in
platforms 3, 8 and 10 where additional red markers are provided:Platform 8 - red marker 122 feet from buffer stop.
Where necessary, the train must be coupled to the shore supply and both engines must
be shut down until ten minutes before departure time. If the shore supply is not used, the
engine at the country end must be left running, the engine stop block end must be shut
down and re-started ten minutes before departure time.
20
An alternative approach was taken by Chiltern Railways in 2012. This involved fitting its
fleet of driving van trailers (DVTs) with generators to provide trains with hotel power
while the class 67 locomotive at the other end of the train was shut down. This
improves fuel efficiency, reduces noise and reduces diesel emissions – which can be
especially advantageous at the terminal stations (Marylebone and Birmingham Moor
Street) used by Chiltern services where the DVT could be in the open air but the
locomotive at the enclosed end of the station. According to Chiltern Railways: ‘A class 67
locomotive produces a lot of fumes when running just to provide hotel power, partly
because the core power pack is a 2-stroke engine. These fumes contain high levels of
diesel particulates and smoke that can be seen above the engine, reducing local air
quality and potentially leading to long-term blackening of adjacent structures. The DVT
generator engine is a modern electronically controlled 4-stroke engine that produces
less particulate and smoke, and fewer emissions.’
Chiltern Railways DVT at
Birmingham Moor Street
providing hotel power to the
train. ©Roger Cornfoot CCL
5.3 Mitigating Emissions
Most railway stations are open air environments, so there is no need for ventilation
systems. Even where the platforms are enclosed ventilation is not required where
services are all electric. However, a very small number of stations do require
sophisticated ventilation systems, the most obvious example of which is Birmingham
New Street where the platforms are below street level and, except at the extremities,
are completely enclosed with a relatively low height roof. As part of the recent
rebuilding, Network Rail has installed 98 fans across 12 platforms controlled from a
master control panel and seven main control panels. The system aims to prevent the
build-up of carbon dioxide gases from diesel trains to a value of not more than 666PPM
for any 12-hour period. It also limits CO2 build-up in exceptional cases to 3000PPM for a
maximum of 15 minutes. The ventilation fans are also able to remove fumes in the
event of a fire.
21
6 Conclusion
Although the risk associated with diesel exhaust emissions cannot be ignored, the
research work reviewed in this report suggests that the railway industry does not face a
crisis. The industry is a major user of diesel engines and a significant proportion of trains
are diesel operated; that will continue to be the case for the foreseeable future,
although electrification schemes will reduce the overall proportion and developments in
battery technology might see diesel operation reduced still further.
Nevertheless, the evidence that this may be a cause of harm to the public, passengers
and railway employees is extremely limited. In fact, the indication is that emissions of
harmful substances are significantly less than for major roads even from very busy diesel
railways. This is despite the fact that only a proportion of road vehicles have diesel
engines, and petrol engines produce different substances in their emissions which are
not part of the work considered here.
Where monitoring has been carried out emissions have been found to comply with
occupational limit values and air quality policies. Monitoring work at Paddington, which,
due to its physical location and heavy use by diesel trains, may be an exceptional case,
suggests that emissions standards (if they were applicable) would likely be exceeded,
although questions have been raised over the accuracy of the results obtained.
Therefore further monitoring, providing a more comprehensive and definitive picture of
emissions levels at the station, would be necessary to determine exposure risk in
relation to compliance with legislation. In any case by 2019 the majority of trains using
Paddington station will be electric. It should be stressed that to determine air quality
against EU exposure limits really requires more permanent monitoring equipment than
the ones used in the studies described, to develop more robust trend analysis and
weighting.
This does not mean, however, that mitigation measures are unnecessary; it is known, for
example, that diesel exhaust can exacerbate existing complaints for suffers of asthma
and other respiratory diseases. At the least, an atmosphere heavy with diesel fumes is
unpleasant for passengers, staff and the public. Therefore, the industry has taken steps
to reduce engine idling by, for example, fitting stop-start technology to diesel
locomotives and shore supplies to provide hotel power to passenger trains at stations.
22
7 Bibliography
Abbasi, S., Jansson, A., Sellgren, U. & Olofsson, U., 2013. Particle emissions from rail
traffic: a literature review, s.l.: s.n.
AEA Technology, 2005. Rail Diesel Study Work Package 3: The contribution of rail diesel
exhaust to local air quality, s.l.: s.n.
Association of Train operating Companies, 2007. Baseline energy statement - energy
consumption and carbon dioxide emissions on the railway, s.l.: s.n.
Cancer Research UK, 2014. Diesel exhaust fumes 'definitely' cause cancer - should we be
worried?. s.l.:s.n.
Chong, U., Swanson, J. J. & Boies, A. M., 2015. Air quality evaluation of London
Paddington train station. Environmental Research Letters.
Ethos Environmental Ltd, 2012. Environmental air quality monitoring assessment:
Waverley Station, Edinburgh, s.l.: s.n.
Fuller, G. et al., 2014. Air pollution emissions from diesel trains in London, s.l.: King's
College London.
Garshick, E. et al., 2004. Lung cancer in railroad workers exposed to diesel exhaust.
Environmental Health Perspectives.
Health and Safety Executive, 2012. Control of diesel engine exhaust emissions in the
workplace, third edition, s.l.: s.n.
RSSB, 2007. The future of the diesel engine - research report, s.l.: s.n.
Schenker , M. B. et al., 2003. Diesel exposure and mortality among railway workers:
results of a pilot study. British Journal of Industrial Medicine, Volume 41, pp. 320-327.
UIC CER, 2006. Rail diesel emissions - facts and challenges. s.l.:s.n.
Westminster City Council, 2005. Detailed assessment for sulphur dioxide, s.l.: s.n.
Woskie, S. R. et al., 1988. Estimation of the diesel exhaust exposures of railroad workers:
II. National and historical exposures. American Journal of Industrial Medicine, Volume
13, pp. 395-404.
23
Source Apportionment in London Paddington Station
Uven Chong, Jacob J. Swanson, Adam M. Boies
Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdom
Contact: uc211@cam.ac.uk
RESULTS—PM Measured Data
80
• London Paddington Station is the 8th busiest train
station in Great Britain, serving 30 million
passengers in 2010.1
60
• Non-road mobile machinery PM emissions limits
were lowered 88% in January 2012 from 0.200
g/kWh to 0.025 g/kWh.3
• Fuel sulphur content was lowered from 1000 ppm
to 10 ppm in January 2011.4
• The purpose of this study is to characterise
particle emissions in London Paddington Station
and apportion the sources of emissions.
RESULTS—PM Size Distribution
106
EU 24 Hour Limit for PM10 = 50g/m3
40
Burger King (Location C)
20
Platform 1 (Location A)
Platform 8 (Location B)
0
4
EU 1 Year Limit for PM2.5 = 25g/m3
London Roadside 17-21 Sept. 2012
Mean = 15.5 g/m3 (KCL)
8
Time (hour)
12
• A suite of real time particle characterisation
instruments and gas analysers collected data at 2
locations (A and C).
Table 1: List of equipment used and species measured.
Species
PM0.8 mass
PM number
SO2
NOX
PAH
Metals
Anions
Equipment Used
AM510 + Dorr Oliver cyclone
SMPS and CPC
UV Fluorescence Analyser
Chemiluminescence Analyser
Pump + Quartz Filters
Pump + Cellulose Filters
Pump + PTFE Filters
• The Burger King and Praed Ramp are close to
both food, diesel, and smoking emissions while
the platforms are close to only diesel exhaust.
• Burger King and Praed Ramp PM0.8 results
indicate that EU limits could be exceeded because
PM0.8, which is a subset of PM2.5 and PM10,
already exceeds limits during certain time periods.
3 x 10
2.5
1
Platform 1 (Location A)
0.5
London Roadside Sept. 2011 Hourly Mean = 0.38x105/cm3 (DEFRA)
0
4
8
12
Time (hour)
16
20
• The peak at the end of the day for Burger King PM
number corresponds with the PM mass increase
in Figure 2. This is likely due to increased cooking
for the evening rush hour crowd.
• EC/OC composition results were calculated from a
quartz filter analysis.
• Using the EC/OC data, the contribution of train
diesel emissions to total PM0.8 was estimated.
E
Table 2: List and description of measurement locations.
Location
A
B
C
D
E
Description
Platform 1 (Class 43 locomotives)
Platform 8 (Class 165 multi- unit)
Burger King grilling emissions
Praed Ramp station entrance
Outside by station roadside
Percent of PM0.8 from Diesel Train
60%
Figure 1: Map of measurement locations.
Platform 1 (Location A)
Burger King (Location C)
100
Mobility Diameter (nm)
Figure 5: SMPS results from Monday with and without a catalytic stripper
• The difference between the 2 distributions is the
volatile portion of total PM, which is removed by
the catalytic stripper.
• Using the catalyst and SMPS, EC/OC ratios were
calculated assuming log-normal distributions.
100
Idling
Moving
50
0
0
4
8
12
16
Time (hour)
24
• This model will be inputted into a mixed-box
model to estimate and validate PM values.
Summary
• PM concentrations are higher in the Burger King
and Praed Ramp than the train platforms because
they are closer to more emissions sources
(cooking, smoking, and diesel exhaust).
• A catalytic stripper and SMPS speciation method
was used to further calculate EC/OC ratios in
order to quantify emissions sources of PM.
• Dr Win Watts and Dr David Kittelson for loaning
measurement equipment.
20%
Tuesday
Wednesday
Thursday
Figure 4: Estimated diesel train contribution to PM emissions.
• The UK Engineering and Physical Sciences
Research Council (EPSRC) and the Schiff
Foundation for funding this project.
• Network Rail for granting access to Paddington.
REFERENCES
1. ORR (2010) 2009-10 Station Usage Report & Data. UK Office of Rail Regulation
2. DfT (2009) Britain’s Transport Infrastructure. UK Department for Transport.
3. EU (2004) Directive 2004/26/EC of the European Parliament and of the Council. Official Journal of the
European Union L-146.
4. EU (2009) Directive 2009/30/EC of the European Parliament and of the Council. Official Journal of the
European Union L-140
5. See and Balasubramanian (2008) Atmos. Env., 42, 8852-8862.
6. Ntziachristos, L; Samaras, Z. EMEP/EEA air pollutant emission inventory guidebook—2009: Road
Transport. Technical Report No 9/2009; European Environment Agency, Copenhagen, Denmark, 2010.
24
20
Figure 6: PM emissions estimate from diesel trains on Tuesday May 8 2012.
ACKNOWLEDGEMENTS
40%
0%
10
• A quartz filter based EC/OC speciation method
was used to quantify the PM from food and diesel.
Total EC = ECTRAIN + ECFOOD
Total OC = OCTRAIN + OCFOOD
ECFOOD/OCFOOD=0.195
ECTRAIN/OCTRAIN=3.956
D
Measured EC/Total PM (8.82 - 360.1 nm): 0.478
• A PM emissions model was created with engine
specific emissions factors and train schedules.
Burger King (Location C)
Figure 3: PM hourly mean concentrations averaged over 17-21 Sept. 12.
C
SMPS PM Mass Derivations:
FUTURE WORK—PM Modelling
2
1.5
RESULTS—EC/OC Speciation
A
102
101
• PM number concentrations are also higher in the
Burger King than in Platform 1 on average.
B
With CS
103
Log-normal fit derived EC/Total PM (1 – 800 nm): 0.698
Figure 2: PM mass hourly mean compared to EU regulations.
Particle Concentration (#/cm3)
• Personal aerosol monitors and pumps with filters
were placed in the same 5 locations (A, B, C, D,
and E) and data was collected for 6-8 hours daily.
104
16
5
METHODOLOGY
Total PM
105
Praed Ramp (Location D)
dN/dLogdp (cm-3)
• 70% of train journeys in Paddington are diesel. It
is the terminus for the Great Western Main Line
(the UK’s longest non-electrified train line).2
PM0.8 (g/m3)
• Enclosed train stations with diesel-powered trains
are a health risk to passengers and workers.
Diesel PM (grams/hour)
INTRODUCTION