Measuring black carbon levels on
journeys to Great Ormond St Hospital
July 2015
1.0 SUMMARY
1.1 Aims
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To be able to give patients – in particular those with respiratory conditions – advice on
which routes and modes of transport are likely to be the least / most polluted.
This was done by monitoring black carbon levels on journeys from three stations (Waterloo,
Kings Cross and Euston) using different forms of transport (walking, taxi, tube and bus).
The monitors measured levels of black carbon in the air (ambient pollution), not the amount
inhaled. It should be noted that more black carbon may be inhaled when a person is
breathing harder and deeper, if they are walking quickly for example. However the
equipment was not able to measure the amount inhaled.
This research was conducted by Cool World Consulting, with the support of NIHR GSTFT/KCL
Biomedical Research Centre, as part of the Cleaner Air for Great Ormond Street Hospital project. For
more information on the monitoring, please see section 3.1 at the end of this report.
1.2 Headline Findings
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Walking was nearly always the least polluted mode of transport, in terms of average and
total levels of black carbon.
o There was mostly true, but there were exceptions to this rule. For example, between
Waterloo and the hospital, there is a quick and direct bus route. There is no quiet
walking route (you have to go over the bridge which has a lot of traffic), and it takes
about twice as long to walk as it does to take the bus, which means more time
inhaling pollution from traffic. This is probably why total levels of black carbon were
shown to be lower for a journey on the bus than walking for Waterloo station.
Quieter walking routes on back streets tended to have lower levels of black carbon
compared to taking busier routes with more vehicles.
The bottom deck of the bus tended to have lower levels than the top deck of the bus.
The biggest variation in the results, in terms of levels of pollution for each mode of
transport, was for taxis. Taxi drivers tended to choose different routes between the stations
and hospital, and some routes were more polluted than others. Also, different routes took
different amounts of time. Both of these variations (routes chosen and time taken) can
cause significant variations in the total levels of carbon. For example, from one station, one
taxi had one of the lowest levels of black carbon out of all of the journeys, and another taxi
had the highest levels of all the journeys. The taxi with the high levels of pollution had
double the average pollution levels of the other taxi journey (most likely because he took a
route with more congestion), and it took longer (nearly twice as long), leading to total levels
that were 3.5 times higher than the other taxi.
Exhaust fumes are not the only source of pollution. On one quieter route between Kings
Cross and GOSH, black carbon levels increased at a certain point on a quiet route, most likely
due to some construction work that was taking place on that street.
1.3 Highest levels recorded
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The highest levels of black carbon at any one time were recorded in Euston station taxi rank
(187.2 µg/m3). The taxi rank is underground and was full of taxis with their engines running,
waiting to pick up passengers.
Levels of black carbon were also very high underground when taking the tube (67.8 µg/m3).
1.4 Lowest levels
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The lowest levels were recorded in squares and pedestrianised streets (<1 µg/m3) on the
walking routes.
2.0 Results by station
2.1 Kings Cross – Average and total (cumulative) levels of black carbon
The results for the journeys between Kings Cross and GOSH are shown in the table below, and are illustrated on the graph on the next page.
Total (µg/m3)
Journey time
(mins)
Average (µg/m3)
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BUS WALK TAXI (GOSH
WALK - BUS - TOP BOTTOM
TAXI (KINGS X
QUIET
TO KINGS X)
BUSY
DECK
DECK
TO GOSH)
TUBE
74.8
75.1
196.9
222.9
253.3
263.5
369.1
18
4.16
13
5.78
23
8.56
21
10.61
32
7.35
22
11.98
23
16.05
The quiet walking route had the lowest average and total levels of black carbon. The quiet route took a more direct, but more complicated route
involving lots of backstreets and turns. This route was shorter than the busier walking route, which took the main road that the buses use. As a
result, the quieter route had lower average levels (because it look less busy roads), and lower total levels (because it was shorter).
The tube had the highest average and overall black carbon levels. On that journey, levels rose sharply from 2µg/m3 at Kings Cross Station to 59.5
µg/m3 underground, then back down to 0.8µg/m3 at Russell Square. Total levels were around five times higher than for walking. And around 50%
greater than the total levels from taking the bus.
Taxi was sometimes, but not always the quickest way to get to the station. One taxi journey was the fastest of all journeys (13 minutes), but
another was the third longest (22 minutes). This may have been down to the time it took to call / hail a taxi.
As with the walking, the route chosen also had a big impact on the taxi journey results. One taxi took a quick and quiet route, resulting in total
levels that were almost as low as the walking route. He also had his window wide open. Another taxi took a longer and busier route, and had levels
that were 5.5 times higher than the quicker taxi. His window was only open a crack, and he was in more traffic jams, which result in more pollution.
The bus journey times differed, because in one direction the bus route is more direct than the other.
The average levels on the top deck of one bus were shown to be higher than the bottom deck of another bus.
Cumulative black carbon levels - Kings X
400
350
Tube
Black carbon (µg/m3)
300
Taxi 1
250
Bus - bottom
200
Bus - top
150
Walk - busy
100
Taxi 2
50
Walk - quiet
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Minutes
Figure 1: Cumulative black carbon levels – Kings Cross to GOSH
Figure 2: Map of black carbon levels on routes between Kings Cross to GOSH for each mode of transport
2.2 Euston – Average and total (cumulative) levels of black carbon
The results for the journeys between Euston and GOSH are shown in the table below, and are illustrated on the graph on the next page.
Total (µg/m3)
Time (mins)
Average (µg/m3)
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BUS
BUS WALK WALK WALK BOTTOM TOP
BUSY
QUIET
BUSY
TAXI 1
TAXI 2
83.80
107.40
111.60
127.70
129.50
500.63
921.90
14.00
16.00
18.00
20.00
17.00
11.00
14.00
5.99
6.71
6.20
6.34
7.62
45.51
65.85
The total levels of black carbon on the journey using taxi 2 were almost double the levels for taxi 1. This is likely to be because taxi 2 was taken from
Euston station taxi rank, which is underground and was full of taxis with their engines running. The Euston station taxi rank had the highest levels of
black carbon at any one minute on any journey – around three times higher than the highest levels recorded on the underground.
The highest total and average levels were recorded in the taxis. Total levels for taxi 2 were nearly ten times higher than on the bottom deck of the
bus.
Average levels for the walking routes were higher from Euston than from Kings Cross, even though it is a shorter journey. This is likely to be because
the most direct walking route from Euston was a main road used by many buses, whereas the most direct walking route from King’s Cross is much
quieter.
Contrary to the findings of other studies (such as Healthy Air Campaign, 2014i), average and total levels on the bus journeys were lower than for the
walking journeys.
As with the King’s Cross journeys, the average levels on the top deck of the bus were higher than for the bottom deck of the bus.
There was not much difference between the levels of pollution on the quieter and busier walking routes, because the quieter route was also quite
congested.
Cumulative black carbon levels - Euston
1000
900
800
Black carbon (µg/m3)
700
Taxi 2
600
Taxi 1
500
Walk - quiet
Walk - busy
400
Bus
300
Bus - bottom
200
100
0
1
2
3
4
5
6
7
8
9
10
11
Minutes
Figure 3: Cumulative black carbon levels – between Euston and GOSH
12
13
14
15
16
17
18
19
20
Figure 4: Map of black carbon levels on routes between Euston and GOSH for each mode of transport
2.3 Waterloo – average and total (cumulative) levels of black carbon
Total (µg/m3)
Time (mins)
Average (µg/m3)
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WALK WALK WALK BUS BUS QUIET
BUSY
TAXI 1
BUSY
BOTTOM
TOP
TUBE
TAXI 2
144.2
169.1
173
208
214.8
397
792.8
810.3
35
32
20
33
28
28
23
32
4.12
5.28
8.65
6.3
7.67
14.18
34.47
25.32
The lowest average and total levels were recorded on the quiet walking route.
The findings are much the same as for the other stations: the tube had the highest average levels; the taxi that chose the congested route had the
highest total levels; the bottom of the bus had lower levels compared to the top deck; the walking routes had low levels; and the quiet walking
route had lower levels than the busier walking route.
Again, there is a big difference between the taxi results. Taxi 1 took a quicker route, which had less traffic and lower average pollution levels. Taxi 2
took a longer, more congested route and had total levels that were nearly five times more than taxi 1.
Cumulative black carbon levels - Waterloo
900
800
taxi 2
700
Black carbon (µg/m3)
tube
600
bus top
500
Walk - busy 1
taxi 1
400
Walk - quiet 2
300
Walk - quiet 1
200
100
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Minutes
Figure 5: Cumulative black carbon levels – between Waterloo and GOSH
Figure 6: Map of black carbon levels on routes between Waterloo and GOSH for each mode of transport
3.0 Further information on the monitoring
3.1 Monitoring
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The air quality monitors recorded readings of black carbon levels every minute. The black
carbon is measured as microgrammes of black carbon per cubic metre (µg/m3).
GPS machines were used alongside the black carbon monitors, so that the levels of black
carbon could be mapped along the journey. The GPS did not work on the underground.
The monitors and GPS machines were switched on inside the hospital / station, and switched
off when the destination was reached.
3. 2 Modes of transport
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For walking routes, the pollution levels on the most direct routes (which often involved
taking busy roads) were compared to the pollution levels on quieter routes (which involved
back streets).
For taxi journeys, the taxi drivers were not told to take a specific route, because this would
not normally happen when a patient takes a taxi to / from the hospital. Taxi drivers tended
to choose different routes, and there are therefore some significant differences between the
taxi journey results.
For bus journeys, the most direct routes were taken from the stations to the bus stops on
Southampton Row. Some journeys were monitored on the top deck of the bus, and others
on the bottom deck.
Tube journeys were monitored from Kings Cross station and Waterloo station. The tube was
not monitored from Euston station because it is unlikely anyone would choose that route.
The journey is longer by tube than all other modes of transport, including walking. And there
is no direct tube line, so passengers would have to change lines, and the journey would
involve steps (making it difficult for buggies and wheelchairs).
This research was conducted by Cool World Consulting, with the support of NIHR GSTFT/KCL
Biomedical Research Centre, as part of the Cleaner Air for Great Ormond Street Hospital project.
This project was funded by the Mayor’s Air Quality Programme. Find out more about this research
by visiting www.coolworldconsulting.co.uk.
i
Healthy Air Campaign, 2014. http://healthyair.org.uk/healthiest-transport-option-video/