Differences in Cyclists and Car Drivers Exposure to Air Pollution
from Traffic in the City of Copenhagen
Jette Rank (1), Jens Folke (2) and Per Homann Jespersen (1)
(1) University of Roskilde, Department of Environment, Technology and Social
Studies, P.O Box 260, DK-4000 Roskilde, Denmark.
(2) MFG-Environmental Research Group, Østergade 30, DK-3250 Gilleleje,
Corresponding author to whom the proofs should be sent:
Jette Rank, Department of Environment, Technology and Social Studies, 11.2,
Roskilde University, P.O Box 260, DK-4000 Roskilde, Denmark.
E-mail email@example.com, Phone +45 4674 2071, Fax +45 4674 3041
It has frequently been claimed that cycling in heavy traffic was unhealthy, more so
than car driving. To test this hypothesis teams of two cyclists and two car drivers in
two cars were equipped with personal air samplers while driving for four hours on
two different days in the morning traffic of Copenhagen. The air sample charcoal
tubes were analysed for content of benzene, toluene, ethylbenzene and xylenes
(BTEX) and the air filters for particles (total dust). The concentrations of particles and
BTEX in the cabin of the cars were 2-4 times greater than in the breathing zone of
cyclists, the greatest difference being for BTEX. So, even taking an increased
respiration rate of cyclists into consideration, car drivers seem to be more exposed to
airborne pollution than cyclists.
Key words: traffic, air pollution, benzene exposure, car driver, cyclist.
In Denmark, as in most other countries, the number of cars is increasing and so is the
concern about the impact on human health caused by traffic related emissions.
Obviously, it is important to obtain knowledge of the amount of the most dangerous
air pollutants from the car exhaust, and already a lot of effort has gone into
monitoring the concentrations of these chemicals in urban air (Raaschou-Nielsen et
al., 1996; Jo & Choi 1996; Duffy & Nelson 1997; Fromme et al., 1997).
Exposure to the pollutants affects different kinds of road users, and
among these car drivers are of special interest, because many people spend several
hours every day inside an automobile. Volatile organic compounds have been
measured in car cabins and it was found that the inside-car concentrations were much
higher than the outdoor concentrations (Weisel et al., 1992) and concentrations in
buses (Jo & Choi, 1996) and also higher than what was found in a subway train
(Fromme et al., 1997/98).
Personal air sampling has been used in a Dutch study, where CO, NO2, benzene,
toluene, xylenes and PAH were sampled on persons either driving a car or a bicycle
(Wijnen et al., 1995). The study took place in Amsterdam, where cyclists and car
drivers drove the same routes through the city. The measurements showed that the
exposure levels were greater for the car drivers than for the cyclists. Moreover, a
Danish study using personal air sampling of children’s exposure to volatile organic
compounds, showed a highly significant correlation between exposure to benzene and
time spent in a car (Raaschou-Nielsen et al., 1997).
The main purpose of the present study was to compare the exposure levels of
four aromatic hydrocarbons, benzene, toluene, ethylbenzene and xylenes (BTEX) and
particulate matter for car drivers and cyclists, respectively, while driving the same
route in the traffic of Copenhagen.
A field pilot study was conducted using cyclists and car drivers equipped with two air
sampling pumps: one with a charcoal test tube and one with an air filter. Two teams of
two cyclists and two car drivers drove a slow 7.6 km. route (< 30 km/h average speed)
through the inner Copenhagen for four hours in the morning hours: 7.40 - 9.40 and
10.00 - 12.00, at two dates in the summer 1998, 18 June and 3 August. Both cars used
were typical B-class vehicles from the 90ies (VW Vento and Fiat Brava). None of
them used the air vent recirculation option during the experiment.
Meteorological data (Table 1) were obtained from the measuring station situated at
Kastrup Airport in Copenhagen.
All sampling equipment came from the Danish Technological Institute. The air
sampling pumps were adjusted to a flow of 1.9 litres per minute immediately before
the start of the experiment. The tubes and the filters were placed close to the breathing
zone of the car drivers and the cyclists. For the cyclists the position was on the chest
and in the cars they were positioned at the top of the back on the drivers seat.
Vapours of benzene, toluene, ethylbenzene and xylenes (BTEX) were collected on a
gas sampling charcoal tube at a flow of 1.9 litre per minute. The detection limit of the
method was 0.05 – 0.1 µg/compound. BTEX were analysed in a gas
chromatographic/mass spectrometric method, using selected ion monitoring. Total
particulate matter was analysed gravimetrically after sampling on a membrane filter at
a flow rate of 1.9 litre per minute. The filter used was Millipore Celluloseacetate, 37
mm in diameter and 0.8µm pore size. The detection limit for total dust was 10
Data were analysed in a three-way ANOVA design without interaction terms. The
dependent variables were as follows: concentrations of benzene, concentrations of
toluene, concentrations of ethylbenzene and xylenes, concentrations of total
hydrocarbon and concentrations of particles (total dust). The independent variables
were: date of sampling (two levels), mode of transport (two levels) and car mark (two
levels nested in mode of transport).
Table 1 shows the meteorological data for the two sampling days. The temperature
and the air pressure were very similar for the two days. The most significant
difference was seen for the wind velocity being highest at the sampling day in June.
The samplings were carried out both in the morning rush hour and late morning. Data,
describing the sampling conditions, are shown in Table 2. The average speed for the
cars was low during the morning rush hours (17.8±2.3 km/h) and very similar to the
speed for the bicycles (14.6±0.3 km/h). However, in the late morning the cars are
driving faster, and the difference in speed between the cars (24.1±2.3 km/h) and the
bicycles (15.4±0.3 km/h) was more significant.
The results of BTEX and particle measurements can be seen in Table 3. The benzene
concentrations were in the range 11.0-17.5 µg/m3 in the cabins and 4.5-5.6 µg/m3 in
the breathing zone of the cyclists, giving about three times higher exposure for the car
drivers than the cyclists. The air concentrations of toluene and ethylbenzene/xylenes
are about four times higher than the benzene concentrations, and the exposure of the
car drivers for these chemicals are also about three times higher than the exposure of
the cyclists. The same pattern can be seen for the particulate matter, although the
ratio between the exposure of drivers and cyclists is only about a factor of two. The
results from 18 June showed a significant difference in the concentrations of all
pollutants between the two cars. The VW had the vent in a higher position on this day,
which may explain the lower concentrations measured inside this car due to more
Table 4 shows the results from the analysis of variance (ANOVA). In all of the tests,
the concentrations were significantly dependent of the mode of transport, whereas no
significant differences could be observed between the two car marks. Another
significant result was that the level of particulate matter was higher on the first
sampling day (P = 0.009), while none of the hydrocarbons showed dependency on the
sampling date. The explanation for this phenomenon could be that on this day in June,
where the wind velocity was 8.5 m/s, the dust in the streets could have been whirled
around more than on the day in August, where the velocity of the wind was only 1-3
m/s (Table 1).
Road users are exposed to many hazardous chemicals, which are representatives for
traffic related air pollution. The most important parameters are BTEXs, PAHs, NOx,
CO, 1,3-butadiene and particles (Winjen et al., 1998), and among these we have
measured BTEX and particulate matter using personal air samplers.
Exposure to particulate air pollution can cause severe health problems. McConnell et
al. (McConnell et al., 1994) observed a positive association between PM10 and
bronchitis in children with a history of asthma in southern California, and recently
Pope III et al (Pope III et al., 1999) showed a dose-relationship between PM10
concentrations and daily mortality in Utah.
Among the BTEX compounds benzene is considered to be the most hazardous.
Benzene is a well-known carcinogen (WHO, 1993) and among all the volatile organic
compounds related to traffic, it is the chemical of most health concern (Guerra et al.,
1995; Fromme, 1995).
We consider BTEX a good indicator for exhaust gases from gasoline engines, while
particles originate from various combustion sources and therefore indicate a more
unspecific pollution. Further, the ratio of exposure between car drivers and cyclists
was found to be about two times higher for BTEX compared to particulate matter
(Table 4). Therefore, we consider the benzene results of the present study to be of the
greatest significance, and these are thus discussed in further detail in the following.
In a comprehensive review by Wijnen and Zee (1998) many studies of volatile
organic compounds are reported, which showed higher in-vehicle concentrations than
were found in the ambient air. In-car concentrations of benzene in three American
cities were in the range 10-17 µg/m3. This is very close to what was found in our
study, while in-vehicle concentrations in Amsterdam were much higher with a
variation of 43-74 µg/m3.
In another review of Gennart et al. (1994), results from studies of in-vehicle benzene
concentrations showed much higher concentrations than this study. Thus, driving in
dense traffic in Sweden showed 100-200 µg/m3, and when queuing, the
concentrations reached 200-400 µg/m3. Higher concentrations of benzene within a car
compared to the ambient air were found in a study by Weisel et al. (1992), who
estimated that the difference was allowed up to 50 times higher inside the cabin than
outside. The great variations of benzene concentrations in the above mentioned
studies could be due to many factors, the most important being the concentration of
benzene in gasoline. When this study was carried out the benzene concentration of
gasoline could be up to 5 mg/l, while the limit value shortly after the study was
lowered to 1mg/l to comply with new EU regulations. Other factors may also
influence the in-vehicle benzene concentrations. Duffy and Nelson (1997) showed in
study from Sydney that the age of the cars is of great importance. They found in-car
concentrations of old cars (pre 1986 without catalyst equipment) to be twice as high
as in newer cars. Rømmel et al. (1999) found that the BTEX concentrations in the
streets of Munich decreased significantly during the years 1993 to 1997, indicating
that replacement of old cars may influence the concentrations of the volatile
The study by Winjen et al. (1995) showed a respiratory average of 2.3 times higher
for the cyclists compared with the car drivers. By using this factor we have calculated
that car drivers still get twice as much benzene (0.2 µg/min) into the lungs than bikers
(0.1 µg/min). It could be argued that car drivers are exposed to a lesser degree due to
a higher speed. However, our results show that during the rush hours the speed of the
car drivers is very similar to the speed of the cyclists. Moreover, if we consider the
children transported on the back of a bicycle they will inhale lesser pollutants than
inside a car, because they as passive passengers exhale the same amount of air in the
Concern for small children as road users is important, taking into consideration that
benzene can cause leukaemia, and that leukaemia can be correlated to car ownership
(Wolf, 1992). Further, a study by Savitz and Feingold (1989) has shown that
childhood cancer can be correlated to trafic density and later Nordlinder and Järvholm
(1997) found that car density could be correlated to acute myeloid leukemia in
children and young adults.
Among the pollutants analysed in the present study, benzene is the only
compound that may cause adverse effects in the measured concentrations. WHO
(1995) has established a life span risk of cancer during 70 years of one cancer
observation per million people at 0.13 – 0.23 µg/m3. The actual measurements are 5 –
14 µg/m3, i.e. at least 40 to 50 times above this concentration.
On the basis of this study we can conclude that cyclists in the City of Copenhagen are
exposed to lower concentrations of traffic related pollutants than car drivers. Further,
it can be concluded that car drivers experience 3-4 times higher BTEX concentrations
and around two times higher exposure of particles than bikers. The study also
indicates that children may experience a better atmosphere on the back of a bicycle
than inside a car.
The authors wish to thank Lykke Enøe and Anne-Grethe Winding, who assisted the
experimental planning and sampling, and Henrik Demant, Jesper K. Hansen, Dennis
Madsen and Jacob Turman, who participated in the field study. The Danish Ministry
of Transport funded the study.
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Table 1. Meteorological data from the two sampling days.
18 June 3 August
Wind velocity (10 m’s height) m/s 8.5 1-3
Wind direction W NW – E
Temperature °C 13,3 14
Air pressure Pa 1017 1024
Humidity % 61 90 ® 70
Bicycling and driving data for the two sampling days
Date Period Time Rounds Speed
Time Rounds Speed
min (7.6 km) km/h
min (7.6 km) km/h
18 June Rush hour VW 120 4 15.2 Cyclist 1
120 4 15.2 Fiat
114 4 16.0 Cyclist 2 120
Late morning VW 120 6 22.8
Cyclist 1 113 4 16.1
Fiat 105 6 26.1
Cyclist 2 113 4 16.1
3 August Rush Hour VW 115 5 19.8 Cyclist 1
130 4 14.0 Fiat
113 5 20.2 Cyclist 2 130
Late morning VW 120 6 22.8
Cyclist 1 125 4 14.6
Fiat 110 6 24.9
Cyclist 2 125 4 14..6
Rush hour, average 17.8±2.3
14.6±0.3 Late morning, average
Concentrations of BTEX and particles (total dust) sampled on two
different days in the city of Copenhagen, 1998.
Pollutant Date Car µg/m3
Benzene 18 June VW 11.0 Bicycle 1
Bicycle 2 5.4
3 August VW 15.5 Bicycle 1
Bicycle 2 4.5
Toluene 18 June VW 41.2 Bicycle 1
Bicycle 2 19.4
3 August VW 77.0 Bicycle 1
Bicycle 2 19.6
ethylbenzene 18 June VW 42.8 Bicycle 1
and xylenes Fiat 72.6
Bicycle 2 18.7
3 August VW 73.9 Bicycle 1
Bicycle 2 20.4
Particles, 18 June VW 88 Bicycle 1
total dust Fiat 120
Bicycle 2 68
3 August VW 45 Bicycle 1
Bicycle 2 21
Results from ANOVA analysis
Car Bicycle Standard error P
µg/m3 µg/m3 of estimates, µg/m3
Benzene 14.4 5.2 1.1
Toluene 69 21 6
0.004 3.4 Ethylbenzene 67
18 4 0.001 3.7 and xylenes
Hydrocarbons 215 58 9
0.0002 3.7 Particles (total dust) 75 44
4 0.007 1.7