Preliminary measurements of aromatic VOCs in public transportation modes in Guangzhou, China

Article (PDF Available)inEnvironment International 29(4):429-35 · August 2003with95 Reads
DOI: 10.1016/S0160-4120(02)00189-7 · Source: PubMed
Abstract
This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou, China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/p-xylene and o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the benzene measured, the mean exposure level in taxis (33.6 microg/m(3)) was the highest and was followed by air-conditioned buses (13.5 microg/m(3)) and non-air-conditioned buses (11.3 microg/m(3)). The exposure level in the subway (7.6 microg/m(3)) is clearly lower than that in roadway transports. The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.

Figures

Preliminary measurements of aromatic VOCs in public
transportation modes in Guangzhou, China
L.Y. Chan
a,
*
, W.L. Lau
a
, X.M. Wang
b
, J.H. Tang
b
a
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China
b
State Key Laboratory of Organic Geochemistry, The Chinese Academy of Sciences, Wushan, Guangzhou, China
Received 18 August 2002
Abstract
This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou,
China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and
air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/p-xylene and
o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/
MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the
benzene measured, the mean exposure level in taxis (33.6 Ag/m
3
) was the highest and was followed by air-conditioned buses (13.5 Ag/m
3
)
and non-air-conditioned buses (11.3 Ag/m
3
). The exposure level in the subway (7.6 Ag/m
3
) is clearly lower than that in roadway transports.
The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to
each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be
similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the
VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant
change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving
traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.
D 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Public transportation modes; VOC; Benzene; Traffic; Exposure
1. Introduction
Recently, there was an increasing concern of commuter
exposure to volatile organic compounds (VOCs) in daily
commuting trips. The commuting microenvironment has
widely been recognized as an important sector that can
cause elevated personal exposure to many VOCs. Exposure
to VOCs, particularly those classified by the United States
Environmental Protection Agen cy (USEPA) as known or
suspected carcinogens, can cause adverse health effects
because of their toxicity and potential health hazards. For
instance, benzene is a carcinogenic compound and is closely
linked to the induction of leukemia. The presence of some
VOCs in the a mbient air is also associated with the
deterioration of air quality due to the formation of photo-
chemical smog and tropospheric ozone.
In the past, most of the published in-vehicle air pollution
studies tended to focus on the exposure of private vehicle
user. Only few oversea studies examined the exposure level
in public transportation modes. Duffy and Nelson (1997)
investigated the benzene level in the cabin of moving motor
vehicles and buses in Sydney, Australia. The results
revealed that the concentration measured inside buses were
about 50% of the in-vehicle average determined for newer
catalyst-equipped cars. In Taegu, Korea, Jo and Yu (2001)
reported that taxi drivers were exposed to higher aromatic
compound levels than bus drivers during their daily work
time. The concentration difference might be due to differ-
ences in vehicle height, vehicle cabin volume, smoking
status and driving parameters. In Paris, France, Dor et al.
(1995) stated that the mono-aromatic hydrocarbons (MAHs)
inside vehicles come essentially from the exhaust of neigh-
bouring vehicles, which penetrate the cabin either naturally
0160-4120/02/$ - see front matter D 2002 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0160-4120(02)00189-7
* Corresponding author. Tel.: +852-2766-6026; fax: +852-2334-6389.
E-mail address: celychan@polyu.edu.hk (L.Y. Chan).
www.elsevier.com/locate/envint
Environment International 29 (2003) 429 435
or by ventilation. And the exposure level of MAHs inside
car is two to three times greater than that recorded with other
means of transportation, including subway and bus.
Guangzhou is a fast growing and economically developed
city in South China. The city has an area of about 7500 km
2
and a population of about 7.0 million. Its overall economic
power is the third among all China’s cities and just after
Shanghai and Beijing. In year 2000, the gross domestic
product (GDP) value of Guangzhou reached 238.3 billion
Yuan. The average annual growth rates of the total GDP
value as well as the GDP value per capita increased more
than 20% over the last decade (GZSB, 1999, 2001). How-
ever, as a consequence of rapid development and urban-
ization in Guangzhou, traffic-related air pollution was found
to be one of the major environmental p roblems. Recent
studies had reported that traffic-related pollutants such as
PM
2.5
,PM
10
, CO and NO
x
in the urban sites of Guangzhou
frequently exceeded the Chinese National Air Quality Stand-
ard (We i et al., 1999 ; Zhang et al., 1 999) .Therewere
1,340,548 licensed mot or vehicles and 5020 km of public
road in the whole territory in the end of 2000. Similar to most
metropolitan cities in Asia, public transportation modes are
greatly utilized and is a major component in the composition
of daily commuting trips in Guangzhou (Deng et al., 2000).
Everyday, more than 5 million passenger journeys are made
on the public transportation system. The number of public
transportation trips has increased sharply and continuously
since the early 1990s. Most commuters are required to spend
12 h in their daily commutes. As there is limited informa-
tion on in-vehicle VOC exposure data in the study area, the
primary aim of this study is to compare the exposure levels
of benzene, toluene, ethylbenzene, m/p-xylene and o-xylene
in four popular publi c transportation modes while commut-
ing in the urban area of Guangzhou. The target compounds
are strongly associated with vehicle use and are commonly
known as vehicle emission markers (Chan et al., 1991).
2. Field study design
Four po pular public tra nspor tat ion modes, which are
subway, taxis, non-air-conditioned buses and air-conditioned
buses, were selected in this study f or aromatic VOCs
measurement. These four commuting modes together served
more than 85% of the total public transportation journeys in
year 2000. Buses are the cheapest and the most abundant
mode of transport. There are about 300 bus routes in the
urban area of Guangzhou. They provide convenient access to
every corner of the city. Most of the buses are diesel fuelled.
In air-conditioned buses, the wi ndows are closed and air
conditioning system is used throughout the year. Taxis
provide a supplementary service to other major transporta-
tion modes. They operate throughout Guangzhou, 24 h/day.
In the year 2000, there were about 15,620 taxis. Nearly all of
them are gasoline fuelled. Air conditioning systems are
installed in all taxis. The ventilation condition of taxis was
fixed with windows closed, air-conditioning on and fresh air
vent closed in this study. Thi s was the most typical and
common setting in Guangzhou taxis during the sampling
period. The subway system is an urban underground railway
network traversing the inner city. Line 1 is 18.5 km in length
and connects the Guangzhou East Station and the south-
eastern part of the city while Line 2 is under construction and
not yet finished. Underground electrified trains provide fast
and safe commutes to the citizens. Centralized air condition-
ing system is adopted in trains.
As there is no co-located route for all selected roadway
transports, two independent bus-service routes, Route 1
Table 1
Features of the sampling routes
Transport Route Average journey
time (min)
Average vehicle
speed (km/h)
Characteristics of route
(1) Subway (Line 1)
Guangzhou East
Station Xilang
30 37.0 Runs within the inner
Guangzhou City. Running
mostly on its own 18.5 km
underground track.
(2) Non-A/C bus
a
(Route 1)
Guangzhou
East Station
Youth Park
55 15.6 A 14.3-km main road with six
to eight driving lanes.
Crosses busy commercial areas,
shopping districts and residential areas.
Heavy traffic flow, stop-and-go traffic
and many parts of the route are
in street canyon configuration.
(3) A/C bus
b
(Route 2)
Guangzhou East
Station Jichunlu
51 16.1 A 13.7-km main road with
six to eight driving lanes.
The features of this route
are similar to Route 1.
(4) Taxi (Route 1 or 2) 32 or 31 26.8 or 26.5 Same as above
a
Non-A/C bus = non-air-conditioned bus.
b
A/C bus = air-conditioned bus.
L.Y. Chan et al. / Environment International 29 (2003) 429–435430
(14.3 km) and Route 2 (13.7 km), both connecting the
eastern and western parts of the city were selected for non-
air-conditioned bus and air-conditioned bus measurements,
respectively. While taxis trips were traversed on Route 1 on
Monday, Wednesday and Friday and on Route 2 on Tues-
day and Thursday. The features of the sampling routes are
summarized in Table 1 and the location of the routes is
shown in Fig. 1. These two routes are located close to each
other and are similar in length, t raffic density, street
configuration and traffic composition. Hence, they can
provide a good comparison among different roadway trans-
ports. The selected routes are six to eight lanes (dual
direction) on average and traverse busy central commercial
areas, shopping districts and residential areas. Adding to
that, high traffic density, low vehicle speed and stop-and-go
traffic were frequently observed on these routes. However,
traffic congestion was only occasionally found durin g the
sampling period. The air samples in the subway were
collected on Line 1, which is closed to the routes of
roadway transport.
In this preliminary study, microenvironmental monitor-
ing was performed intensively in a five-consecutive day
period (Monday through Friday) in May 2001. During the
sampling period, a total of 40 VOC samples were success-
fully coll ected and analyzed. On each sampling day, the
VOC samples in all selected commuting modes were
collected in both afternoon non-rush hours (14:00 16:30)
and evening rush hours (17:00 19:30). All the VOC
samples were collected at respiratory level of the passen-
gers. With an aim to have a better understanding of the real
VOC exposure level of the public transport users, all the air
samples were collected during normal service of the trans-
port. Our staff travelled as passengers during sampling. No
driving instruction was given to the drivers. In this study, the
measured taxis were randomly hired at the origin without
any selection criteria. All the surveyed taxis were gasoline-
fuelled and the buses were diesel-fuelled. Smoking in public
transportation modes was strictly prohibited. And no com-
muter violated this regulation during samp ling under our
surveillance. On each survey trip, some useful information,
such as sampling time, travelling route, traffic condition,
number of passengers and weather condition, were clearly
recorded.
3. Sampling method and quality assurance
In-vehicle VOC samples were collected by stainless steel
adsorbent tubes (Tekmar, Part No. 14-1677-203). The
adsorption tubes has length of 7 in. and internal diameter
of 0.25 in., and were packed with Tenax TA and Carbosieve
S-III. Before sampling, all the adsorbent tubes were con-
ditioned at 225 jC at constant helium flow of 40 ml/min for
2 h. The tubes were then stored properly in protective glass
cartridges provided by the manufacturer. During sampling,
the adsorbent tube was connected to a portable low-flow
sampling pump (SKC). The flow rate of the pump was
adjusted to about 0.15 l/min. The vo lume of air sample
collected ranged from 4.0 to 9.0 l, depending on the journey
time of the trip. The sampling pump was calibrated by a
flow meter (Gilian, Gilibrator flow calibrator) before and
after each sample collection. The average of these two flow
Fig. 1. Location of the sampling routes.
L.Y. Chan et al. / Environment International 29 (2003) 429–435 431
rates was used as the sample flow rate in all concentration
calculations. In this study, no final flow rate shifted more
than 10% from the initial flow rate. The sampled tubes were
sent back to laboratory and stored in a refrigerator at 20
jC. All the VOC samples were analyzed within 3 days after
sampling.
The analyses of VOC samples from adsorbent tubes were
performed by thermal desorption (TD) and gas chromatog-
raphy/mass-selective detector (GC/MSD) technique. The
major components of the analytical system were a thermal
desorption system (Tekmar AEROTrap 6000), a gas chro-
matography system and a mass selective detector (Hewlett-
Packard, 5972 GC/MSD). A HP-VOC capillary column (30
m
0.32 mm
0.5 Am) was used with GC and pure helium
gas was used as carrier gas. The oven temperature of the GC
was initially held at 35 jC for 2 min. It was then raised to
250 jC at a rate of 8 jC/min and kept for 5 min finally. Each
target compound was identified by its retention time and
fragmentation pattern. The quantification of target VOCs
was accomplished by using multi-point external standard
curves. The analysis reports were checked for errors that
may be caused by the shifts in retention time.
The calibration curves were prepared by using 1 ppmv
standard gases (Scott Specialty, TO14 standard) a t five
different diluted concentrations plus zero air (0 50 ppbv).
Five sets of duplicate VOC samples were collected to check
the precision and reliability of the sampling and analyzing
method. The relative mean deviation of all duplicates was
within 12% for the target compounds. The method detection
limit (MDL) of the VOCs was defined as the product of the
standard deviation of seven replicate measurements at 1
ppbv and a Students t-test value of 3.143 (99% confidence
for seven replicates). The MDLs ranged from 0.42 to 0.96
Ag/m
3
for all measured VOCs. Other common quality
controls such as field blank check and breakthrough test
were also included.
4. Result and discussion
4.1. Inter-comparison of commuting microenvironments
Table 2 summarizes the statistical results of the aromatic
VOCs in different transports. None of the data obtained was
below their corresponding detection limit. By considering
the daily VOC levels in each commuting mode, there were
no significant differences (CV < 50%) in VOC concentra-
tions for the five-consecutive day measurements. Among
the target aromatic VOCs, toluene and benzene were the two
most abundant compounds in all surveyed tri ps. For the
benzene measured, the mean exposure level in taxis (33.6
Ag/m
3
) was the highest and was followed by air-conditioned
buses (13.5 Ag/m
3
) and non-air-conditioned buses (11.3 Ag/
m
3
). The benzene exposure level in the subway (7.6 Ag/m
3
)
was the lowest. The inter-microenvironment variations of
other target aromatic compounds were similar to that of
benzene. The taxi/air-conditioned bus/non-air-conditioned
bus/subway ra tio of the mean conce ntr ation w as a bout
4.4/1.8/1.5/1.0 for benzene and 3.4/1.7/1 .4/1.0 fo r total
BTEX. The results of the present study indicate that the
commuter exposure to aromatic VOCs greatly depended on
the mode of transport. Our results were consi stent with those
from Kingham’s et al. (1998), which reported that there
were significant differences in benzene exposure between
the modes of transport while commuting on a busy route in
Huddersfield, UK.
The VOC exposure levels in railway transport (subway)
were substantially lower than those in roadway transport
(taxi and bus). The averaged benzene and total BTEX levels
in roadway transport modes were 1.5 to 4.4 and 1.4 to 3.4
times higher than that in the subway, respectively. The in-
vehicle air quality of the subway was less and indirectly
influenced by vehicular emission on the street, since the
train travelled on its own underground track, which is
located away from busy street or other traffic. Hence, under
normal situation, the quality of tunnel air, as well as in-train
air, is better than roadway air.
The in-vehicle exposure levels in taxis were signifi cantly
higher than those in buse s f or the target VOCs. The
concentration differences between buses and taxis could
Table 2
Statistical results of target VOCs in different transportation modes
Compounds n In-vehicle concentration (Ag/m
3
)
Median Mean Range S.D.
(A) Subway
Benzene 10 7.0 7.6 4.1 13.2 4.3
Toluene 10 35.7 38.0 21.6 62.1 13.8
Ethylbenzene 10 5.8 5.6 2.9 6.9 1.9
m/p-Xylene 10 4.9 4.6 2.2 6.8 2.0
o-Xylene 10 5.4 4.7 2.2 5.9 1.6
Total BTEX 10 57.2 60.5
(B) Taxi
Benzene 10 34.5 33.6 22.4 47.9 10.6
Toluene 10 123.4 108.5 68.2 141.9 30.6
Ethylbenzene 10 19.1 20.3 12.5 29.4 6.9
m/p-Xylene 10 26.3 26.0 15.7 35.3 8.4
o-Xylene 10 16.2 17.2 10.6 24.9 5.9
Total BTEX 10 217.3 205.6
(C) Non-air-conditioned bus
Benzene 10 10.7 11.3 5.2 18.5 5.3
Toluene 10 48.5 48.9 23.1 75.3 17.8
Ethylbenzene 10 8.4 8.3 5.1 13.3 2.6
m/p-Xylene 10 9.8 10.6 7.4 15.3 2.8
o-Xylene 10 7.1 7.0 4.4 11.3 2.3
Total BTEX 10 83.5 86.1
(D) Air-conditioned bus
Benzene 10 13.0 13.5 6.6 21.5 4.9
Toluene 10 55.9 63.6 28.6 86.6 18.4
Ethylbenzene 10 7.2 8.2 4.6 12.3 2.6
m/p-Xylene 10 9.3 10.5 6.3 14.8 3.0
o-Xylene 10 6.1 6.9 3.9 10.4 2.2
Total BTEX 10 93.6 102.7
L.Y. Chan et al. / Environment International 29 (2003) 429–435432
be explained by a combined effect of fuel type, driving lane
and vehicle height. The in-vehicle BTEX levels in diesel-
fuelled vehicles would primarily impacted by the penetra-
tion of roadway air into the cabin (Jo and Yu, 2001). For the
gasoline-fuelled vehicles, due to the presence of target VOC
sources in gasoline, the engine evaporative emissions and
vehicle exhaust emissions from these vehicles are rich in
target aromatic compounds. Hence, self-contamination is
sometimes a crucial factor for their in-vehicle levels. As
most of the measured taxis have a fairly old vehicle age (>6
year) and have high mileage, the elevated VOC levels found
in these vehicles may be associated with the internal leakage
of engine evaporative emissions a nd/or veh icle exha ust
emissions through the structural faults and body cracks into
the vehicle interior. The selection of driving lane on the road
may also have a great influence on the in-vehicle levels.
Taxis and other light duty gasoline vehicles such as private
cars and motorcycles usually traverse in the middle lane of
the road (fast lane) where the roadway air is more seriously
contaminated by gasoline-related exhausts. On the contrary,
buses usually traverse near the curbside of the road (slow
lane) which is used extensively by other service buses, and
hence, the roadway air mainly contains diesel-related pollu-
tants. It is therefore, the in-taxi VOC levels would more
easily be elevated by infiltration of the exhaust of the
gasoline vehicles in front into the taxi interior especially
during stop-and-go traffic or idling at traffic lights. Apart
from this, the in-vehicle level may also be closely related to
the vehicle height. Vehicle exhaust is generated near the
road surface and the strength of pollutant source is higher
there. Since the height of the taxi cabin is lower than that of
the bus cabin, the bus commuters are comparatively less
affected by vehicle exhaust than the taxi commu ters.
The mean in-vehicle VOC levels in air-conditioned buses
and non-air-condition buses were close for all target com-
pounds except toluene. The higher toluene level in air-
conditioned buses may be due to the emission from the
internal casting and furniture of its interior, since some
measured air-conditioned buses are fairly new. Toluene is
a major constituent used as solvents in painting, surface
coating, vanishing and many product makings (Chao and
Chan, 2001). Regardless of the concentration difference of
toluene, the closeness in BTEX levels in these two different
ventilated buses infers that the window-closed and mecha n-
ical ventilation conditions in air-conditioned buses are
ineffective to minimize the intrusion of roadway VOC
sources. The traffic exhausts from neighbouring vehicles
can penetrate the bus interior through the air vent during
fresh air intaking from roadway air and through the doors
during opening of doors at intermediate stops.
4.2. BTEX ratios and correlations
The concentration profile and the inter-correlation of
BTEX compounds were examined. The average BTEX
ratios (B/T/E/X) in taxis, air-conditioned buses, non-air-
conditioned buses and subway were (1.0/3.2/0.6/1.3), (1.0/
4.7/0.6/1.3), (1.0/4.3/0.7 /1.6) and (1.0/5.0/0.7/1.2), respec-
tively. The target aromatic compounds were highly corre-
lated t o each other in the measured transports, with
correlation coefficient (r) ranging from 0.79 to 0.96 in taxi s,
from 0.80 to 0.96 in air-conditioned buses, from 0.76 to
0.94 in non-air-conditioned buses and from 0.42 to 0.85 in
subway. For the roadway transports, the similarity in con-
centration profile and the well inter-correlation of the target
compounds infer that the in-vehicle BTEX compounds are
mainly from the same source(s) in each commuting mode.
Emission from motor vehicles is expected to be the most
possible common major source in the measured microenvir-
onments. Adding to that, it is interesting to note that sub-
way, with its travelling route located in underground track
away from other traffic, has the concentration profile quite
similar to that in the roadway transports. This may be
attributable to the fact that traffic-related pollutants from
street-level ambient air can enter the underground tunnel
through air exchange (e.g. fresh air intake and infiltration of
air), and eventually reach the train cabin.
4.3. The effect of commuting time of day
The VOC level differences between two commuting
periods were exami ned by considering the non-peak-hour
to peak-hour exposure ratio. As shown in Table 3, the mean
ratio for all target compo unds ranged from 0.95 to 1.1 6 in
subway and 0.87 to 1.09 in taxi. In non-air-conditioned
buses and air-conditi oned buses, the rat io of the target
compounds was slightly lower, ranged from 0.75 to 0.88
and from 0.78 to 0.84, respectively. In general, the exposure
level was only slightly lower in non-peak-hour than in peak
hour for the measured transports. This can be explained by
the fact that traffic volume change on the selected routes
between the two time periods was small. Within the urban
area of Guangzhou, the roads are quite busy all the time.
This phenomenon is confirmed by the closeness of vehicle
speeds of a ll mea sure d r oadway transport. The driving
speeds of the surveyed buses and taxis rarely deviated more
than 5 km/h between afternoon and evening commutes
when running on the same route. Therefore, the difference
of vehicle emission strength on the measured routes
between the two set times may not be so large. Other than
the traffic volume, the concentration difference may also be
sensitive to the change of meteorological conditions (e.g.
mixing height, wind speed and ground temperature) and
vehicle-to-vehicle variation (e.g. extent of self-contamina-
tion).
4.4. Comparisons with oversea studies
Table 4 compares the present study with several recent
studies. To the best of our knowledge, there is no sim ilar
study carried out in Guangzhou or other cities of China in
the past. In general, the in-vehicle VOC levels obtained in
L.Y. Chan et al. / Environment International 29 (2003) 429–435 433
this study lay in the middle of the pollution range of these
studies. Based on the benzene measurements, the in-bus
level of the present study was close to the studies in
Go¨teborg (Barrefors and Petersson, 1996) and Paris (Dor
et al., 1995), but lower than the studies in Taegu (Jo and Yu,
2001; Jo and Park, 1999; Jo and Choi, 1996), Birmingham
(Kim et al., 2001), Huddersfield (Kingham et al., 1998) and
Sydney (Duffy and Nelson, 1997) and much lower than the
Taipei study (Chan et al., 1994). For taxi commuters, the
benzene exposure level in Guangzhou taxis was twice than
that in the Birmingham (Leung and Harrison, 1999) study,
but about 30% lower than the Korea (Jo and Yu, 2001)
study. The in-train benzene level was either comparable to
or lower than that in other studies (Kim et al., 2001;
Kingham et al., 1998; Barrefors and Petersson, 1996). The
differences between studies may be due to the inconsistency
of field study designs, driving conditions, meteorological
conditions and other related conditions (Jo and Park, 1999).
Therefore, careful consideration is required for direct com-
parison between studies.
4.5. Vehicle emission control and traffic condition
The vehicle emission controls and traffic conditions in
Guang zhou were reviewed. In Guangzhou, the inferior
engines and fuels used in the vehicles combined with the
inadequate use of catalytic converters are believed to the
causes of high in-vehicle VOC pollution in some commut-
Table 3
Mean in-vehicle VOC levels (Ag/m
3
) for non-peak hour and peak hour commutes
Compounds npk hr
a
pk hr
b
npk hr/pk hr
c
npk hr pk hr npk hr/pk hr
(A) Subway (B) Taxi
Benzene 7.4 7.8 0.95 33.2 34.0 0.98
Toluene 40.8 35.2 1.16 113.4 103.8 1.09
Ethylbenzene 5.8 5.3 1.09 19.1 21.5 0.89
m/p-Xylene 4.6 4.5 1.02 16.0 18.2 0.88
o-Xylene 4.9 4.5 1.09 24.3 27.8 0.87
(C) Non-air-conditioned bus (D) Air-conditioned bus
Benzene 10.6 12.0 0.88 11.8 15.1 0.78
Toluene 41.9 55.9 0.75 57.6 69.6 0.83
Ethylbenzene 7.2 9.3 0.77 7.2 9.1 0.79
m/p-Xylene 9.2 11.8 0.78 9.2 11.7 0.79
o-Xylene 6.3 7.8 0.81 6.4 7.6 0.84
a
npk hr = non-peak-hour exposure level.
b
pk hr = peak-hour exposure level.
c
npk hr/pk hr = non-peak hour to peak hour exposure level ratio.
Table 4
Comparisons with several oversea studies
Study Location Transport In-vehicle mean concentration (Ag/m
3
)
Benzene Toluene Ethylbenzene m/p-Xylene o-Xylene
Current study Guangzhou, China Subway 7.6 38.0 5.6 4.6 4.7
Taxi 33.6 108.5 20.3 26.0 17.2
Non-A/C bus 11.3 48.9 8.3 10.6 7.0
A/C bus 13.5 63.9 8.2 10.5 6.9
Jo and Yu (2001) Taegu, Korea Taxi 47.0 170.0 15.1 29.1 12.5
Bus 29.0 99.2 11.6 23.2 8.8
Kim et al. (2001) Birmingham, UK Train 24.3 64.9 5.6 18.0 5.0
Bus 20.2 69.3 8.0 27.9 8.6
Leung and Harrison (1999) Birmingham, UK Taxi 17.9 40.2 118.2 20.4
Jo and Park (1999) Taegu, Korea Bus 21.3 84.1 12.5 28.8 25.6
Kingham et al. (1998) Huddersfield, UK Train 12.9
Bus 21.2
Duffy and Nelson (1997) Sydney, Australia Non-A/C bus 30.0
A/C bus 25.0
Jo and Choi (1996) Taegu, Korea Bus 20.2 76.0 6.9 23.1 16.6
Barrefors and Petersson (1996) Go¨teborg, Sweden Bus 15.6 36.3
Train 8.1 15.6
Dor et al. (1995) Paris, France Bus 11 13 80
Chan et al. (1994) Taipei, Taiwan A/C bus 160 367 77 149 95
L.Y. Chan et al. / Environment International 29 (2003) 429–435434
ing trips. Recently, Fu et al. (2001) studied the vehicular
pollution in China and reported that the emission factor of
hydrocarbons from light-duty gasoline vehicles in China
was about five times higher than that in the United States.
They also stated that Chinese gasoline was generally more
evaporative than that from the US market. This would
result in high evaporative running loss emission in gaso-
line vehicles. Unsatisfactory vehicle maintenance is
another cause of concern. In ye ar 1999, as many as
200,000 vehicles were examined at on-road emission
inspection points, and more than one-third of them failed
the emission test (GZYEC, 2000). In addition to vehicle
emission controls, the slow-moving traffic pattern in
Guangzhou would also adversely affects the in-vehicle
air quality. Many vehicles in Guangzhou are congested
in urban districts. Hence, they travel with low driving
speed and frequent acceleration, deceleration and idling
(Zhang et al., 1999). Under this undesirable driving cycle,
the commuter exposure to VOCs is expected to be higher,
as the vehicular source strength is stronger and the inter-
vehicle distance is shorter.
5. Conclusion
This study measured the exposure level of traffic-related
aromatic VOCs in four major public transportation modes
while driving in urban areas of Guangzhou. The in-vehicle
level of VOCs is greatly influence d by the means of
transportation. The mean VOC exposure levels in roadway
transports were about several times higher than those in
railway trans port. Therefore, subway is highly recommen-
ded as a substitute for roadway transports. For roadway
transport, taxi commuters were found to be exposed to
higher VOC levels than bus commuters. Such differences
may be clos ely related to fuel type, driving lane and
vehicle height. The similar in concentration profile and
the high inter-correlation of target VOCs suggest that
vehicular emission is the major source of aromatic VOCs
found in the measured commuting microenvironments. In
this study, the influence of commuting time of day on in-
vehicle level is minor. In general, the VOC levels from
evening peak-hour commutes were only slightly higher
than those in afternoon non-peak hour commutes. The
results of this study indicate that Guangzhou commuters
are sometimes exposed to high levels of VOCs during
daily commutes. It is believed that the in-vehicle VOC
pollution is closely associated with the inadequate vehicle
emission control and slow-moving driving pattern. As this
preliminary study was limited in its scope and only
conducted in a 5-day period, the results are only indicative
and are mainly in preparation for a more comprehensive
study in the coming future.
Acknowledgements
This project is supported by a grant from the Hong Kong
Polytechnic University of the Hong Kong Special Admin-
istrative Region.
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    • "Because aromatic hydrocarbons, including benzene, toluene, ethylbenzene, and xylenes (collectively BTEX), are a major class of toxic VOCs [80][81][82], with a wide occurrence and distribution in both indoor and outdoor environments, and in both urban and rural areas, particularly in developing countries [83][84][85][86][87][88][89][90] , BTEX were chosen as model toxic VOCs during our measurements of respiratory AFs. Another reason for choosing BTEX as our target VOC group is that humidity effects in breath samples can be ignored when measuring BTEX by PTR-TOF-MS, as previous studies have shown little humidity dependence on their sensitivity [91][92][93]. "
    [Show abstract] [Hide abstract] ABSTRACT: Respiratory absorption factors (AFs) are essential parameters in the evaluation of human health risks from toxic volatile organic compounds (VOCs) in ambient air. A method for the real time monitoring of VOCs in inhaled and exhaled air by proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) has been developed to permit the calculation of respiratory AFs of VOCs. Isoprene was found to be a better breath tracer than O2, CO2, humidity, or acetone for distinguishing between the expiratory and inspiratory phases, and a homemade online breath sampling device with a buffer tube was used to optimize signal peak shapes. Preliminary tests with seven subjects exposed to aromatic hydrocarbons in an indoor environment revealed mean respiratory AFs of 55.0%, 55.9%, and 66.9% for benzene, toluene, and C8-aromatics (ethylbenzene and xylenes), respectively. These AFs were lower than the values of 90% or 100% used in previous studies when assessing the health risks of inhalation exposure to hazardous VOCs. The mean respiratory AFs of benzene, toluene and C8-aromatics were 66.5%, 70.2% and 82.3% for the three female subjects; they were noticeably much higher than that of 46.4%, 45.2% and 55.3%, respectively, for the four male subjects.
    Full-text · Article · Dec 2016
    • "For example, the average PM 2.5 and PM 10 concentrations at subway platforms in Stockholm, Seoul, and Los Angeles Fig. 5. Variation of the PM 2.5 concentration over time at different sampling positions on the platforms (Fig. 3were 260 and 470 lg/m 3 , 129 and 359 lg/m 3 , and 57 and 78 lg/m 3 , respectively (Johansson and Johansson, 2003; Park and Ha, 2008; Kam et al., 2011). The average PM 2.5 and PM 10 concentrations inside subway trains in Hong Kong and Guangzhou were 39 and 50 lg/m 3 and 44 and 55 lg/m 3 , respectively (Chan et al., 2002Chan et al., , 2003). Ye et al. (2010) measured the mean PM 2.5 and PM 1.0 levels at certain platforms along Shanghai subway Line 1 and Line 2 (287 and 231 lg/m 3 respectively) and Lu et al. (2015) measured the range of PM 2.5 concentrations at three platforms of Shanghai subway Line 7 (which ranged from 49.2 to 66.2 lg/m 3 ). "
    [Show abstract] [Hide abstract] ABSTRACT: More than 9 million passengers take Shanghai’s subway system every work day. The system’s air quality has caused widespread concern because of the potential harm to passengers’ health. We measured the particulate matter (PM) concentrations at three kinds of typical underground platform (side-type, island-type, and stacked-type platforms) and inside the trains in Shanghai’s metro during 7 days of measurements in April and July 2015. Our results demonstrated that the patterns of air quality variation and PM concentrations were similar at the side-type and island-type platforms. We also found that the PM concentrations were higher on the platforms than inside the train and that the PM concentrations in the subway system were positively correlated with those in the ambient air. Piston wind generated by vehicle motion pushes air from the tunnel to the platform, so platform PM concentrations increase when trains approach the platform. However, the piston wind effect varies greatly between locations on the platform. In general, the effect of the piston wind is weaker at the middle of the platform than at both ends. PM concentrations inside the train increase after the doors open, during which time dirty platform air floods into the compartments. PM1.0 and PM2.5 were significantly correlated both inside the train and on the platforms. PM1.0 accounted for 71.9% of PM2.5 inside the train, which is higher than the corresponding platform values. Based on these results, we propose some practical suggestions to minimize air pollution damage to passengers and staff from the subway system.
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    • "Indeed, a previous study comparing the levels of benzene, toluene, ethylbenzene, and xylene in air-conditioned and non-air-conditioned buses showed that the levels of these tested compounds in air-conditioned buses were 59.3%, 59.1%, 60.1%, and 60%greater than those in non-air-conditioned ones, respectively [22]. In contrast, another study examined the exposure levels of traffic-related VOCs in four popular public commuting modes and showed that there was no significant difference between air-conditioned buses (13.5 µg/m 3 ) and non-air-conditioned buses (11.3 µg/m 3 ) [32]. Accordingly, the effect of air conditioning on interior air pollution warrants further investigation; we recommend that the natural ventilation of air-conditioned coaches must be further increased for an appropriate period while the coaches are running. "
    [Show abstract] [Hide abstract] ABSTRACT: An air-conditioned coach is an important form of transportation in modern motorized society; as a result, there is an increasing concern of in-vehicle air pollution. In this study, we aimed to identify and quantify the levels of volatile organic compounds (VOCs) and carbonyl compounds (CCs) in air samples collected from the cabins of newly produced, medium- and large-size coaches. Among the identified VOCs and CCs, toluene, ethylbenzene, xylene, formaldehyde, acetaldehyde, acrolein/acetone, and isovaleraldehyde were relatively abundant in the cabins. Time was found to affect the emissions of the contaminants in the coaches. Except for benzaldehyde, valeraldehyde and benzene, the highest in-vehicle concentrations of VOCs and CCs were observed on the 15th day after coming off the assembly line, and the concentrations exhibited an approximately inverted U-shaped pattern as a function of time. Interestingly, this study also showed that the interior temperature of the coaches significantly affected the VOCs emissions from the interior materials, whereas the levels of CCs were mainly influenced by the relative humidity within the coaches. In China, guidelines and regulations for the in-vehicle air quality assessment of the coaches have not yet been issued. The results of this study provide further understanding of the in-vehicle air quality of air-conditioned coaches and can be used in the development of both specific and general rules regarding medium- and large-size coaches.
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