Extended Air Quality Sampling at OSU
Bus Stops
Theresa Hauser
Contents
Background: .................................................................................................................................................. 2
Health Effects ............................................................................................................................................ 2
Previous Studies ........................................................................................................................................ 3
Current Project.......................................................................................................................................... 5
Methods: ....................................................................................................................................................... 6
Results: .......................................................................................................................................................... 7
Conclusions: ................................................................................................................................................ 10
References: ................................................................................................................................................. 14
1
Background:
Health Effects
Public buses are useful because they eliminate the need for everyone to drive, thus
reducing traffic congestion and decreasing pollutants emitted by cars. According the state of
Delaware, buses emit about 20% as much carbon monoxide per passenger mile compared to a
car with a single passenger. Riding the bus is also considered a form of active transportation and
can lead to a decreased risk of being overweight and obese (American Public Health
Association). However, several studies have shown that buses are significant contributors to air
pollution (Kaur et al, 2007; Jackson & Holmén, 2009). One way that buses contribute to
pollution is through particulate matter (PM) emissions. PM is regulated by the National Ambient
Air Quality Standards (NAAQS) (Moore et al, 2012). This type of pollution has been tied to
adverse health effects such as chronic asthma, eye and throat irritation, and respiratory problems
(Nauss, 1995; de P. Pereira et al, 2001). One study has estimated that reducing particle pollution
by 1 µg/m3 annually could prevent 35,000 deaths a year in the US (Lepeule et al, 2012). These
problems are made worse by the fact that diesel exhaust particles (DEP) are usually <2.5 µm,
which means they are highly respirable and can settle deep in the lungs (See et al, 2013; US
EPA, 2013).
In addition, polycyclic aromatic hydrocarbons (PAH’s) tend to attach to particle matter
and can thus be absorbed into the body (US EPA). One PAH of concern is benzo (a) pyrene,
which can cause developmental and reproductive effects for chronic exposures above the
maximum contaminant level of 0.0002 mg/L (US EPA). According to the American Lung
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Association, those at highest risk for health issues caused by PAH exposure are children, adults
over 65, and people with illnesses such as heart disease, COPD, and diabetes (2013).
Several other types of compounds are also emitted by buses. For example, volatile
organic compounds (VOCs) such as benzene, methyl tertiary butyl ether (MTBE), toluene, ethyl
benzene, xylene and styrene are common emissions (Kongtip et al, 2012). Benzene is of special
interest because it can cause cancer; in particular, it has been associated with leukemia
(American Cancer Society, 2010). MTBE is found in gasoline and is associated with headaches,
nausea, and dizziness (New Hampshire Department of Environmental Services 2009). Buses also
emit carbon dioxide and carbon monoxide. CO2 can be dangerous because high levels can cause
headache, dizziness, and even oxygen deprivation (Wisconsin Department of Health Services,
2012). Exposure to CO can also cause oxygen deprivation, due to reduced transport of oxygen
throughout the body, and chest pain (US EPA, 2012).
Previous Studies
Exposure to air pollution varies based on the mode of transportation used (Moore et al,
2012). This project involved looking at exposures to those who use the OSU Campus Area Bus
Service. Several studies have looked at emissions from buses and health. One such study was
done with school buses (Beatty & Shimshack, 2011). This study was conducted after a program
had been implemented that installed retrofits, which are devices designed to reduce the pollution
emitted by school buses. It found that the areas with pollution reduction programs experienced
significant declines in asthma and bronchitis cases.
Another bus study attempted to look at whether using bioethanol contributed to more
pollution than normal gasoline (López-Aparicio & Hak, 2013). Ambient air quality measurement
for NO2, O3, acetic acid, formaldehyde and acetaldehyde were taken at areas exposed to
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bioethanol traffic and in areas without exposure. VOC measurements were also recorded at the
exhaust pipes of buses. The results implied that areas with bioethanol traffic were exposed to
higher levels of acetaldehyde, which may lead to the development of cancer.
One study looked at exposure on buses. This study was conducted in Thailand and
measured exposure levels to PM2.5, PM10, CO2, CO, and VOCs for bus drivers (Kongtip et al,
2012). Samples were collected for a full shift. They found that drivers of buses without A/C were
exposed to higher levels of PM2.5 than drivers of buses with A/C but the reverse was true for
PM10. They also learned that PM2.5 levels were above WHO recommendations. CO2 levels were
also higher while CO levels were below the recommendations. The drivers were exposed to
VOCs such as benzene, ethyl benzene, and MTBE. Overall, they found that bus drivers are
exposed to high levels of air pollution.
More similar to this project, a study in Singapore was conducted at bus depots (See et al,
2006). This study was conducted at the bus station in order to reduce the chance of measuring
pollution emitted by automobile traffic. Measurements were taken 1.5 m off the ground to
represent the breathing zone. This study found that during hours of operation, bus stations had
much greater levels of particulate matter and PAH’s.
A study done in Salvador, Brazil was conducted at covered bus stations (de P. Pereira et
al, 2002). Samples were collected throughout the day in order to obtain measurements at low and
high traffic times. Levels of PAH’s and their identity were recorded using twelve samples but the
procedures used to collect these samples is not described in detail. The researchers found that
higher traffic times led to higher levels of pollutants and less busy times had lower levels of
pollution. In this study, measurements were collected at ground level. This might be an issue
because it might not represent human exposure.
4
In Buffalo, NY it was found that several factors affected human exposure to particulate
matter (Hess et al, 2010). Such factors included waiting location (inside bus shelter or outside),
the presence of smoking, and time of day. To conduct the study, they measured 840 consecutive
minutes of PM levels inside bus shelters and outside. They found that PM concentrations
differed between the outside and inside of the bus stop shelter. They also found that bus stop
placement affected exposure because stops in open spaces were exposure to less PM. They did
not indicate whether buses were present or absent during their study.
Another project looked at the effect of shelter orientation on PM levels at bus stops in
Portland, OR (Moore et al, 2012). This study also measured PM levels and collected data in both
the afternoon and morning. Unlike the Buffalo study, the researchers took traffic flow and wind
direction into account. They found that bus stops that faced the road were exposed to higher
levels of PM than shelters that faced away from it.
Current Project
This project will attempt to characterize exposure to pollutants by measuring the air
quality at bus stops on the Ohio State University campus. It will investigate whether the presence
of buses does indeed increase the level of pollutants at the stops. Because several other studies
looked at the differences between levels in the morning and in the afternoon, this will also be
investigated. The difference in air quality under the actual shelter and outside of it will also be
looked at. In addition, the type of buses presents at different times will be noted. This will allow
us to determine if there is a difference in pollutant levels for hybrid buses and normal buses.
5
Methods:
This project is an extension of an earlier project. The previous project collected data
points at bus stops when buses were absent and then collected data when buses were present but
only a few measurements were collected at a time at each stop. This project should provide a
better overall picture of the effect of buses on air quality and human exposure at bus stops
because data was collected continuously for three hour intervals at the same bus stop.
Three pieces of equipment were used. The MultiRAE Plus was used to measure levels of
VOCs and CO in parts per million. It was programmed to record measurements every 60
seconds. The TSI VELOCICALC® Air Velocity Meter Model 9555 Series was used to measure
levels of CO2, also in parts per million. This was also programmed to record measurements every
60 seconds. Lastly, the TSI Aerotrak 9306 was used to measure PM0.3 and PM1 in particles per
cubic foot. It takes one minute to collect a sample and also took samples every 60 seconds.
For each sampling interval, the equipment was set up on a newspaper stand at the bus
stop to stimulate human exposure. The stands are located on the outside of the bus shelters facing
the streets. Only bus stops with shelters and newspaper stands were sampled for this project.
Three stops were used: CarMack 4, St John Arena, and the Ohio Union bus stop. The same stop
was sampled for the entire three hour interval. Each stop was sampled on two different days,
once in the morning and once in the afternoon.
While equipment measured pollutant levels for the three hours, the time when buses
arrived were recorded. To do this, the time was noted when buses pulled into the stop and when
they pulled away. In addition, the type of bus (normal, hybrid, or COTA) and the number of
buses (IE, if more than one bus pulled up at the same time) were also recorded. Weather
conditions and the location of the stop were also documented.
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After collecting the data for outside the bus shelter, data was collected under the shelter
for one two hour period at each bus stop. This is useful information because some bus riders wait
under the shelter until their bus comes. They maintain under the shelter if the bus that pulls up is
not the one they are waiting for. Thus, collecting measurements under the shelters and outside of
them will enable us to better characterize exposure. It will also allow us to see if there is a
significant difference between exposure under the shelters and outside the shelters. When data
was collected under the shelters the equipment was set on the bench that is located along the
back wall.
After data collection, the data was combined in an excel spreadsheet. Average values
were found for all pollutants measured. Trends in pollutant levels were compared based on
whether buses were present and these differences were analyzed for significance by conducting a
T test. In addition, the difference between average pollutant levels in the morning and average
levels in the afternoon were compared. Furthermore, differences between the types of buses were
analyzed using a T-test. The three bus stops visited also were compared in order to determine
which stop had the highest levels. The daily trends in pollutant levels were also graphed for
comparison.
Results:
There were low levels of VOCs and CO outside the bus shelters but levels of PM and
CO2 were much higher. The average CO2 level, regardless of bus presence, was about 315 ppm.
Overall, it was found that only levels of CO2 increased significantly outside the shelter when
buses were present (p=0.02). Levels of PM 1 also increased when buses were present but not by a
significant amount (Table 1). Levels of CO2, VOCs, and PM1 decreased from morning to
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afternoon while CO and PM0.3 increased (Table 2). Levels of PM0.3 fluctuated the most between
the morning and afternoon. PM1 was the only pollutant that did not significantly change at
different times.
Pollutant
Bus Present?
Yes
No
VOC
CO
CO2
PM0.3
PM1
0.67323 0.74159292 317.5212 2026471.08 36444.50
0.679674 0.713353116 312.9031 2103555.18 35577.32
Table 1: Average Values outside Shelter Based on Bus Presence
Pollutant
Time
Morning
Afternoon
VOC
CO
CO2
PM0.3
1.268656716 0.434515 331.3363803 785048
0.139661017 0.988305 299.6428571 2279060
PM1
36304.28
35602.95
Table 2: Average Values of Pollutants by Time of Day
CO, PM1 and PM 0.3 levels were highest for public buses (Table 3). CO2 levels were
highest for hybrid buses while VOCs were slightly higher when normal campus buses were
present. Overall, the public buses seemed to affect air quality the most. The Ohio Union Bus stop
had the highest levels of VOCs, CO, and PM0.3 (Table 4). The particulate matter at this stop may
be higher due to construction across the street from the bus stop. The CarMack bus stop had the
highest levels of CO2 while the St John Arena stop had the highest levels of PM0.3. In fact, the
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PM0.3 levels at the St John Arena are more than twice that of the next highest site. This stop was
located near a roadway so perhaps this may have contributed to the higher PM counts.
Pollutant
Bus Type
Normal
Hybrid
COTA
VOC
CO
CO2
PM0.3
PM1
0.728938 0.7263736 318.0493 1939658.56 35042.55
0.553
0.718
328
2047352.98 36469.36
0.642308 0.8141026 297.6282 2319316.10 43083.41
Table 3: Average Values by Bus Type
Pollutant
Site
CarMack
Ohio Union
St John Arena
VOC
0.01547619
1.520833333
0.003
CO
CO2
PM0.3
PM1
0.375297619 336.8071 1625607.4 13424.46
0.94077381 312.2567 1038433.1 58825.95
0.841310541 289.1834 3372594.1 38168.01
Table 4: Average Values outside Shelter for each Location
Unlike the measurements taken outside the bus shelter, the results show that there was a
significant difference in pollutant levels at the stop when buses are present versus when there is
no bus for VOCs, with buses increasing the level (p=0.04). Unlike the results outside the shelter,
there was an insignificant difference in CO2 levels at the stop inside the shelter when buses were
present versus when they were not. The average CO2 level when buses were present was 325
ppm; when buses were absent it was 319 ppm (Table 5). There was no difference in the level of
CO, PM 0.3, or PM 1 based on the presence of buses. There was a significant difference in
measurements taken under the shelter and outside of it at the bus stops for all of the pollutants
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but PM 0.3. Levels of CO2 and VOCs were higher under the shelter while levels of PM1 and CO
were higher outside the shelter (Table 6).
Pollutant
Bus Present?
Yes
No
VOC
CO
CO2
PM0.3
PM1
1.818349 0.383486 324.5876 2239929 30216.06557
1.482803 0.36242 319.6133 2179552 28708.76712
Table 5: Average Values under Shelter Based on Bus Presence
Pollutant
Location
Under
Outside
VOC
CO
CO2
PM0.3
PM1
1.62030075 0.371053 321.3489 2207037 29394.93
0.67708703 0.724689
315
2070984 35943.73
Table 6: Average Values under Shelter vs. Out
Conclusions:
The results show that overall, air quality outside the bus shelters does not change based
on the presence of buses. The exception was CO2, which is only dangerous at high levels. The
average level measured was 315ppm, which was within the range of average outdoor air
(Wisconsin Department of Health Services, 2012). Under the shelter, levels of VOCs increased
significantly with the presence of buses, but the level was low enough not to warrant concern
(1.82 ppm). Thus, buses do not necessarily have a large negative impact on public health by
increasing pollutant levels at bus stops above background levels. This means that using different
buses or having more regular maintenance would not necessarily affect the levels of pollution
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that bus riders are exposed to. Installing retrofits might reduce the CO2 exposure but since the
levels were not dangerous it does not seem necessary.
The results also show that those who ride the buses are exposed to very low levels of
VOCs and CO. The levels of VOCs inside the shelter significantly changed when buses were
present but the levels were still very low. This is a positive finding since VOCs can cause
numerous health issues. However, bus riders are exposed to high levels of particulate matter,
although this exposure does not seem to be based on whether buses are present or not. Particulate
matter can exacerbate health issues so decreasing this exposure could be beneficial. Since buses
are not necessarily contributing to this exposure changes to buses would not be very helpful.
Instead, one possible way to decrease exposure is to consider orienting the bus stops differently.
One study looked at orientation and found that when the shelter faced away from the street, i.e.
when the covered side faces the street, commuters are exposed to less pollution (Moore et al,
2012). Perhaps this could be a first step in reducing exposure levels. This might be especially
helpful at stops near the road, like St. John Arena.
Measurements were taken just outside the shelter as well as under the shelters because
previous studies found that measurements differed between outside bus shelters and inside of
them (Hess et al, 2010; Moore et al, 2012). Since many bus riders sit inside the shelter while
waiting for the buses it was beneficial to measure levels inside the shelter and to compare them
to levels outside in order to get a better estimate of average exposure. This was especially
important because the previous study found that levels of particulate matter were higher in the
shelter versus outside, even though one of the studies mentioned that it could be due to cigarette
smoking. This study also found this to be true for CO2. In addition, levels were higher for VOCs
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under the shelter, although the levels were quite low. This supports the idea of orienting the bus
stops differently to reduce exposure since levels were often higher inside.
The fact that levels for some pollutants differed so much in certain areas implies that
other things in the environment play a role in exposure. For example, the high levels of PM1 at
the Union may be from the construction site. The levels of PM at the St John Arena site could be
due to the nearby road. This could warrant further research into other factors that affect exposure
since the buses themselves did not increase the levels of pollutants by much.
The time of day was also related to exposure. Most importantly, PM0.3 significantly
increased from morning to afternoon. This may be related to increased traffic, although it would
be expected that the traffic would be heaviest in the morning when people are commuting to
work. This could be the case for CO2 since it decreased from morning to afternoon. The higher
PM0.3 levels could also be caused by increased activity in general later in the day. This would
require further study but based on the results it might be beneficial to recommend that those with
respiratory illnesses ride the bus earlier in the day to decrease particulate matter exposure.
One concern with this project is that the exhaust pipes on the buses are located on at the
top of the bus. This might mean that the pollution is being spread out more and the equipment is
not able to properly measure the emissions. However, it should represent the average exposure at
the bus stops if not what is actually emitted by buses. Also, the results are only for a few of the
pollutants that buses emit. There could be effects from chemicals not measured and these levels
could significantly increase when buses are present.
Another possible issue is that buses run rather regularly. This might mean that the
pollutants they emit might not be dispersed out of the area before the next bus comes. Thus, in
the future it might be a good idea to take measurements when the buses are not running or are
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only running on a limited schedule, such as on a holiday, so that the background level can be
found. One issue with this is that normal traffic may also be lessened and thus it might be hard to
say that the difference is only from the absence of the buses. However, this study was done in the
summer when there was more time between buses which should have allowed more time for
pollutants to disperse between buses.
Another possible problem is that wind direction and speed plays a role in the dispersal of
pollutants. Wind direction was not measured at the site but was obtained for the city as a whole.
However, a thorough analysis would need to be done in order to determine the direction of the
wind with regard to the location of the bus stops. This might be a good idea because the results
imply that other factors, such as wind speed and direction, might play a larger role than the
presence of buses.
In the future it would be interesting to investigate exposure on the buses. This would
provide a picture of what the drivers are being exposed to. Since drivers might be exposed for
most of their work day it might be useful to conduct continuous sampling as well. A previous
study looked as bus driver exposure and found that drivers were exposed to high levels of
pollutants. It also might be interesting to compare seasonal exposures, both on and off the buses.
For example, using the air conditioner in the summer versus using the heater in the winter might
result in different exposure levels. Since air quality can have a large impact on everyone, such
projects might be interesting to explore in the future.
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