The Investigation of Air Quality on Buses

| October 22, 2018

The Investigation of Air Quality on Buses


Ip Siu Wa

Submitted in partial fulfilment
of the requirement for the degree
BSc (Hons) Building Service Engineering

Leeds Metropolitan University
June 2014

Section Page
1. Abstract…………………………………..……………………………. 3
2. Introduction
……………………………………………………………. 3
3. Objectives………………………. ……………………………………… 4
4. Literature Review………………………. ……………………………… 5
Sick Building Syndrome (SBS)
………………………..….….…… 9
Building-Related Illness (BRI)…………………………….….…… 10
Absenteeism and Sick Leave………………………..…….….…… 11
5. Study for Bus Company Air
Quality Control………………….……… 12
6. Methodology……………………………. ……………………………… 14
7. References…………………………………….………………………… 17
8. Appendix

1. Abstract
Hong Kong is one of the cities in Asia
where public transport is the major commuting mode. Over 90% of the population relies greatly on public transport to
go to their work place, school or recreational places. Among different public transportation
modes, about 38% of the passengers
use the franchised buses according to the statistic data from Transport
Department. It is one of the most popular commuting mode in Hong Kong as it
provides a convenient access to all districts. Since the passengers are
required to spend a considerable time inside vehicle compartment, the air
quality and thermal comfort inside the buses should be considered. From the announcement by bus operators, over 95% of
buses are air-conditioned type. Therefore, the air-conditioned type will be
focused in this research project.

2. Introduction
In Hong Kong, there is no
specific regulation on the air quality inside in-service air-conditioned buses
under the bus franchises or the existing environment/transport-related
legislation. However, the government has set up an inter-departmental Indoor
Air Quality Management Group (IAQMG) chaired
by the Planning, Environment and Lands Bureau and comprising the members from
other relevant policy bureaus and departments to coordinate various activities
and programmes related to indoor air quality. The IAQMG has developed a
guideline in 2003, in the form of professional practice notes for managing the
air quality in air-conditioned bus (EPD, 2003).
This guideline states the in-bus air quality standards as well as practical
recommendations about the air temperature and relative humidity ranges for
air-conditioned buses in Hong Kong. But the intent of this guideline is not to
act as strict regulations but rather as recommendation for bus operators. It uses
the concentration of carbon dioxide as an indicator for monitoring the air quality
in bus compartment. But it does not consider the other air pollutants (e.g.
carbon monoxide) which can also been found in buses. It recommends controlling
the thermal environment by keeping the air temperature ranging from 20 to 28°C
and the relative humidity ranging from 40 to 70%. The local bus operators only
control in-bus air quality and thermal environment by conforming to the
prescribed levels stated in the guideline. As a result, the settings are merely
adjusted to fulfill the guidelines, rather than to satisfy the passengers’
thermal comfort and air quality.

3. Objectives
In this project I would like to study the indoor air
quality in the buses, the objectives were as
To measure the pollution levels for in-bus
environment with the comparison the standards in Hong Kong.
To measure the common thermal parameters with
the comparison the standards in Hong Kong.
To conduct face-to-face surveys to get the
passengers’ preferences and satisfaction regarding the in-bus thermal comfort.
To check whether the current standard in Hong
Kong is consistent with passengers’ preferences and satisfaction.
Publishing a set of Guidance Notes for the
better management of IAQ in bus
4. Literature Review
Clean air
is considered to be a basic requirement of human health and well-being.
However, air pollution continues to pose a significant threat to health
worldwide. According to a WHO assessment of the burden of disease due to air
pollution, more than 2 million premature deaths each year can be attributed to
the effects of urban outdoor air pollution and indoor air pollution (caused by
the burning of solid fuels). More than half of this disease burden is borne by the
populations of developing countries.
The Practic
Note for Managing Air Quality in Air-Conditioned Public Transport Facilities –
Buses (PN-B) has been established in 2003 by Environmental Protection Department (EPD) to provides guidelines to professional
persons on the management of air quality in air-conditined bus facilities
operated within the territory of Hong Kong by the Hong Kong franchised bus
companies. One of the key function for PN-B is to provide a controlling
parameters and limits to indicate better air quality in bus facilities. It uses
Carbon dioxide (CO2)as a
surrogate indicator as its concentration in an indoor environment is a good
indicator of the effectiveness of ventilation system and the adequacy of
ventilation. The PN-B set a two-level of concentration of CO2 for
evaluating and assessing air quality in bus facilities. The two-level air
quality guidelines are as follows:

Level 1 (less than or equal to 2.500 ppm or 4.500 mg/m3)
– represents good air quality of a comfortable bus facility at which there is
no health concern identified.

Level 2 (less than 3.500 ppm or 6.300 mg/m3) –
represents the air quality of a bus facility at which there is no health concern identified.


Air Quality Guidelines (Hourly average)



Carbon dioxide

2.500 ppm (4.500mg/m3)

3.500 ppm (6.300mg/m3)

According to the current air quality standard for outdoor condition in Hong Kong by EPD (AQ-Comparison)(EPD), the concentration of CO2
should not be over 800 mg/m3 for average exposure time of 1 hour. Obviously,
the setting levels in PN-B are too low comparing with the standard which is the
multiple of about 5 to 8 of it. Unfortunately, With reference to the new release
(Green Sense, 2009) by an association, Green Sense, in 2009, some of the bus
route cannot fulfill the lowest level in PN-B. They have conducted a
measurement of the concentration of CO2 for nine numbers of buses
and found that the highest concentration of CO2 for one of the buses recorded
as 3623 ppm. The high concentration of CO2 indicated that the bad effectiveness
of ventilation system. It may cause headaches, flu symptoms, fatigues to the
passengers. If the bus driver suffers such symptoms, it may affect the life
safety for passengers.
Carbon monoxide is an extremely toxic gas which interferes with the
oxygen transport capacity of blood. It can cause cardiovascular diseases and
symptoms such as headaches, concentration problems, flu symptoms, nausea,
fatigue, rapid breathing, chest tightness and impaired judgment. Since there is no any standard of carbon monoxide for
in-bus condition, the table 3-1 Relevant Parameters in Hong Kong (Ambient) Air
Quality Objectives in Guidance Notes for the Management of Indoor Air Quality
in Offices and Public Place (GN-IAQ)(EPD)is referenced. The concentration of Carbon Monoxide should
be less than 10000 µg/m3 (8.7 ppmv) to reach the “Good Class”
The PN-Bus
states the in-bus air quality standards as well as practical recommendations
about the air temperature and relative humidity ranges for air-conditioned
buses in Hong Kong. It recommends controlling the thermal environment by
keeping the air temperature ranging from 20 to 28 °C and the relative humidity ranging from 40 to
70%. Furthermore, it is recommended that air quality managers from the bus
company should adjust these ranges by taking the passengers’ preferences into
consideration. The main objective of the PN-Bus focuses on the control of
in-bus air quality to achieve a safe and healthy in-bus environment, while the issue
of thermal comfort is merely briefly stated in the appendix. Considering the
in-bus thermal environment, the recommended ranges by PN-PTF lie within the
comfort zone stated in ASHRAE Standard 55-2004 (ASHRAE,
temperature has the most direct effect on thermal comfort. While Humidity
influences thermal comfort by affecting the human body’s ability to lose body
heat through perspiration. In humid conditions it is more difficult to lose
heat – the effect is therefore the same as raising the temperature and people
feel “sticky”. Low relative humidity causes eyes, noses and throats to dry
which may lead to discomfort, irritation and increased susceptibility to
One of the other
factors affecting the thermal comfort is air movement. A certain amount of air
movement round the human body is essential for thermal comfort. It is also
important in dispersing air pollutants. The required level of airflow depends
on the air temperature and humidity. In the hot and humid summer months, for
example, greater air movement can help produce a more comfortable environment.
Airflow is determined by ventilation and convection currents (created by hot
air rising and cool air falling) in the compartment. Blocked or unbalanced
ventilation systems, or too low pressure levels in ventilation ducts may
restrict air movement, producing a “stuffy” atmosphere which makes passengers
feel uncomfortable. Too much air movement results in draughts and excessive
cold. Since there is no any standard of air movement for in-bus condition, the
table 3-2 IAQ Objective for Office Buildings and Public Places in GN-IAQis referenced.
The air movement should be less than 0.3 m/s
to reach the “Good Class” standard.

All the requirement of air quality
/ thermal parameters is summarized as below. The research data should be
referred in order to reach the “standard”.

Thermal / Air Parameter Standard
CO2 Level 1 (less than or equal to 2500 ppm)
Level 2 (less than 3500
CO Less than 8.7 ppm
Temperature From 20 to 28 °C
Humidity From 40 to 70%
Air Velocity Less than 0.3 m/s

Sick Building Syndrome (SBS)
Sick Building
Syndrome is a term giving to a range of non-specific symptoms expressed by
building occupants that are apparently finked to the time they spend in the
building, but in which no specific causes can be identified (Sykes, 1989). The
symptoms of SBS include:

and itching of the eyes
Nose and
throat irritation
Runny or
congested nose
flu-like symptoms
Itchy skin
occasionally with the development of rash
dizziness, nausea

The above symptoms
are often nonspecific, subjective and often found in the building that forced
ventilation or central air conditioning is present. Most studies have shown
that an air-conditioning and ventilation system is the major problem in most of the sick buildings. The investigation of the U.S.
National Institute for Occupational Safety and Health in 1987 has found that
over 50 % of the sick buildings surveyed were suffering from inadequate
ventilation (Robertson, 1990). The building occupants often suffer from the
symptom singularly of in combinations while the symptom will disappear after
the occupant leaves the building (Benda and Ga., 1999).

Building-Related Illness (BRI)
Building-Related Illness
(BRI), same as SBS, is the group of illnesses that may be related to indoor air
quality problems. BRI is the illness that results from exposure to the
environmental agents in the building air in which symptoms of diagnosable illness
are identified.
Some examples of BRI
are shown below:

Pontiac fever
caused by LegionellaSpp.
disease caused by Legionella
pneumonitis caused by certain species of fungi
fever caused by fungi, bacteria, protozoa, microbial endotoxins and arthropods.

Disease (LD) is the most widely published BRI that first recognized in 1976
after an outbreak occurs in Philadelphia hotel claiming 29 lives out of 182
people infected (ACVA Pacific Pty. Ltd.). Recent reports have shown that there
an around 300 cases in U.K. and 150 cases in Australia reported annually while
75% of that was sporadic cases (Health & Safety Commission, U.K., 1991).
The sources of LD infection were usually traced to building water systems
mainly involving cooling towers and humidifiers of air-conditioning systems.
The disease is a form of serious pneumonia caused mainly by the Legionella
pneumophila that survives well in warm and wet environment. Good housing
keeping, correct design, safe operation and proper maintenance of building
services systems and equipment will control the proliferation of Legionella and
minimize the risk of LD (EMSD, 2013).

Absenteeism and Sick Leave
As stated by Sundell, J (1990), the importance
of the workers’ symptoms should not be underestimated, because there is a
strong relationship between workers’ complaints of ill health and absence due
to sickness (Preller, L.,1990). That meant that a worker’s perception that the
working environment is bad or unhealthy has economic costs, because it may lead
to diminished productivity (Zyla-Wisensale and Stolwijk, 1990).
Preller, L. (1990) found that several factors
were significantly related to absenteeism in general and to sick leave due to
sick building symptoms. Several personal characteristics were related to most
or all aspects of sick leave. Environmental or work related factors showed in
some cases a significant relation with sick leave. People, who were able to
adjust the temperature in their workplace, reported fewer sick leaves than
people who could not. In case of absenteeism because of symptoms regarded as
being part of SBS, more significant relations with environmental and work related
factors were found. Both steam and spray humidification was related to the
number of times and days of absenteeism/sick leave. A significant relation
existed with self-adjustable temperature. Because it was believed that the rate
of the absenteeism might be controlled by means of increase in the outdoor air
ventilation rate.
5. Study for Bus Company
Air Quality Control
According to the bus company information, they have
implemented an IAQ control in the buses. The details are as follows:
With reference to the guidelines from EPD, the
bus company will base on it to monitor the bus air quality. Annually the bus
company will randomly select a lot of buses and perform buses sample testing.
Also, it will conduct a day monitoring to all of them.

Regular bus scientific monitoring results show
that when the ventilation function is activated, the concentration of compartments
pollutants, particularly carbon monoxide and nitrogen oxides, are higher than the time when the ventilation is not
functioning. This finding applies to highways and busy urban road
walking bus line, so it is not preferable
to start the bus ventilation system.

According to the bus company’s sampling results,
the carbon dioxide content of more than eighty percent of buses shows better
result when comparing with the EPA guidelines recommend first-class level. This
level shows that the concentration is below 2.500 ppm hourly in average; the rest
also shows better results than the EPA guidelines recommended second grade
level. This level shows that the concentration is below 3.500 ppm hourly in
average. At the same time, these two results are able to meet the performance
standards recommended by the World Health Organization with the average carbon
dioxide concentration less than 5.000 ppm per eight hours. As a result, air
quality inside buses can be proved to meet the stringent standards of Hong Kong
and the WHO.

Air-conditioned buses will have air
purifiers installed, which performs filtration cycle and purification for air. It can remove fine dust, and kill airborne bacteria and viruses.

Air-conditioning systems, with intelligent
temperature control, automatic adjustment once every four seconds, the car can
automatically adjust the compressor number of horses with the use of inverter
air conditioning system. It can make people feel more comfortable.
Figure 6.1Inside
of Buses
6. Methodology
As mentioned above, three thermal
parameters (air temperature, relative humidity and air velocity) and two
air parameters (carbon monoxide, carbon dioxide) are interested in this
research. A portable instrument “IAQ monitor” is used to measure CO2
concentration, CO concentration, air temperature and relative humidity in each
bus journey. “Vane anemometer” (Brand Name: Velocicalc Plus) is used to measure
the air velocity which is normally used for measuring the low or medium air
speed. The in-bus CO concentration level is recorded to measure air leakage in
passenger compartments. CO2 concentration level serves as the indicator of ventilation sufficiency and odor; while air
temperature, relative humidity and air velocity are measured. Air temperature difference should be measured in the
analysis, with the assumption that passengers would wear clothing dependent
upon the ambient (or seasonal) condition in order to achieve the best thermal
Figure 6.1
IAQ Monitor
The following is
the measuring range and the accuracy for the 5 parameters for these two
equipments. We should know the error and accuracy for the measured data, the
below information is useful for our final justification of the measured data.





Relative Humidity

Air Velocity


– 5000 ppm

– 500 ppm

– 50 ℃

– 95 % RH

.15 – 50 m/s


± 3%

± 3%

± 0.6 ℃

± 3% RH

± 3%

Meanwhile, questionnaire surveys will be
conducted with individual passengers concerning subjective preferences and
dissatisfaction levels towards the in-bus thermal comfort and air quality. The face-to-face survey is concerned with the participants’
subjective responses towards the simultaneous in-bus thermal comfort issues,
measured with the ASHRAE thermal sensation scale.
The survey also includes questions of the sensation votes towards simultaneous
in-bus temperature, humidity, air velocity and the satisfaction of passengers
towards overall thermal comfort. The section concerning the participants’
subjective responses towards the simultaneous in-bus air quality issues had a
5-point-scale voting. Questions are asked about simultaneous in-bus stale air,
stuffy air, dusty air and odor and the satisfaction towards overall in-bus air
quality. Sensation votes towards in-bus thermal comfort, air quality and
combined comfort will be also collected with passengers using a 5-point-scale. Quantifying
the individual subjective sensation responses, they
are relevant to the measured parameters data in the meantime
of conducting each questionnaire. The format of the questionnaire survey is
enclosed as appendix
There are
totally 4 bus routes have been selected in this research which included Kowloon-Hong Kong
Island, Hong Kong Island-New
Territories and New Territories-Kowloon combination. The selection of these 4
routes can mostly cover the different district in Hong Kong. Most of the
measurements are arranged in peak hour (high population in bus) which should be
the worst case for the measurement data. The duration of the bus travelling is
between 30 minutes to 60 minutes and hence the number of samples can be

Possible Deliverable/ Results/Analysis
Since the bus operators have employed a
team of air quality professionals to monitor the concentration of the
pollutants, temperature and relative humidity, I expect most of the measurements
can reach the basic standard of PN-Bus. The target of the bus companies only
focus on the prescribed level rather than to satisfy the passengers’ thermal
comfort and air quality, the questionnaire surveys can actual reflect their
sensation to comparing the measurement of the air and thermal parameters. The
measurements are mostly affected by the time and number of measurements,
population on buses, duration of the bus journey, outdoor air quality, district
for the buses served etc.

7. References

Hammond S.K. (1995).
Pacific Pty, Ltd. Sick Building Syndrome: Cause and Effects. Australia.
(1996). ASHRAE Standard 62-1989R Ventilation for Acceptable Indoor Air
HKASR, Indoor Air Quality information Centre.”>

HKSAR, (1998). Code of Practice for Energy Efficiency of Air Conditioning
& Safety Commission, U.K. (1991). Health & Safety Series Booklet

HS(G)70: The
Control of Legionellosis including Legionnaires’ Disease.

L; Zweers, T; Brunekreef, B; Boleij and Jan S. M. (1990). Sick leave due
to work-related health complaints among office workers in the Netherlands.
A. S., Roberts, K T; Burge, P. S. and Raw, G. (1990). The effect of change
in building ventilation category on sickness absence rates and the
prevalence of sick building syndrome

J; Lindvall, T; Stenberg, B. (1990). Influence of type of ventilation and
outdoor airflow rate on the prevalence of SBS symptoms.

Hong Kong Environmental Protection Department, EPD (2003). Practice Note for
Managing Air Quality in Air-conditioned Public Transport Facilities- Buses.

Hong Kong Environmental Protection Department, EPD.”>Comparison of Hong Kong’s Air Quality Objectives with Air Quality
Standards of the New WHO Guidelines and other Countries.
Sense, (2009). A news release by Green Sense,”>
Notes for the Management of Indoor Air Quality in Offices and Public Places,
Indoor Air Quality Management Group, The Government of the Hong Kong Special
Administrative Region.
(2004). Thermal environmental conditions for human occupancy, ASHRAE Standard
55-2004. Atlanta: American Society of Heating, Refrigerating and
Air-conditioning Engineers, Inc.

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