Plants Volume as a Factor Affecting Outdoor Ambient Air and Thermal Condition

“I hereby declare that I have read this thesis and in my opinion this thesis
is sufficient in terms of scope and quality for the award of the degree of
Master of Engineering (Civil – Environmental Management)”

Signature : ....................................................
Name of Supervisor : ASSOC. PROF. DR. JOHAN SOHAILI
Date : ....................................................

PLANTS VOLUME AS A FACTOR AFFECTING
OUTDOOR AMBIENT AIR AND THERMAL CONDITION

SITI RAHMAH OMAR

A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Engineering (Civil – Environmental Management)

Faculty of Civil Engineering
Universiti Teknologi Malaysia

APRIL 2010

ii

I declare that this thesis entitled “Plants Volume as a Factor Affecting Outdoor
Ambient Air and Thermal Condition “is the result of my own research
except as cited in the references. The thesis has not been accepted for any degree and
is not concurrently submitted in candidature of any other degree.

Signature : ....................................................
Name : SITI RAHMAH OMAR
Date : ....................................................

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To my beloved and respected father, Omar Salleh
My dearly loved mother, Siti Hajar Abas
My brothers;
Mohd Shahir Shamsir
Mohd Shariman Shahril
Mohamad Salehuddin
My sapphire, Md Khairi Mustapa

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ACKNOWLEDGEMENT

In the name of God, the most gracious, the most compassionate, I am grateful
that in preparing this thesis, I was in contact with many people, researchers,
academicians, and practitioners. They have contributed towards my understanding
and thoughts. In particular, I wish to express my sincere appreciation to my
supervisor, Assoc. Prof. Dr. Johan Sohaili, for encouragement, guidance, and critics.
Without the continued support and interest, this thesis would not have been the same
as presented here. I am also indebted to the environmental laboratories technicians for
their support during my survey.

My fellow postgraduate friends should also be recognized for their support.
My sincere appreciation also extends to all my colleagues and others who have
provided assistance at various occasions. Their views and tips are useful indeed. Last
but not least, I am also grateful to all my family members for their patient and love.

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ABSTRACT

This study evaluates the effectiveness of plants for outdoor ambient air and
outdoor thermal improvement based on volume size. The growing conceptualization
of green space is partly as a function that contributing towards a better environmental
quality and maintenance of ecological system in urban area in giving evidence to
sustainable urban living. However, the general requirement for plantings in designated
urban green spaces is 4% from the whole development without reckoning the height
or volume of the plants which should be considered in providing outdoor thermal
comfort and clean air. Focusing on ambient air quality, this study quantify amount of
carbon dioxide, oxygen, temperature and relative humidity influence by plants volume
based on field data. Result shows that there is influence of plants volume in green
space to the pattern of air chemical composition in an outdoor space. The study also
concluded that the design and planning of green space should give more consideration
on both the plants volume and area size especially in a tropical country like Malaysia,
in order to enhance air quality and thermal comfort.

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ABSTRAK

Kajian ini dilakukan bertujuan mengkaji keberkesanan tumbuhan berdasarkan
kepadatan pokok terhadap keadaan udara dan suhu di persekitaraan luar. Konsep
ruang hijau yang semakin menjadi perhatian ramai adalah salah satu faktor yang
menyumbang kepada keadaan persekitaran yang lebih baik dan juga terhadap
kelestarian ekologi di kawasan bandar yang kini semakin pesat membangun. Walau
bagaimanapun, telah dinyatakan bahawa keperluan asas untuk tumbuhan dan tanaman
dalam ruang hijau yang disediakan di kawasan bandar adalah 4% dari keseluruhan
pembangunan itu. Ini tidak mengambil kira ketinggian atau kepadatan tanaman
dimana ia didapati perlu diambil kira untuk memberi kesan terhadap kualiti udara dan
keselesaan suhu di persekitaraan luar. Oleh yang demikian, kajian ini mengenal pasti
jumlah perubahan kandungan karbon dioksida, oksigen, suhu dan kelembapan udara
yang dipengaruhi oleh tumbuhan berdasarkan kepadatan pokok dari kajian lapangan.
Daripada kajian yang dibuat, dapat di rumuskan bahawa jumlah kepadatan pokok
mempengaruhi komposisi udara di kawasan persekitaran luar. Ini menunjukkan
bahawa perancangan dan rekabentuk ruang hijau di kawasan bandar seharusnya
mengambil kira kedua-dua faktor iaitu kepadatan tumbuhan dan juga keluasan
kawasan hijau yg di cadangkan terutama sekali di kawasan beriklim tropika seperti
Malaysia. Ini penting bagi membantu meningkatkan kualiti udara dan suhu yang
menyumbang kepada keadaan persekitaran yang lebih baik dan juga terhadap
kelestarian kawasan bandar.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xiv

1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement 2
1.3 Aim and Objectives 3
1.4 Scope and Limitation 3
1.5 Significant of the Study 4

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2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Natural Atmosphere and Ambient Air 5
2.2.1 Carbon Dioxide 6
2.2.2 Oxygen 8
2.2.3 Temperature and Relative Humidity 9
2.2.4 Wind 10
2.3 Atmospheric Imbalanced and Warming 11
2.4 Urban Context and Environmental Changes 15
2.5 Urban Green Space 16
2.5.1 Types of Urban Green Space 18
2.6 Plants in Urban Area 21
2.6.1 Plants Characteristic 23
2.6.2 Photosynthesis 24
2.6.3 Plant and Carbon 27
2.6.4 Plants and Atmospheric Pollutant 28
2.6.5 Benefits of Plants in Urban Area 29

3 METHODOLOGY 33
3.1 Introduction 33
3.2 Data Collection and Sampling Method 33
3.3 Parameters 36
3.4 Equipments 36
3.5 Method Used to Calculate Plants Volume 37
3.6 Data Analysis 38

4 RESULT AND ANALYSIS 39
4.1 Introduction 39
4.2 Carbon Dioxide 39

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4.2.1 Day and Night Comparison 43
4.2.2 Result from Controlled Environment 45
4.3 Oxygen 45
4.4 Carbon Dioxide and Oxygen 49
4.5 Carbon Dioxide and Temperature 51
4.6 Temperature and Relative Humidity 54

5 CONCLUSION 62
5.1 Conclusion 62
5.2 Recommendation 63

LIST OF REFERENCES 65
APPENDIX 71

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Gaseous mixture surrounding the Earth 6
3.1 Details of courtyard conditions 34
3.2 Details of air-tight glass box conditions 35
4.1 Results shows carbon dioxide differences in various conditions 45
4.2 Results shows temperature differences in various conditions 59
4.3 Results shows relative humidity differences in various conditions 60

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Atmospheric CO2 is essential to most plants and animal life
on earth 7
2.2 Representation of the greenhouse effect 11
2.3 The incoming solar energy that causes the warming or earth
surface in percentage 13
2.4 The absorptivity of various gases as a function of wavelength 14
2.5 New York Central Park. Shows green space is everywhere even
in the biggest city 16
2.6 A densely planted area is highly preferred and provides greater
visual interest than a sparsely planted one 18
2.7 Formation of urban green and greening considerations 19
2.8 Green roof in Fukuoka, Japan 19
2.9 Terrace garden in Prague Castle Garden, Prague 20
2.10 Vertical garden in Huntsville Alabama 20
2.11 Courtyard is surrounded by walls on all four sides 21
2.12 Temperature decrease as plants help cool urban climates through
shading and evapo-transpiration 22
2.13 Evapo-transpiration process influence the outdoor temperature
and relative humidity 23
2.14 Photosynthesis is the conversion of solar energy into chemical
energy, which is stored in sugar 25

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2.15 Midday depression, curve 1, one peaked diurnal course; curve 2,
two-peaked diurnal course; curve 3, one peaked diurnal course
but with severe midday depression 26
2.16 Transfer processes for gaseous and particulate pollutants from
the free atmosphere to terrestrial surfaces 29
2.17 Incorporating plants around buildings can also offer visual
interest and relief to plain walls and roofs and separate them
from the obtrusive hard edges of surrounding buildings. 31
3.1 Plan of the selected green space. The green space selected for
this study is a courtyard which surrounded by school buildings,
and focused only on the ground level 34
3.2 The courtyard conditions were differentiated with four types
of plants volume 35
3.3 The controlled environment conditions were differentiated
with three types of plants volume 36
3.4 The equipment used. From left TSI Carbon Detector, MSA
Altair 4 Multi-Gas Detector, Multi-detector LUTRON 4 in 1,
and Gray Wolf Direct Sense PPC Kit 37
3.5 Methodology for calculating the green volume 38
4.1 Comparison of carbon dioxide concentration according to
different courtyard conditions 40
4.2 Solar intensity in courtyard area changes throughout the day 42
4.3 Different solar intensity during morning and noon 42
4.4 Different solar intensity during evening and night 42
4.5 Comparison of carbon dioxide concentration during day and night 44
4.6 Comparison of oxygen concentration according to different
courtyard conditions 46
4.7 Comparison of oxygen concentration during day and night 48
4.8 Comparison between carbon dioxide and oxygen concentration in
courtyard with grass and plants (C4) 49
4.9 Comparison between carbon dioxide and oxygen concentration in
courtyard with grass only (C3) 50

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4.10 Comparison between carbon dioxide concentration and
temperature deviation in various conditions (C1) no plants
or grass, (C2) plants only, (C3) grass only, (C4) plants and grass 52
4.11 Solar energy reflected by earth surface and absorbed by
vegetation in various conditions (C1) no plants or grass, (C2)
plants only, (C3) grass only, (C4) plants and grass 53
4.12 Comparison between temperature and relative humidity
according to different courtyard conditions 55
4.13 Comparison between temperature and relative humidity during
day and night 58
4.14 Illustration of different box conditions with different solar energy
absorbed by vegetation in (B1) no plants or grass, (B2) plant with
volume, (C3) grass only 60
4.15 Illustration of different box conditions with different transpiration
or evaporative cooling of the plants in (B1) no plants or grass,
(B2) plant with volume, (C3) grass only 61

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LIST OF ABBREVIATIONS

°C - Degree Celsius
CO2 - Carbon Dioxide
H2O - Water
O2 - Oxygen
ppm - Parts per million
RH - Relative Humidity
VOCs - Volatile organic compounds

CHAPTER 1

INTRODUCTION

1.1 Introduction

The world has experienced unprecedented urban growth in the last and current
centuries. Wong and Chen (2009) mentioned that in 1800, only 3 per cent of the
world’s population lived in urban areas and this began to increase significantly after
1900. This rapid urbanization has resulted in environmental changes. According to
Kiran et al. (2004), natural vegetations are usually the first victim of urbanization.
From the ecological point of view, vegetation is important in terms of maintaining an
ecological balance and without them, not only many of the earth’s inhabitants die, but
also the earth itself would suffer.

Changes in urban conditions are also mentioned to have often caused
deterioration in environmental quality and may result in damage to the health of city-
dwellers (Wilhelm, 2008). One of the alarming concerns is the degradation of
ambient air quality. The urban building and economic activity result in pollution and
warming of the air. Thus, in term of preventive or protective environmental actions,
Wilhelm (2008) mentioned that one of the methods is to increase size of urban parks
and green space as well as using plants on both vertical and horizontal surfaces since
plants have proved their resistance to urban environmental stress.

Consequently, this shows that urban area and cities needs green spaces such as
park and garden. Herbert (2002) mentioned that if cities were compared to organisms,

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parks and garden situated within it acts as the ‘green lungs’. This is because creation
of green spaces, especially with trees and vegetation could promote in human and
urban ecology well being. Therefore, proposed green spaces were considered as
essential ‘breathing spaces’ within the built environment (Peter, 2006), because of the
plants activities which enhanced the balanced conditions of the atmosphere.

Currently, green spaces in Malaysian urban area are usually proposed and
reserved 10% from the whole development area (Jabatan Landskap Negara, 2008).
This artificial formation of green spaces is usually planned and landscaped in the
process of urbanization. Wong and Chen (2009) stressed that, the artificial formation
of green space is the windows and links from which the urban dwellers can access
Mother Nature in the harsh built environment. Passive interaction with nature and
plants in urban green space has also been associated with many beneficial responses,
including reductions in stress, improvements in health, and restoration from mental
fatigue. Thus shows plants play a major role in providing better urban environment as
well as human and urban ecology well being.

1.2 Problem Statement

The benefits of greening the urban area have been taken for granted
when it is emphasized on the basis of design and planning alone. Wong and Chen
(2009) stated that there are two omitted yet significant concerns which may need
scientific input; how many plants should be introduced and how much the
environment will respond.
The proposed plants in urban green space are also usually small and
have less volume compared to the existing mature plants which usually being torn
down during the site clearance for new development. Even though new plantings will
be planted again, the significant size different did affect the urban outdoor
surroundings and urban ecology well being. Furthermore, the formations of green area
which are proposed and designed did not truly consider the amount of plantings and
its dense value in improving the outdoor environment. Thus shows that, the outdoor

3

plantings and urban green space need to be consider quantitatively and supported the
environmental balanced and physical needs in regards with ambient air and thermal
condition.

1.3 Aim and Objectives

The aim of the study is to determine the effect of plants in volume size on
outdoor ambient air and thermal conditions. The objectives of this study are as the
followings:

(i) To determine the changes of carbon dioxide, oxygen, temperature and
relative humidity according to various plants volume allocation.

(ii) To identify capability of plants in volume size upon improving outdoor
ambient air and thermal improvement.

1.4 Scope and Limitation

Vegetation always accompanies the growth of cities in different formations. It
is rare to have natural formation of aboriginal plants in an urban environment due to
the constraint of space. This study will select the artificial formation of green area
which also known as green space. Parks, garden, courtyard, green roofs, green walls
or terraces are all artificial formations which are planned and landscaped in the
process of urbanization. Thus, this study will focus only on courtyard which is one of
the artificial formations of green space in urban area. The plants selection for this
study will be ornamental plants or low shrubs. This is because large plants or trees
gives shade and this could not justify the plants volume capability in improving
outdoor ambient air and thermal improvement.

4

However, the study will not deal with the species and arrangement of planting
as well as the design and usage style. This is because, in term of design and aesthetic,
what each person needs is different and Wayne (1995) mentioned that the ideal
environment should be able to respond to human being preference for air quantity,
quality, temperature and humidity.

1.5 Significance of the Study

Currently, there is a need in quantitative input on how many plants should be
introduced and how much the environment will respond (Wong and Chen, 2009). In
Malaysia, Jabatan Landskap Negara (2008) stated that the green space in urban area
should consist minimum 40% of soft landscape. However this 40% is basically total
covered area of greenery without reckoning the size, height or volume of the plants.

The proposed plantings and vegetation in urban area should be considered
quantitatively as to provide and support the urban environment balanced and physical
needs. In this context it can be argued that the role of green space as an environmental
aid in urban area necessitates an evaluation of plants quantity required in the green
space in regards to air quality and thermal conditions. The evaluation will provide
understanding on plants in volume size effect to the outdoor ambient and will
hopefully benefits towards a better outdoor urban green space.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter discussed on natural ambient air, urban context and
environmental changes as well as urban green space and plants within it. It is focused
on the outlined as well as related topics and was based on the needs to understand the
attributes and insight into the possible outcome throughout the study. This is also for
further understanding in the study topics, provides information to support the study’s
result along with its applied approach towards a better outdoor urban environment.

2.2 Natural Atmosphere and Ambient Air

The atmosphere is essential to life (Speight and Lee, 2000). The natural
atmosphere is seldom thought of as harmful or damaging, nevertheless, within the
atmosphere exist great treats to all life. In its present state, the consequences of
changes could be more severe, therefore it is important to understand the natural
atmosphere and consider our effects upon it.

Atmospheric variable include gaseous mixture, temperature and water vapour.
It is clear that the atmosphere provides the air we breathe. Humans normally can only
survive for about three to four minutes without air. For this reason, it is the single

6

most important resource we have. Williams (2004) stated that all the other
environmental concerns attach into the preservation of our atmosphere.

Natural ambient air is a gaseous mixture surrounding the Earth atmosphere
which consists of different gasses such as shown in table 2.1.

Table 2.1: Gaseous mixture surrounding the Earth
Gases Percentage
Nitrogen 78%
Oxygen 21%
Carbon Dioxide 0.03%
Inert Gases 0.97%

In addition, air has no colour, taste or smell and also contains dust particles
and microorganisms. Shown on Table 2.1, Oxygen has 21% of the gaseous mixture
surrounding the Earth. Based on several references, it indicates that Oxygen makes up
20% to 21% of the Earth’s atmosphere (Treshow and Anderson, 1989; Williams,
2004; Ong et al. 2004; Godish, 2004). However Vesilind and Morgan (2004)
mentioned that such air composition is not found in nature and is of interest only as
reference.

2.2.1 Carbon Dioxide

Atmospheric carbon dioxide (CO2) is essential to most present day plant and
animal life on earth because it provides the carbon input to photosynthesis (Figure
2.1). However, the significant release of CO2 into the atmosphere caused air
degradation and imbalance resulting from activities such as the combustion of fossil
fuels and changes in land use especially deforestation that constitute the primary
detectable human influence on global climate (Runeckles, 2003).

7

Some of the carbon dioxide removed from the atmosphere by photosynthesis
and some will absorb by the ocean enough to restore equilibrium or atmospheric
balance (Treshow and Anderson, 1989). Now that CO2 is building up in the
atmosphere, further actions should be taken. Adding to our concern is that the forests
are being destroyed and this is a highly concerned matter since the trees and plants act
as sinks or buffer for our carbon dioxide.

Figure 2.1: Atmospheric CO2 is essential to most plants and animal life
on earth (Williams, 2004)

Furthermore, carbon dioxide imbalanced is expected to rise and increase the
mean global temperature by 1.1°C to 4.5°C. Jonathan (2003), Runeckles (2003), and
Al Gore (2006) discussed that there is interrelationship between temperature and

8

atmospheric CO2 concentration within earth’s complex land-ocean-atmosphere
system. It indicates that when there is more CO2 in the atmosphere, the temperature
increases. Thus shows that CO2 is thought to be dominating the heating up of the
world due to the increased greenhouse effect.

2.2.2 Oxygen

As stated by Speight and Lee (2000), the atmosphere is the source of oxygen
(O2) for respiration. Atmospheric oxygen is also utilized by aerobic organisms in the
degradation of organic material. As one would expect the oxygen concentration in the
atmosphere is slowly declining if plants and fossil fuel carbon is being burned to give
CO2. Although the amount of oxygen in the atmosphere is deteriorating, Jonathan
(2003) stated that there is plenty left for us to breathe. The total amount that has been
lost in the last 200 years is much less than one-thousandth of the oxygen in the
atmosphere.

Fishman (1990) stated that ozone (O3) forms readily in the stratosphere as
incoming ultraviolet radiation breaks molecular oxygen (two atoms) into atomic
oxygen (a single atom). In that process, oxygen absorbs much of the ultraviolet
radiation and prevents it from reaching the Earth’s surface where we live. He also
mentioned four simplified chemical formula as the explained below.

O2 + sunlight O + O (2.1)

When an electrically excited free oxygen atom encounters an oxygen
molecule, they may bond to form ozone.

O + O2 O3 (2.2)

Destruction of ozone in the stratosphere takes place as quickly as formation of
ozone, because the chemical is so reactive. Sunlight can readily split ozone into an
oxygen molecule and an individual oxygen atom.

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O3 + sunlight O2 + O (2.3)

When an electronically excited oxygen atom encounters an ozone molecule,
they may combine to form two molecules of oxygen.

O + O3 O2 + O2 (2.4)

The ozone formation-destruction process in the stratosphere occurs rapidly
and constantly, maintaining an ozone layer.

The evolution of free atmospheric oxygen at elevated concentrations set the
stage for the evolution of oxidative metabolism, the series of energy-transferring
chemical reactions that sustain most life forms. Oxygen, as consequence, is vital to
almost all living things.

2.2.3 Temperature and Relative Humidity

Relative humidity is the relationship between the air temperature and the
amount of water vapour it contains. On the other hand, humidity is the amount of
water vapour in the air. When it has been raining and the air is saturated, there is 99 to
100 percent humidity. Relative humidity is expressed in percent and this can be
written as an equation (2.5). Godish (2004) explained that it is the percent of air (H2O
vapour a volume) holds at a given temperature. Since air can hold more H2O vapour
at higher temperatures, relative humidity values decrease as temperature increases.

water vapour present in the air X 100%
RH = (2.5)
water vapour required to saturate air
at that temperature

The tropical climate in Malaysia is hot and humid. Hussein and Rahman
(2009) explained that data obtained by the Malaysian Meteorological Service for ten-

10

year period records the outdoor temperatures are relatively uniform. The average
temperatures between 23.7ºC to 31.3ºC throughout a day with the highest maximum
recorded as 36.9ºC and the average relative humidity throughout a day is between
67% to 95%. The reason for the high temperature and high relative humidity is it will
reduce the rate of evaporation of moisture from human body, especially in the
locations where the lack of air movement is experienced (Wong and Chen, 2009).

According to Laurie (1979), when it is desirable to increase humidity, trees
can be a valuable mechanism for moderating urban microclimate. This is because as
water is released through plants’ stomata, it evaporates into atmosphere. As
evaporation takes place atmospheric moisture content or humidity is increased. Thus
this is important because Laurie (1979) also stated that the control of urban
microclimates and temperature is related to the control of humidity as well as solar
radiation and wind.

2.2.4 Wind

Wind is important as a natural cooling strategy in the tropics. Wind as
mentioned by Williams (2004) is a product of atmospheric air pressure that is caused
by unequal heating of the Earth’s surface. Pressure differences cause air to move.
Like fluids, air flows from areas of high pressure to areas of low pressure. Wind as
mentioned by Godish (2004) is the term commonly used to describe air movement in
the horizontal dimension. As mentioned by Yabuki (2004), wind is considered as
environmental factors for plants growth and it effect the gasses exchange between air
and plants.

For outdoor environment, the effect of wind is more complicated as it is often
inter-related with solar exposure. A review of outdoor thermal comfort studies (Cheng
and Ng, 2008) has showed that at air temperature of about 28°C, the comfort wind
speed for a pedestrian in shade could vary from 0 to 3 m/s. Therefore a high wind

11

speed is needed to compensate for the high temperature in order to achieve thermal
comfort.

Wind not only moves the pollutants horizontally, but it causes the pollutants to
disperse (Speight and Lee, 2000), reducing the concentration of the pollutant with
distance away from the source. According to Vesilind and Morgan (2004), the amount
of dispersion is directly related to the stability of the air, or how much vertical air
movement is taking place. Thus shows that in wind is considered as one of the
important factor in the atmosphere.

2.3 Atmospheric Imbalanced and Warming

According to Davis and Masten (2004), the atmosphere is somewhat like
engine. It is continually expanding and compressing gases, exchanging heat, and
generally creating chaos. The change in the element of the atmosphere is the tendency
for the temperature close to the earth’s surface to rise. This is a phenomenon referred
as the greenhouse effect (Speight and Lee, 2000). This term is used to describe the
warming or rise in the temperature of the earth when the energy from the sun is
trapped and cannot escape from the enclosed space as shown in figure 2.2.

Absorbed Atmosphere

Atmospheric Radiation from
Processes the Earth
Reflected Absorbed
Surface
Subsurface

Figure 2.2: Representation of the greenhouse effect (Speight and Lee, 2000)

12

Furthermore, the atmospheric imbalanced usually caused by pollution.
According to Godish (2004) the concept of pollution includes a sense of degradation,
a loss of quality, a departure from purity, and adverse environmental effects. He also
mentioned that air becomes polluted when it is changed by the introduction of gases
or particulate substances or energy forms so that the locally, regionally, or globally
altered atmosphere poses harm to humans, biological systems, materials, or the
atmosphere itself.

Levels of pollution experienced by cities and buildings can be greatly
influenced by location, morphology and the local climate (Susan et al., 2004).
Moreover, indoor air pollution is stated linked with the outdoor air pollution or
ambient air pollution that occurs in both urban and rural areas.

One of the important factors of atmospheric warming is the Sun which is the
ultimate energy source for all atmospheric processes (Bhatti et al., 2006). Solar
radiation is also the main energy input factor that determines plants growth and
production. Heat, ultimately derived from solar radiation, can be transferred to the
atmosphere in four different ways (Treshow and Anderson, 1989). First is by
conduction, secondly is by convection where air is warmer near the ground, causing it
to expend and rise. A third way by which heat transferred to the atmosphere is by
means of evaporation. Finally is the thermal radiation.

Visible light is partly thermal radiation. The atmosphere reflects scatters and
absorbs some of the solar radiation that passes through it. Thus shows that the
atmosphere already exhibits a greenhouse effect by absorbing some of the outgoing
thermal radiation and warning the earth. Furthermore, warming of the earth also due
to soil temperatures under sealed surfaces are clearly higher than the average and in
the urban area, heat island may develop.

Figure 2.3 shows that the 51% of solar energy warming the Earth surface, 30%
carried up by conduction & convection, 6% transmitted directly out to space from
surface radiation, and the final 15% as surface radiation which is absorbed by the
atmosphere & clouds before being radiated out to space. 29.4% of the energy radiated

13

from the Earth's surface is absorbed by the atmosphere.70.6% of the energy heats the
atmosphere by other means. Of the 29.4%, a tiny portion will be in the absorption
band of CO2.

Figure 2.3: The incoming solar energy that causes the warming or earth surface in
percentage (Kusterer, 2007).

According to Kusterer (2007) part of the solar energy that comes to Earth is
reflected back out to space in the same, short wavelengths in which it came to Earth.
He also explained that the percentage of solar energy that is reflected back to space is
called the albedo. Different surfaces have different albedos. Over the whole surface of
the Earth, about 30 percent of incoming solar energy is reflected back to space. Ocean
surfaces (26% albedo) and rain forests (15% albedo) reflect only a small portion of
the Sun's energy. Deserts however, have high albedos (40%); they reflect a large
portion of the Sun's energy. Thus shows that forest absorbs the solar energy which
helps reduce heat and temperature. Even if the greenhouse gases traps the heat from
earth, by increasing vegetation area the energy from sun will be used accordingly.

14

Unfortunately, the problem faced by the world today is the additional warming
that is being produced by several natural anthropogenic gases that being injected into
the global atmosphere by human activities and urbanization. Treshow and Anderson
(1989), stresses that we are not only facing a greenhouse effect, but super-greenhouse
effect due to both natural and additional warming.

It is also important to understand that various gases that made up Earth
atmosphere absorbs heat energy at specific wavelengths. Figure 2.4 shows the
absorptivity of various gases as a function of wavelength (Vesilind and Morgan,
2004). Carbon dioxide absorbs almost none of the sunlight coming to Earth because
its absorptive effect is most pronounced at wavelengths greater than about 1.5µm,
missing most of the sunlight spectrum. Looking at the right side of the Figure 2.4
however, it is clear that carbon dioxide can be effective energy absorber at the
frequencies normal to heat radiation from earth.

Figure 2.4: The absorptivity of various gases as a function of wavelength
(Vesilind and Morgan, 2004).

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2.4 Urban Context and Environmental Changes

The world has experience unprecedented urban growth. In the last and
current centuries has lead to rapid urbanization and for the past two centuries resulted
in significant environmental changes (Wong and Chen, 2009). Changes in urban
conditions are also mentioned to have caused deterioration in environmental quality
and cause damage to the health of urban-dwellers (Wilhelm, 2008). One of the
alarming concerns is the degradation of air quality. The urban building and economic
activity also result in pollution and warming of the air. Furthermore, the change of
urban climate, especially micro-climate, is definitely associated with the rapid
urbanization. Higher temperature in urban areas means hazards of thermal discomfort,
air pollution and even water pollution. Furthermore, natural elements including the
fresh air, light and green scenery which help promoting health restoration (Burnett,
1997) might be jeopardize due to rapid changes in urban conditions.

Urban modification of the atmospheric environment can occur by the
replacement of the natural surface of soil, grass, and plants by the multiplicity of
urban surfaces of brick, concrete, glass, and metal at different ground. According to
Berry (1990), these artificial materials change the nature of the reflecting and
radiating surfaces, the heat exchange near the surface, and the aerodynamic roughness
of the surface. Since hard surfaces predominate in urban areas, during periods of
intense incoming radiation, the temperature are likely to be higher in urban area than
in the suburbs or countryside. Laurie (1979) stated that particularly in the central areas
of large urban development, this can be result in temperatures being raised by 4°C to
6°C, occasionally by as much as 10°C.

There are several factors that determine the thermal build up in urban area.
Firstly is the large conductivity and heat-storage capacity of most building fabrics
compared with natural soils. This promotes the twin processes of heat storage during
the day and subsequent release of the stored heat at night. Furthermore, the input of
energy from artificial sources and the contribution made by solar radiation, lead to the
high proportion of pollutants in the atmosphere above towns compared to the open
countryside.

16

Moreover, the pollution level in the urban atmosphere still frequently remains
above the limits normally considered to be safe for human (Laurie, 1979). Thus, in
term of preventive or protective environmental actions, Wilhelm (2008) mentioned
that one of the methods is to increase size of urban parks and green space as well as
using plants on both vertical and horizontal surfaces. Wong and Chen (2009) also
suggested that vegetation should be introduced extensively yet carefully in urban area.

2.5 Urban Green Space

Urban green spaces are recognized as important ecosystem in urban and
suburban area (Peter, 2006). Green space of course is not always perfectly green, and
it is everywhere even in the biggest city (Figure 2.5). The purpose of proposing urban
green space is not only because plants are the aborigines which should be preserved,
but also because their broader benefits cannot be produced by any other life-form.
Peter (2006) also claimed that the growing conceptualization of green space in all its
complexity is partly a function of lobbying for better environmental quality and
maintenance of ecological systems in urban area.

Figure 2.5: New York Central Park. Shows green space is everywhere
even in the biggest city

17

Consequently, this shows that urban area and cities needs green spaces such as
park and garden. According to Laurie (1979), urban green space could be considered
as a place that functions as an enrichment of the environment, for intimacy of
character and for modification of the climate. Herbert (2002) mentioned that if cities
were compared to organisms; parks and garden situated within it acts as the ‘green
lungs’. This is because creation of green spaces, especially with trees could promote
in human and urban ecology well being. Therefore, proposed green spaces were
considered as essential ‘breathing spaces’ within the built environment (Peter, 2006).

The green spaces in urban area are planned and landscaped. This artificial
formation is simply the compromise to rapid urbanization. As a precious resource, it
is the windows and links, from which the urban dwellers can access Mother Nature in
the harsh built environment (Wong and Chen, 2009). Ulrich (1981) found that scenes
of natural environments have more positive influence on human emotional states.

Moreover, the outdoor environment or green space as mentioned by Said et
al., (2004) is known to have restorative power. It is because man recognises the
physical and symbolic benefits of plants, fresh air, sunlight and scenic views for more
than one thousand years ago. Currently, green spaces in Malaysian urban area are
usually proposed and reserved 10% from the whole development area, and from this
10%, it should consist minimum 40% of soft landscape or plantings (Jabatan
Landskap Negara, 2008). Even if it lack of detailed indicator of plants quantity and
quality that should be chosen and proposed, this guideline helps in promoting more
greenery in the buildup area.

People and urban dweller enjoy contact with nature; however it is not enough
simply to plant a few trees and set down a bench or two. For instance, according to
Carpman and Grant (1993) a densely planted area such as shown in Figure 2.6 is
highly preferred and provides greater visual interest than a sparsely planted one. They
also pointed out that there are findings shows that scenes with greater number of trees
were consistently rated higher than those with fewer trees. Thus shows that plants
play a major role in the urban green space.

18

Figure 2.6: A densely planted area is highly preferred and provides greater visual
interest than a sparsely planted one

2.5.1 Types of Urban Green Space

Owing to its importance, vegetation always accompanies the growth of cities
in different formations. The formation of plants, according to Wong and Chen (2009)
can be roughly divided into two major categories. Figure 2.7 shows that the two major
categories are natural and artificial. It is rare to have natural formation of aboriginal
plants in an urban environment due to the constraint of space. Parks, garden,
courtyard, green roofs, green walls or terraces are all artificial formations which are
planned and landscaped in the process of urbanization. Figure 2.7 also shows that
artificial formation can be further divided into two groups. One is landscaping on the
ground which fills in the public areas in urban environment for example parks,
courtyard and garden. The other group under artificial formations is landscaping on
buildings. This includes rooftop gardens or green roof (Figure 2.8), terrace gardens
(Figure 2.9) and vertical landscaping (Figure 2.10).

19

Urban Green

Natural formation Artificial formation

Natural reserve

Landscape on the ground Landscape on buildings

City Park Rooftop garden

Courtyard Balcony garden

Other green areas Vertical landscaping

Figure 2.7: Formation of urban green and greening considerations (Wong and Chen, 2009)

Figure 2.8: Green roof in Fukuoka, Japan

20

Figure 2.9: Terrace garden in Prague Castle Garden, Prague

Figure 2.10: Vertical garden in Huntsville Alabama

21

Courtyard as shown in figure 2.11 which is the focus of this study is a type of
green space surrounded by walls on all four sides and may be located on grade or on a
roof. However, it is important to note that the artificial formation should never be
viewed as a satisfactory alternative to losing nature which should be preserved at all
costs.

Figure 2.11: Courtyard is surrounded by walls on all four sides

2.6 Plants in Urban Area

Plants in an urban are mentioned to be able to provide benefits in the form of
environmental, social, financial and aesthetic value (Wong and Chen, 2009).
Furthermore, it provide many valuable ecosystem services: they reduce energy
consumption, trap and filter storm water, help clean the air by intercepting air
pollutants, as well as help in the fight against global climate change by sequestering
carbon dioxide (Kelaine et al., 2008).

Jonathan (2003) mentioned that plants have likely had a big influence on CO2
level in atmosphere. They were the main source of oxygen, as it is one of the products

22

of photosynthesis and acted as a trap for carbon. It is also mentioned that the bigger
land plants, have likely led to a further increase in CO2 uptake.

Plants also absorb gaseous pollutants for example nitrogen dioxide, and
sulphur dioxide through leaf surfaces, intercept dust, ash, pollen, and smoke, release
oxygen through photosynthesis, reduces emissions of pollutants from power plants
including volatile organic compounds (VOCs), as well as give shades which lowers
air temperatures, reducing hydrocarbon emissions and CO2 levels (Wilhelim, 2008).

Figure 2.12: Temperature decrease as plants help cool urban climates through shading and
evapo-transpiration (Wilhelim, 2008)

Plants can offer cooling benefits in a city through two mechanisms, direct
shading and evapo-transpiration. Figure 2.12 shows that temperature is lower in the
area with dense plantings. According to Wong and Chen (2009), the shading effect is
quite straightforward and it very much depends on the density of plants. People
normally have no quantitative sense of plants’ evaporative ability. The temperature
reduction can benefit individual building as well as the urban environment.

Plants absorb water through their roots and emit it through their leaves, and
this movement of water is called transpiration. A large tree can transpire 40,000
gallons of water per year; an acre of corn can transpire 3,000 to 4,000 gallons a day
(Wong et al., 2006). Evaporation, the conversion of water from a liquid to a gas, also
occurs from the soil around vegetation and from plants as they intercept rainfall on
leaves and other surfaces. Together, these processes are referred to as evapo-
transpiration.

23

Evapo-transpiration cools the air by using heat from the air to evaporate water.
Evapo-transpiration, alone or in combination with shading, can help reduce air
temperatures. Figure 2.13 shows plants take water from the ground through their roots
and emit it through their leaves, a process known as transpiration. Water can also
evaporate from tree surfaces, such as the stalk, or surrounding soil.

Figure 2.13: Evapo-transpiration process influence
the outdoor temperature and relative humidity
(Williams, 2004)

2.6.1 Plants Characteristic

There are more than 200,000 different kinds of vascular plants and not any
species can be considered truly typical (Treshow and Anderson, 1989). The most
familiar include the coniferous and deciduous trees, shrubs, vines and grasses. The
generalized plant structure consists of root and shoots which made up of the stem and
leaves. Leaf is the principal photosynthetic organ of the plant and mostly has a
pigment called chlorophyll. Plants also have stomata. A stoma is a pore, found in the
leaf and stem epidermis that is used for gas exchange.

24

It is clear that plants need sunlight, water and CO2 to do photosynthesis.
However, the changes of atmospheric CO2 concentration and temperature will have
important consequences to plants. According to Jonathan (2003), plants usually
prevent themselves from losing too much water in the drying air, but they also need to
take in CO2 in order to photosynthesize. A plant could easily coated themselves with
waxy layer to prevent water lost however this would almost totally prevent CO2 from
getting into its leaves, and it would be unable to grow. Therefore plants have to
balance of between gathering CO2 in order to photosynthesize and avoiding death by
dehydration. Jonathan (2003) explained that when plants have plenty of water, the
stomata let CO2 in. If more water added around the roots of the plants, they will take
up more CO2 and photosynthesize. If instead more CO2 added to the air around the
plants, very often they do the opposite.

During the growth process of plants, carbon is being sequestered. Therefore,
this shows that growing more trees and plants could mitigate climate change through
carbon sequestration. Unfortunately this solution is not that simple. Plants and trees
normally grow slowly. Although the potential to sequester carbon is fairly large, the
actual carbon sequestration rate on annual basis is rather small (Bhatti et al., 2006).
However it is mentioned that plants and trees having thick canopies and dense foliage
provide the most benefits (Laurie, 1979).

2.6.2 Photosynthesis

The only natural mechanism known to utilize atmospheric CO2 is
photosynthesis by green plants. Photosynthesis is the conversion of solar energy into
chemical energy, which is stored in sugar. The chemical reaction that takes place in
simplified form is as below. It shows that water, carbon dioxide and solar energy are
converted into glucose and oxygen.

6H2O + 6CO2 + sunlight C6H12O6 + 6O2 (2.6)

25

The photosynthesis process creates carbohydrates that are distributed to the
various plant components, resulting in the growth of plants attributes. Without
photosynthesis there would be no animal life, no oxygen in our atmosphere, no fossil
fuel reserves and according to Treshow and Anderson (1989) it would perhaps did not
have any free water due to excessive heat trapped because of the greenhouse effect.

Figure 2.14: Photosynthesis is the conversion of solar energy
into chemical energy, which is stored in sugar (Williams, 2004)

Photosynthesis occurs in the chloroplasts, which are located in the cells of a
plant leaf (Figure 2.14). It is performed in two separate reactions: light reactions and
dark reactions. The light reactions occur during the day. When light strikes a pigment
called chlorophyll, electronic energy is excited and manipulated in a chemical process
called photophosphorylation, where energy is produced in the form of adenosine
triphosphate (ATP). This ATP produced by the light reactions fuel the synthesis of
glucose (sugars), which is accomplished during the dark reactions. Through a
chemical process called the Calvin cycle, carbon dioxide is harvested and manipulated
to produce glucose molecules (Mohammad, 1997).

26

According to Xu and Shen (1997), midday depression of photosynthesis
occurs in many plants. It is a common phenomenon. Xu and Shen (1997) mentioned
that under natural conditions there are two typical patterns of photosynthetic diurnal
course (Figure 2.15). One is one-peaked which net photosynthetic rate increase
gradually with the increase in sunlight intensity in the morning, reaches its maximum
around noon, and then decreases gradually with the decrease in sunlight intensity in
the afternoon. Another in two-peaked where there are two peak values of net
photosynthetic rate, one in late morning and another in late afternoon with a
depression around noon.

Figure 2.15: Midday depression, curve 1, one peaked diurnal course;
curve 2, two-peaked diurnal course; curve 3, one peaked diurnal course
but with severe midday depression (Xu and Shen, 1997)

Ecological factors responsible for midday depression are sunlight, air
temperature, air humidity, soil water status and carbon dioxide concentration in the
air. In general, the two-peaked diurnal course of photosynthesis occurs on clear day
with intense sunlight, while the one-peaked diurnal course occurs on cloudy days with

27

weak sunlight (Xu and Shen, 1997). Naturally, it is assumed that the midday
depression is caused by intense light.

To some extent midday depression is related to high air temperature because
of enhanced CO2 efflux from respiration and/or photorespiration. Midday depression
of photosynthesis is also often accompanied by a decreased CO2 concentration around
noon (Xu and Shen, 1997). Decreased CO2 concentration is an important ecological
factor leading to midday depression.

2.6.3 Plants and Carbon Dioxide

Plants excel at storing carbon. As a consequence, the photosynthesis process
in which ambient CO2 is used to create sugars and carbohydrates, plants sequester
carbon (Bhatti et al., 2006). Because of these unique characteristic, plants are the
main living organisms on Earth that have the capacity to mitigate the increase in CO2
concentration in the atmosphere.

Over 99% of the carbon in living organisms on earth is held within plants
(Jonathan, 2003). In the 1980s, ecologist began to consider on how fast forests take up
carbon. This relied on taking comprehensive measurements of the CO2 concentration
around the trees. The idea is that if a forest is photosynthesizing and using up CO2,
this would show up as a depletion of CO2 in the air adjacent to the forest. Even though
the forest ecosystem is also respiring during the day, in daytime there will normally
be more photosynthetic uptake of carbon than carbon release from respiration.
Followed by night-time assessment to measure how much the CO2 concentration
around the forest has been raised at night relative to the background level in the
atmosphere (Jonathan, 2003).

However, it is mentioned that this approach is compelling but also very
ambitious. Various studies show strange result and there is nagging question of
whether these studies might contain errors. It is pointed out that a lot of important

28

processes occur in forest such as tree falls, landslides and droughts which might affect
the data. Even though it remains an open question as to how much it can really teach
us, it is nevertheless scientifically important.

2.6.4 Plants and Atmospheric Pollutant

Atmospheric pollutants are transported to vegetation from their source by
wind and turbulence (Fowler, 2003). Wind spread pollutants over landscape and
transport pollutions from sources and source area. The transport of gases from the
atmosphere to the terrestrial surfaces is by turbulent transfer, which is generated by
frictional drag by terrestrial surfaces on the wind. Thus the nature of the surface
strongly influences rates of transfer.

Fowler (2003) mentioned that the aerodynamically rough surfaces of forests
and woodland generate much greater frictional drag on air flow and as a consequence,
rates of transport of pollutants from the free atmosphere to the surface are much
greater over forests than over short vegetation for example grassland. Figure 2.16
shows that the rates of deposition of pollutant gases and particle depend on both the
turbulent transfer to the surface and processes at the surface which determine the
uptake of gases or capture of particles.

According to William (1990), plants in general have the function as sinks for
gaseous pollutant. The gases transferred from the atmosphere to vegetation by the
combined forces of diffusion and flowing air movement. Once in contact with plants
gases may be bound or dissolved on exterior surfaces or be taken up by plants via
stomata. Thus shows that plants have the capability not only to enhance the urban
atmosphere but also act as a functional companion that acts on pollutant towards a
better urban living.

29

Grass / Vegetation

Figure 2.16: Transfer processes for gaseous and particulate pollutants from the
free atmosphere to terrestrial surfaces (Fowler, 2003)

2.6.5 Benefits of Plants in Urban Area

It is mentioned by Wong and Chen (2009) that plants in urban area can
provide quantitative benefits, in the form of financial returns, as well as qualitative
environmental, social and aesthetic benefits.

a) Environmental Benefits

Plants offer cooling benefits in an urban area through two mechanisms, direct
shading and evapo-transpiration which has been explained earlier. As a result, not
only shaded hard surfaces in the urban area but also the ambience can experiences
relatively low temperatures. The temperature reduction can benefit not only individual
buildings but also the urban environment. Furthermore, plants have been widely
believed to be effective scavengers of both gaseous and particulate pollutants from the
atmosphere in the urban environment (Miller, 1997). They can improve the air quality
by filtering out airborne particles in their leaves and branches as well as by absorbing
gaseous pollutants. The low surface temperature caused by plants may also reduce the
risk of forming low atmospheric ozone which is the primary component of smog.

30

However, vegetation does not always respond positively to pollution stress.
Air pollution has a negative impact on plant metabolism. A reduction of
photosynthetic capacity or even the appearance of chlorosis or necrosis can be
observed in plants which are planted in a heavily polluted environment (Coleman et
al., 1995). Planted surface has the ability to retain storm water and it is a practical
technique for controlling runoff in a built environment. Environmentally, this translate
into benefits such as reduction of the surface contaminants in the rainwater, reduced
occurrence of soil erosion and improved well-being for aquatic animals and plants.

b) Economic Benefits

Economic benefits are very much related with the environmental benefits
brought by plants in an urban area. The ability of surface covered with vegetation to
retain storm water and lower peak runoff can help in reducing the extent of storm
water drainage infrastructure. This has been applied by employing smaller storm
sewers, which in turn saves construction and maintenance costs of the town’s
drainage systems. Plants introduced around buildings can improve construction’s
integrity by lessening the weather effect (Wong and Chen, 2009).

Energy saving are another significant economic contribution brought by plants
in the urban area. Not only tree shading but also strategically placed plants around
buildings can achieve energy savings. In Singapore, a hospital has managed to cut its
water and electricity bills by SGD800, 000 in one year after adopting green roofs and
other environmental considerations (Nathan, 1999).

c) Aesthetic Benefits

Landscaping has often used to improve the aesthetic of the urban environment.
The support for the preservation of plants has been attributed to the attraction that
many urban dwellers feel for the natural landscape. Vegetation can provide visual
contrast and relief from a highly built-up city environment. Plants also give a
significant psychological sense of accessing Mother Nature in concrete jungles where

31

buildings and pavements dominate the urban area. Furthermore, vegetation provides
elements of natural scale and visual beauty. In addition, incorporating plants around
buildings can also offer visual interest and relief to plain walls and roofs and separate
them from the obtrusive hard edges of surrounding buildings (Figure 2.17). Unsightly
building systems can also be hidden by vegetation on the rooftops and facades.

Figure 2.17: Incorporating plants around buildings can also offer visual interest
and relief to plain walls and roofs and separate them from the obtrusive hard edges
of surrounding buildings

d) Social Benefits

Plants can fulfil various social functions in a built environment. Green space
in urban area provide places for playing, sport and recreation, meeting, establishing
social contacts, isolation and escape from urban life, as well as aesthetic enjoyment.
There is no doubt that trees and plants in parks help in creating a sense of community

32

in the neighbourhood (Wong and Chen, 2009). Urban area can be made livelier by
providing ample amounts of accessible outdoor recreation or amenity space.

It has also been proved that visual and physical contact with plants can result
in direct health benefits. Ulrich and Parsons (1992) studied the psychological effects
of plants on humans and revealed that plants can generate restorative effects leading
to decreased stress, improve patient recovery rates and higher resistance to illness.
Besides their psychological impacts, plants have other physical impacts which
benefits human. The air cleansing quality of plants has direct respiratory benefits for
people who suffer from asthma and other breathing ailments, and directly lowers
smog and other forms of air pollution. The potential of greenery to lower high
temperature can reduce heat-aggravated illness, which directly and indirectly reduce
life expectancy of human beings and death among the city population.

CHAPTER 3

METHODOLOGY

3.1 Introduction

This chapter explained thoroughly the procedure of works as to achieve the
aim and objectives of this study. Detailed processes and method are illustrated which
focus on types of data collection, types of equipment used during data collection, and
methods used to calculate plants volume.

3.2 Data Collection and Sampling Method

Data collection is taken during clear sunny day and was collected in two
categories. In the first category, data collection is done in a green space. The green
space selected for this study is a courtyard and focused only on the ground level
(Figure 3.1). Courtyard as mentioned earlier is a type of green space surrounded by
walls on all four sides.

The selected courtyard is located enclosed in the centre of school buildings
with 12298cm2 area size. It is done during school holiday as it will be unoccupied
which help in controlling the gases uptake and discharge. The courtyard conditions
were differentiated with four types of plants volume (Figure 3.2). Details of the

34

courtyards are presented in table 3.1. Data collection for courtyard’s condition is done
in 24 hours duration with data reading every 30 minutes.

Table 3.1: Details of courtyard conditions

Courtyard Total plants Area covered
Plants Details
type volume with vegetation
No plants or 0
C1 0
grass
C2 Plants only 34306cm3 1573cm2

C3 Grass only 12298cm3 12298cm2

C4 Plants and Grass 631460cm3 12298cm2

Classroom

Classroom

Courtyard Laboratories
(Green Space)

Shelter

Corridor
Parking Area

Figure 3.1: Plan of the selected green space. The green space selected for this
study is a courtyard which surrounded by school buildings, and focused only
on the ground level

35

Figure 3.2: The courtyard conditions were differentiated with four types of plants volume

In the second category, data collection is done in a sealed glass box to control
other factor such as wind which might affect the data. The box is prepared using
transparent glass to enable sunlight penetration. This controlled environment
conditions were differentiated with three types of plants volume (Figure 3.3). Details
of the air-tight glass box are given in table 3.2. Data collection for controlled
environment conditions is done in 2 hours duration with data reading every 30
minutes.

Table 3.2: Details of air-tight glass box conditions

Box Total plants Area covered with
Plants Details
type volume vegetation
No plants or 0
B1 0
grass
B2 Plants only 23960cm3 2400cm2

B3 Grass only 2400cm3 2400cm2

36

Figure 3.3: The controlled environment conditions were differentiated with three types
of plants volume

3.3 Parameters

Parameters that involved in this study are Carbon Dioxide (CO2), Oxygen
(O2), Carbon Monoxide (CO), Temperature, and Relative Humidity. These were
chosen since it is related with the balanced condition of gases in atmosphere and
influences the outdoor thermal comfort.

3.4 Equipments

Four types of equipment used during data collection. The equipment used to
acquire the temperature data and relative humidity is Multi-detector LUTRON 4 in 1
LM-8000, a product of Taiwan. The concentration of carbon monoxide is detected by
Gray Wolf Direct Sense PPC Kit made from Germany. Carbon dioxide is detected
using TSI 7515 IAQ-CALC Carbon Dioxide Detector, and oxygen data is collected
by MSA Altair 4 Multi-Gas Detector (Figure 3.4). All the equipment is located in the
center spot during data collection for both the courtyard area and the air-tight glass
box.

37

Figure 3.4: The equipment used. From left TSI Carbon Detector, MSA Altair 4
Multi-Gas Detector, Multi-detector LUTRON 4 in 1, and Gray Wolf Direct Sense
PPC Kit

3.5 Methods Used to Calculate Plants Volume

There are several methods that can be used to calculate plants volume for
example Urban Forest Effects (UFORE) (David et al., 2005), and Street Tree
Resource Analysis Tool for Urban Forest Managers (STRATUM) (Wong et al.,
2006). In this study, the plants volume was calculated using the consideration of
estimated plants crown shape seen as a ratio to the cylinder (Gunther, 2008) (Figure
3.5). This method is similar to Bio-volume Calculation (Archana and Ankur, 2008),
and was chosen because it is more accurate and specific since the plants used in this
study is ornamental plants which usually used in the urban green space.

38

Figure 3.5: Methodology for calculating the green volume (Gunter, 2008)

3.6 Data Analysis

Subsequent to all the method done during desk study, field study and
observations, the data collected was analysed by plotting graph according to the
parameters involved and statistical analysis is carried to clarify and illustrate the result
gain from the method used.

CHAPTER 4

RESULTS AND ANALYSIS

4.1 Introduction

This chapter discussed on the results and analysis achieved from the data
collections. The discussion related with the literature review, method used and headed
for findings in conforming to the objectives of the study. The results of this study
focused on carbon dioxide, oxygen, temperature and relative humidity as well as final
discussion based on result from all conditions. Carbon monoxide is negligible in this
study as the data is not perceived at each and every condition in both categories.

4.2 Carbon Dioxide

Urbanization caused high accumulation of carbon dioxide (CO2) and leads to
the imbalance between atmospheric oxygen (O2) and CO2 (Mohammad, 1997). The
only natural mechanism known to utilize CO2 is photosynthesis. Figure 4.1 shows the
trend of CO2 changes for different courtyard conditions that are conditions C1 no
plants or grass, C2 plants only, C3 grass only, and C4 plants and grass. C1 has higher
CO2 level with average 502ppm almost 43% higher than normal CO2 concentration in
ambient air which is 350ppm. This is because according to Wisconsin Department of
Health Services (2008), CO2 concentration in normal outdoor air level is 250ppm
until 350ppm.

Peak photosynthesis

Figure 4.1: Comparison of carbon dioxide concentration according to different courtyard conditions
40

41

This is followed by C2 result with average concentration of CO2 of 431ppm
throughout the data collection. Meanwhile it was recorded below 350ppm during C3
and C4 with average 331ppm and 324ppm respectively. Thus this shows that CO2
reduction in C4 condition is higher than the other conditions. This is because the C4
condition has highest area coverage with vegetation and plant volume. However, one
of the interesting finding is even though the plant volume in C2 condition is higher
than C3, the average CO2 concentration of C3 condition is much lower with
differences of 23% compare with C2. This might be due to different area covered with
vegetation which is higher in C3.

Even though C3 has less plants volume than C4, from figure 4.1 shows that
the CO2 uptake for C3 trend is quite similar to C4. This illustrate that the area size
covered with vegetation is crucial in providing significant changes for CO2 trend.
However, there is still different in CO2 concentration (p < 0.05) as enclose in
Appendix B Table B1. Nevertheless C4 has the highest CO2 reduction with
differences of 3% compare to C3 condition since it has a higher plants volume with
all ground area covered with grass. This also can verify that the volume of plants is
important in assuring CO2 reduction. In addition, it agreed with the findings by
Fowler (2003) which indicate rates of transport of gases from the free atmosphere to
the surface are much greater over dense and high vegetation than over short
vegetation such as grassland.

The carbon-reduction phase of photosynthesis requires light. Consequently,
Figure 4.1 shows CO2 reduction happened particularly around 10:30am until 14:00pm
when most of the area received full solar intensity. This is because the site for data
collection is enclosed in between buildings which limit the solar path and intensity
(Figure 4.2). Thus affecting the light intensity and it form shadow cast throughout the
day (Figure 4.3 and Figure 4.4). However, C1 shows CO2 increment at that time
since no photosynthesis process occurs.

42

Figure 4.2: Solar intensity in courtyard area
changes throughout the day

Time 13:30
Time 10:30

Figure 4.3: Different solar intensity during morning and noon

Time 16:00 Time 04:00

Figure 4.4: Different solar intensity during evening and night

43

4.2.1 Day and Night Comparison

The carbon-reduction phase of photosynthesis requires light and will either
barely active or totally inactive in the dark (Vivekanandan and Sarabalai, 1997). This
is shown on figure 4.5 where the CO2 concentration uptake has decreased.

Figure 4.5 shows that the CO2 in C4 and C3 condition started to increase as
the sun falls. During night the photosynthesis process is barely active and plants usage
of CO2 has decreased. Plants utilize CO2 at night as there is no sunlight energy which
allows photosynthesis process to happen.

During day time from 8:00am till 19:00pm, the average CO2 concentration is
for C3 and C4 condition is 315ppm and 306ppm respectively. While during night time
starting from 19:00pm, the average CO2 concentration for C3 and C4 condition is
343ppm and 338ppm respectively. The difference is only 1% for the average CO2
concentration for C3 and C4 condition. C1 CO2 concentration reduces from the
highest peak that is 585ppm to 430ppm during 5:30am. This is 26% differences and
might be due to the absent of sunlight energy.

Significant differences of C3 and C4 condition throughout the day for CO2
concentration (p < 0.05) as enclose in Appendix B table B2. Thus shows that during
the night time the present of plants either with high or low volume is not obvious to
the CO2 changes. However this might be due to the plants conditions used in this
study which is low plantings.

Figure 4.5: Comparison of carbon dioxide concentration during day and night
44

45

4.2.2 Result from Controlled Environment

Table 4.1 shows B2 reduce 28% of the CO2 while B3 reduce 9%. Although
both B2 and B3 have same area covered with vegetation, the result shows that B2
with 10% more plants volume than B3 is the preferred condition. With the
differences of 19% in CO2 uptake, it can be concluded that by increasing the plants
volume more than 10%, the CO2 uptake will increase more than 15%. Thus these
result concluded that plants volume should be considered in implementing urban
green space as to give effect in CO2 reduction.

Table 4.1: Results shows carbon dioxide differences in various
conditions
No Plants Plants Grass
Time/Condition
(B1) (B2) (B3)
9:00 378 367 354
9:30 377 323 339
10:00 375 238 350
10:30 378 224 342
11:00 376 202 337
Average 377 271 344
Differences with B1
- -28% -9%
in percentage
(*Unit: ppm)

4.3 Oxygen

Oxygen (O2) makes up 20% to 21% of the Earth’s atmosphere (Williams,
2004; Ong et al. 2004; Godish, 2004). However Vesilind and Morgan (2004)
mentioned that such air composition is not found in nature and is of interest only as
reference. Therefore, on this study it is found that the oxygen reading is typically
20.8% and was set as the guideline in comparing any changes throughout the study.

Peak photosynthesis

Figure 4.6: Comparison of oxygen concentration according to different courtyard conditions
46

47

Plants were mentioned to release oxygen through photosynthesis (Wilhelim,
2008), and this process requires light which evidently shows on figure 4.6 which
illustrate the C4 and C3 data fluctuate. From Figure 4.6 shows C2 oxygen reading is
mostly constant except during noon. This most probably due to the small area covered
with vegetation which give less impact to the O2 trend.

The difference of C4 and C3 average is 0.29%. However, the C4 has 30%
higher O2 production compare with C3 throughout the day. Furthermore, the O2-
evolution activities for C3 end earlier than C. This might be due to the less volume of
plants in C3 thus less CO2 uptake needed for photosynthesis process. Substantial
different of all conditions (p < 0.05) has been pointed out as attached in Appendix B
Table B3.


As mentioned before, photosynthetic O2-evolution activity requires light.
Figure 4.7 signify the importance of light as energy in photosynthesis process because
from 17:00pm till 6:30pm no changes of O2 data. Compare with day time, the O2 data
during night time is not significant and as well as no sign of O2 reduction. This is
because although the amount of oxygen in the atmosphere is deteriorating, Jonathan
(2003) stated that there is plenty left for us to breathe and the total amount that has
been lost in the last 200 years is much less than one-thousandth of the oxygen in the
atmosphere.

Figure 4.7: Comparison of oxygen concentration during day and night
48

49


Oxygen result from controlled environment is negligible as the data has no
changes in every condition. This might due to loss of photosynthetic O2-evolution
activity since the plants acceptance temperature range is 15 ºC till 45 ºC (Dubey,
1997).

4.4 Carbon Dioxide and Oxygen

Data collection for carbon dioxide and oxygen are highlighted on C3 and C4
condition due to high differences. Substantial differences have been pointed out in
Appendix B Table B1 and Table B3. Figure 4.8 and figure 4.9 clearly show that when
the Oxygen (O2) data fluctuate, it is consistent with Carbon Dioxide (CO2) readings
that decreased during peak sunlight intensity. At time the O2 readings are back to
20.8%, the CO2 started to increase with time. It shows that CO2 level increase since
vegetation no longer utilizes CO2 for photosynthesis at night.

Figure 4.8: Comparison between carbon dioxide and oxygen concentration in courtyard
with grass and plants (C4)

50

The peak photosynthesis occurs from 10:30am to 14:00 pm where the area
received full sunlight. When comparing C4 and C3 during the peak photosynthesis,
the O2 data changes is more significant during C4 condition. The CO2 concentration
for C3 is slightly below 300ppm only for 1 hour while C4 has CO2 concentration
below 300ppm for 9 hours. Thus indicate that high plants volume help increase the
CO2 uptake.

For C4 condition, during this time O2 data recorded high in between 21.2% to
21.5%. From Figure 4.8, during C4 condition, the CO2 trend shows signs of midday
depression of photosynthesis. This can be determined by two-peaked diurnal course
(Xu and Shen, 1997). This phenomenon is common and related to intense light as well
as high air temperature because of enhanced CO2 efflux from respiration or
photorespiration. This shows that, even though the only natural mechanism known to
utilize atmospheric CO2 is photosynthesis by green plants, it still have the required of
certain conditions. As living things, plants may have their own setback which might
jeopardise the goal in reducing the CO2 atmospheric as well as its own life. Thus these
indicate that relying only on plants to control and manage the CO2 atmospheric
imbalance might not be the perfect solution.

Figure 4.9: Comparison between carbon dioxide and oxygen concentration in courtyard
with grass only (C3)

51

4.5 Carbon Dioxide and Temperature

The CO2 and temperature trend resulting from C1 agreed with the figures by
Jonathan (2003) and Al Gore (2006) which indicate that when there is more CO2 in
the atmosphere, the temperature increases (Figure 4.10). However, the trend change
when the vegetation is present and photosynthesis process occur. Even though the
temperature trend in C2 is similar with C1, it drops below average a few hours earlier
and the CO2 also decrease almost 14%. Substantial differences has been pointed out in
Appendix B table B1 and table B4.

From Figure 4.10, it shows that C2 condition has no significant changes of
CO2 data. This might be due to high temperature which affects plants growth,
metabolism and productivity. As mentioned before, elevated temperature leads to loss
of photosynthetic O2-evolution activity and limiting photosynthesis (Dubey, 1997).
Differences of both C2 and C1 condition in temperature value (p < 0.05) has been
pointed out in Appendix B Table B5. This shows that even small number of plant
volume is allocated, there is differences in temperature and CO2 concentration when
compare to deserted area.

From Figure 4.10 also indicate that the C4 temperature drops 2 hours earlier
when compare to C3. During 11:00am till 15:00pm, the temperature value for C3 is
higher when compare with C4. As discussed earlier, plants can offer cooling benefits
through two mechanisms that are direct shading and evapo-transpiration. In this case,
the plants selected are small plantings therefore indicate that by evapo-transpiration
alone can provide significant changes to the outdoor surroundings.

It is believed that C3 temperature drops rapidly compare to C4 because in C4
the plants upright and vertical volume trap heat which make the temperature change
gradually. Similarly to C2 when compare with C1 which indicate the temperature
decrease slowly and the data trend appear jagged.

(C1) (C2)

(C3) (C4)

Figure 4.10: Comparison between carbon dioxide concentration and temperature deviation in various conditions
52

(C1) no plants or grass, (C2) plants only, (C3) grass only, (C4) plants and grass

53

Based from Figure 4.10, Figure 4.11 is illustrated to shows that solar energy
reflected by earth surface and absorbed by vegetation in all four condition thus, giving
different result in both temperature and CO2 reductions. CO2 trend in C4 and C3
shows significant drop compare to C1 and C2. According to Kusterer (2007), the
percentage of solar energy that is reflected back to space is called the albedo.
Different surfaces have different albedos. Over the whole surface of the Earth, about
30 percent of incoming solar energy is reflected back to space. Rain forests and
vegetation surface reflect only a small portion of the Sun's energy. However, deserts
with no plants have high albedos (40%); they reflect a large portion of the Sun's
energy.

Figure 4.10 also illustrate that in C4 condition, CO2 decrease below 300 for 8
hours while C3 for 2 hours. Even though C4 and C3 has similar area size covered
with vegetation, this differences is due to higher plants volume which requires higher
CO2 uptake for photosynthesis process (Figure 4.10). Differences of both condition in
temperature value (p < 0.05) has been pointed out in Appendix B Table B2.

Figure 4.11: Solar energy reflected by earth surface and absorbed by vegetation in
various conditions (C1) no plants or grass, (C2) plants only, (C3) grass only, (C4)
plants and grass

54

4.6 Temperature and Relative Humidity

An average temperature in Malaysia is between 23.7ºC to 31.3ºC and the
average relative humidity throughout a day between 67% until 95% (Hussein and
Rahman, 2009). Thus shows that the maximum acceptance temperature is 31.3 ºC.
However, it is mentioned that temperatures above 30°C are usually considered
uncomfortable (Wang and Wong, 2007). Furthermore, changes in temperature often
lead to quite significant alterations to the relative humidity since air can hold more
water vapor at higher temperature, relative humidity values decrease as temperature
increases (Godish, 2004). This is clearly shows in Figure 4.12.

Furthermore, it is mentioned when temperature was 31°C and relative
humidity 69%, a wind speed of 5 ms- l or more is necessary to overcome heat
discomfort (Pakar, 1985). However, during this study, the wind speed is unnoticeable
when measured using Multi-detector LUTRON 4-in-1(Figure 3.4) which most likely
because the courtyard is surrounded by walls on all four sides. Thus, shows that the
relative humidity in this type of green space is preferred to be above 70% to provide
outdoor thermal comfort.

Figure 4.12 shows the significant differences of C1 and C4 for both relative
humidity and temperature. With differences of 47% increase for relative humidity and
12% decrease for temperature, staying in the C1 in the noontime is considered very
uncomfortable compared to C4. Temperature in C1 condition rose above 30°C
because there is no photosynthesis process which leads to CO2 accumulation. CO2
molecules known to absorb heat energy and in addition the heat builds up due to
building’s surface temperature and heat from earth surface.

C1 has average temperature of 33.3 °C and average relative humidity of 50%,
while C3 has average temperature of 29.7 °C and average relative humidity of 70.7%.
With difference of 29% for relative humidity and 10% for temperature, by introducing
only grass to the area, the thermal condition has been improved. Even though this type
of planting did not provide shade to the area, it still helps reducing the surrounding
temperature.

Full sunlight intensity

Figure 4.12: Comparison between temperature and relative humidity according to different courtyard conditions
55

56

C1 and C2 average temperature differences are only 2% even though there are
plants volumes in C2 condition. Differences of both conditions in temperature value
(p < 0.05) have been pointed out in Appendix B Table B5. These differences might be
due to less area covered with vegetation thus less incoming solar energy being
absorbed by plants. However, C1 and C2 average relative humidity differences is
23%. This is considered high difference which shows that being in the C2 condition is
preferable compare with C1 and even if with only 12% area covered with vegetation,
plants existence has modified the thermal comfort of C2 condition.

However, it is shown that even though C2 has more plants volume compare to
C3 condition, C3 result for both relative humidity and temperature is better. C2 has
average temperature of 32.4 °C and average relative humidity of 61.8%, while C3 has
average temperature of 29.7 °C and average relative humidity of 70.7%. These
indicate that being in the C3 condition is much more comfortable compare to in C2
condition. Even with low plant volume, increasing the area size covered with greenery
in C3 has increase 8% improvement of temperature and 12% of relative humidity.
This also shows that area size covered with vegetation is crucial in providing thermal
comfort in urban area.

C4 has average temperature of 29.1 °C and average relative humidity of
73.4%. When compared with C2, there are 15% differences in relative humidity and
10 % changes in temperature. Thus shows that by increasing the plant volume both
horizontally and vertically as shown in Figure 4.11 would help in increasing the
thermal comfort even if the plants did not offer shade. This might also indicate that by
providing plants with shade will help increase the thermal condition significantly
since it help reduce incoming solar energy and heat.

Even though C4 and C3 condition has small differences, with 4% differences,
it still gave impact to the ambient temperature particularly during afternoon from
13:30pm until 15:30pm. However differences of both condition in temperature value
(p < 0.05) has been pointed out in Appendix B table B6. Thus shows that by adding
more plants volume helps in improving the thermal conditions.

57


From Figure 4.13 show that being in all C1, C2, C3 and C4 conditions at night
is somehow tolerable. This is because almost in all condition the temperature is
mostly under 30°C. This might be due to the absent of sunlight. It is because one of
the important factors of atmospheric warming is the incoming solar energy which is
the ultimate energy source for all atmospheric processes (Bhatti et al., 2006).

Heat, according to Treshow and Anderson (1989), ultimately derived from
solar radiation and in this graph it shows that the temperature decrease as night falls.
However, the C1 condition is higher compare with the other conditions due to heat
released by the hard surface of the building and soils. Unlike the C1, the vegetation in
C2, C3 and C4 reflect only a small portion of the Sun's energy. Instead the vegetation
uses this energy to produced food. In C1 condition, the heat is reflected and absorbs
by the hard surface and it continued released heat at night. This has cause the heat
exchange near the surface which leads to high temperature and relative humidity.

Relative humidity trend at night time shows significant reduction for all four
conditions. C1condition shows increase of relative humidity around 21:00pm. Unlike
C3 and C4 which started to increase after 14:30pm when the area no longer received
full sunlight intensity (Figure 4.12). C2 shows changes and increase of relative
humidity trend starting from 17:00pm. This is when the area a fully shaded by the
building blocks from direct sunlight. However differences of all conditions in relative
humidity value (p < 0.05) has been pointed out in Appendix B Table B7. Thus shows
that by implementing vegetation to the area help increase the relative humidity and
this is important for the tropical climate because as Wong and Chen (2009)
mentioned, the reason for the high temperature and high relative humidity is it will
reduce the rate of evaporation of moisture from human body, especially in the
locations where the lack of air movement is experienced.

Figure 4.13: Comparison between temperature and relative humidity during day and night
58

59


Table 4.2 illustrate that the box with grass (B3) is warmer however, figure
4.14 shows that the solar energy absorbed by vegetation in B3 compare with B1 that
is empty thus absorbed less solar energy which turn into heat. The B3 has highest
temperature because CO2 molecules released by grass absorb heat energy, as well as
with the present of the grass which trapped in the box causes it to be warmer (refer
figure 4.14). Unlike plants in B2 which give off water vapor through the process of
transpiration which help in lowering the temperature. Even though grass in B3 did
undergo transpiration process due to the volume size the result is not perceive. B2
shows temperature decrease 2% compare with B1. From this shows that by increasing
12% plants volume help in reducing 2% temperature in average. Figure 4.14 shows
that the solar energy absorbed by vegetation compare with B1 that is empty thus
absorbed less solar energy.

Table 4.2: Results shows temperature differences in various conditions
No Plants Plants Grass
Time/Condition
(B1) (B2) (B3)
9:00 29.4 28.5 33.2

9:30 35.4 31.8 39.7
10:00 37.9 35.2 43.4

10:30 44.4 44.1 46.5
11:00 45.1 47.8 46.7

Average 38.4 37.5 41.9
Differences with B1
- -2% 9%
in percentage
(*Unit: Degree Celsius)

However, it is important to consider that firstly, the plant volume chosen for
this study did not give shade thus by implementing plants with shade would reduce
more temperature value. Secondly, even in the trapped condition where heat cannot be
released from the glass box, the plants activity has helped modified the temperature
thus shows that plants are important in improving the urban thermal environment.

Plants Volume as a Factor Affecting Outdoor Ambient Air and Thermal Condition

Plants Volume as a Factor Affecting Outdoor Ambient Air and Thermal Condition

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