“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 : ....................................................

iii

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

iv

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.

v

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.

vi

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.

vii

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

viii

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

ix

4.2.1 Day and Night Comparison 43

4.2.2 Result from Controlled Environment 45

4.3 Oxygen 45

4.3.1 Day and Night Comparison 47

4.3.2 Result from Controlled Environment 49

4.4 Carbon Dioxide and Oxygen 49

4.5 Carbon Dioxide and Temperature 51

4.6 Temperature and Relative Humidity 54

4.6.1 Day and Night Comparison 57

4.6.2 Result from Controlled Environment 59

5 CONCLUSION 62

5.1 Conclusion 62

5.2 Recommendation 63

LIST OF REFERENCES 65

APPENDIX 71

x

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

xi

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

xii

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

xiii

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

xiv

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,

2

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.

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).

Table 2.1: Gaseous mixture surrounding the Earth

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.

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

Figure 2.1: Atmospheric CO2 is essential to most plants and animal life

on earth (Williams, 2004)

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.

9

RH = (2.5)

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%

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.

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

Absorbed Atmosphere

Surface

Subsurface

Reflected Absorbed

Atmospheric

Processes Radiation from

the Earth

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.

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.

Figure 2.3: The incoming solar energy that causes the warming or earth surface in

percentage (Kusterer, 2007).

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).

15

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

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).

Figure 2.6: A densely planted area is highly preferred and provides greater visual

interest than a sparsely planted one

19

Urban Green

Artificial formation Natural formation

Natural reserve

Landscape on the ground

City Park

Courtyard

Other green areas

Rooftop garden

Balcony garden

Vertical landscaping

Landscape on buildings

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

Figure 2.8: Green roof in Fukuoka, Japan

20

Figure 2.10: Vertical garden in Huntsville Alabama

Figure 2.9: Terrace garden in Prague Castle Garden, Prague

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.

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

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

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).

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.

Figure 2.12: Temperature decrease as plants help cool urban climates through shading and

evapo-transpiration (Wilhelim, 2008)

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.

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.

Figure 2.13: Evapo-transpiration process influence

the outdoor temperature and relative humidity

(Williams, 2004)

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.

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).

Figure 2.14: Photosynthesis is the conversion of solar energy

into chemical energy, which is stored in sugar (Williams, 2004)

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.

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

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)

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

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.

Figure 2.16: Transfer processes for gaseous and particulate pollutants from the

free atmosphere to terrestrial surfaces (Fowler, 2003)

Grass / Vegetation

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.

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

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

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

type Plants Details

Total plants

volume

Area covered

with vegetation

C1 No plants or

grass 0

0

C2 Plants only 34306cm3 1573cm

2

C3 Grass only 12298cm3 12298cm

2

C4 Plants and Grass 631460cm3 12298cm

2

Classroom

Lab

orato

ries

Parking Area

Classroom

Corridor

Shelter

Courtyard

(Green Space)

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

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

type Plants Details

Total plants

volume

Area covered with

vegetation

B1 No plants or

grass 0

0

B2 Plants only 23960cm3 2400cm

2

B3 Grass only 2400cm3 2400cm

2

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

36

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.

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

of plants volume

37

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.

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

38

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.

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

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.

40

Figure 4.1: Comparison of ca

rbon dioxide co

ncen

tration acc

ording to different courtyard conditions

Peak photosynthesis

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 4.3: Different solar intensity during morning and noon

Time 10:30 Time 13:30

Figure 4.4: Different solar intensity during evening and night

Time 16:00 Time 04:00

Figure 4.2: Solar intensity in courtyard area

changes throughout the day

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.

44

Figure 4.5: Comparison of ca

rbon dioxide co

ncen

tration during day

and night

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

Time/Condition No Plants

(B1)

Plants

(B2)

Grass

(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

in percentage - -28% -9%

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.

(*Unit: ppm)

46

Figure 4.6: Comparison of oxygen

conce

ntration acc

ording to different co

urtyard conditions

Peak photosynthesis

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.

4.3.1 Day and Night Comparison

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.

48

Figure 4.7: Comparison of oxygen

conce

ntration during day and night

49

4.3.2 Result from Controlled Environment

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.

52

Figure 4.10: Comparison betwee

n carbon dioxide co

ncen

tration and tem

perature dev

iation in various conditions

(C1) no plants or grass, (C

2) plants only, (C

3) grass only, (C

4) plants and grass

(C1)

(C2)

(C3)

(C4)

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.

55

Figure 4.12: Comparison betw

een temperature and relative humidity acc

ording to different courtyard conditions

Full sunlight intensity

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

4.6.1 Day and Night Comparison

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.

58

Figure 4.13: Comparison betwee

n tem

perature and relative humidity during day

and night

59

4.6.2 Result from Controlled Environment

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

Time/Condition No Plants

(B1)

Plants

(B2)

Grass

(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

in percentage - -2% 9%

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.

(*Unit: Degree Celsius)

60

Table 4.3 shows B2 has high relative humidity percentage due to the high

volume size of plants and also high transpiration or evaporative cooling of the plants

which make water vapor traps inside the box (refer figure 4.15). After some times,

there are vapor covering the glass and liquid on the glass surface which make the

condition inside the box appear suffocating. This shows the side effect of high relative

humidity which will offset thermal comfort especially when the temperature is high

and no wind to overcome heat discomfort. Furthermore, both the B2 and B3 shows

increase value of relative humidity.

Table 4.3: Results shows relative humidity differences in various

conditions

Time/Condition No Plants

(B1)

Plants

(B2)

Grass

(B3)

9:00 65 84.4 66.9

9:30 58.7 82.3 64.8

10:00 56.5 81.1 63.6

10:30 55.7 81.8 63.5

11:00 38.4 64.8 51.3

Average 54.9 78.9 62.0

Differences with B1

in percentage - 44% 13%

(*Unit: RH %)

Figure 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

61

From the observation, even though the grass did increase 13% of relative

humidity however the grass in B3 died the next hour due to intense sunlight and high

temperature (refer Table 4.2). From the temperature and relative humidity

observation, it illustrate that by increasing 10% of the plants volume, the thermal

environment would be better because even if the temperature increase more than 20%,

the thermal comfort can still be achieved. Thus this shows that in urban area which

usually has high temperature requires green space with high plant volume. This is

because, even though the plants did not give shade, when it has more volume, it can

help modify the outdoor thermal comfort and give balance between temperature and

relative humidity.

Figure 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

CHAPTER 5

CONCLUSION

5.1 Conclusion

Increasing plants volume has shown potential in improving air quality and

outdoor thermal conditions. The changes of carbon dioxide, oxygen, temperature and

relative humidity are found to be significant according to various plants volume

allocation. However, the size of horizontal area is much more crucial and when

compliment with vertical plants volume indicate significant CO2 reduction and

photosynthetic O2-evolution. From this study, result shows that by increasing the

plants volume more than 10%, the CO2 uptake will increase more than 15%.

Furthermore, rates of transport of gases from the free atmosphere to the surface are

much greater over vegetation with vertical volume than over short vegetation such as

grassland. With this it shows that green space size in urban area should be reserved

more and the plants within it should have more volume. Consequently this could help

improving the urban surrounding and thermal condition.

Plants certainly help promote outdoor thermal comfort because even though

the temperature in the urban area is high, plants selection with more volume and

height help cools down the surrounding by transpiration. This can be perceived even

more if both the plants volume and surface area covered with vegetation is increased.

It is because from this study it was found that by increasing 10% of the plants volume,

the thermal environment would be better because even if the temperature increases

more than 20%, the thermal comfort can still be achieved. Plant can give balance

63

between temperature and relative humidity thus helps modify the outdoor thermal

comfort. Therefore this shows that capability of high plants volume in improving

outdoor ambient air and thermal improvement has been identify.

Furthermore, plants and trees having thick canopies and dense foliage provide

the most benefits. Therefore, when proposing and implementing urban green space

especially in tropical country, it is important to consider plant in volume size.

However, it is important to note that the artificial formation should never be viewed

as a satisfactory alternative to losing nature. Natural environment and native plants

are best to be preserved at all costs.

Even though the only natural mechanism known to utilize CO2 is

photosynthesis, it is important to consider that relying on green space and plants

volume alone will not formulate a better environmental quality. Nevertheless it is

partly as a function that contributing towards enhanced outdoor environment and

maintenance of ecological system in urban area.

5.2 Recommendation

There are several suggestions that recommended to be implemented when

designing for the outdoor urban green space as to improve the ambient air and thermal

condition:

(i) Plants and vegetation should be introduced extensively yet carefully in

urban areas. Selection of plants and vegetation in urban green space

should consider the size of horizontal area covered with vegetation, as

well as vertical plants volume.

(ii) Plants and vegetation implemented in between buildings blocks or

urban high rise should be located accordingly as to receive full sunlight

in the highest amount of time possible.

64

(iii) Plant should be strategically introduced into buildings, horizontally

and vertically as well as with height and volume as to optimize the

capability of green plants as the only natural mechanism known to

utilize atmospheric CO2.

(iv) Spaces in between building without good ventilation could trap heat

thus need profound consideration on design and arrangement of

openings that allows air movement.

(v) High relative humidity will offset thermal comfort especially when the

temperature is high and no wind to overcome heat discomfort.

Therefore it is important to consider the advantage and disadvantage of

locating plants in the enclosed area as it will affect the temperature as

well as the humidity.

65

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