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

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

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  • 1. “I hereby declare that I have read this thesis and in my opinion this thesisis 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 : ....................................................
  • 2. PLANTS VOLUME AS A FACTOR AFFECTINGOUTDOOR AMBIENT AIR AND THERMAL CONDITION SITI RAHMAH OMAR A project report submitted in partial fulfillment of the requirements for the award of the degree ofMaster of Engineering (Civil – Environmental Management) Faculty of Civil Engineering Universiti Teknologi Malaysia APRIL 2010
  • 3. 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 researchexcept 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 : ....................................................
  • 4. iiiTo 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
  • 5. iv ACKNOWLEDGEMENT In the name of God, the most gracious, the most compassionate, I am gratefulthat in preparing this thesis, I was in contact with many people, researchers,academicians, and practitioners. They have contributed towards my understandingand thoughts. In particular, I wish to express my sincere appreciation to mysupervisor, Assoc. Prof. Dr. Johan Sohaili, for encouragement, guidance, and critics.Without the continued support and interest, this thesis would not have been the sameas presented here. I am also indebted to the environmental laboratories technicians fortheir 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 haveprovided assistance at various occasions. Their views and tips are useful indeed. Lastbut not least, I am also grateful to all my family members for their patient and love.
  • 6. v ABSTRACT This study evaluates the effectiveness of plants for outdoor ambient air andoutdoor thermal improvement based on volume size. The growing conceptualizationof green space is partly as a function that contributing towards a better environmentalquality and maintenance of ecological system in urban area in giving evidence tosustainable urban living. However, the general requirement for plantings in designatedurban green spaces is 4% from the whole development without reckoning the heightor volume of the plants which should be considered in providing outdoor thermalcomfort and clean air. Focusing on ambient air quality, this study quantify amount ofcarbon dioxide, oxygen, temperature and relative humidity influence by plants volumebased on field data. Result shows that there is influence of plants volume in greenspace to the pattern of air chemical composition in an outdoor space. The study alsoconcluded that the design and planning of green space should give more considerationon both the plants volume and area size especially in a tropical country like Malaysia,in order to enhance air quality and thermal comfort.
  • 7. vi ABSTRAK Kajian ini dilakukan bertujuan mengkaji keberkesanan tumbuhan berdasarkankepadatan pokok terhadap keadaan udara dan suhu di persekitaraan luar. Konsepruang hijau yang semakin menjadi perhatian ramai adalah salah satu faktor yangmenyumbang kepada keadaan persekitaran yang lebih baik dan juga terhadapkelestarian ekologi di kawasan bandar yang kini semakin pesat membangun. Walaubagaimanapun, telah dinyatakan bahawa keperluan asas untuk tumbuhan dan tanamandalam ruang hijau yang disediakan di kawasan bandar adalah 4% dari keseluruhanpembangunan itu. Ini tidak mengambil kira ketinggian atau kepadatan tanamandimana ia didapati perlu diambil kira untuk memberi kesan terhadap kualiti udara dankeselesaan suhu di persekitaraan luar. Oleh yang demikian, kajian ini mengenal pastijumlah perubahan kandungan karbon dioksida, oksigen, suhu dan kelembapan udarayang dipengaruhi oleh tumbuhan berdasarkan kepadatan pokok dari kajian lapangan.Daripada kajian yang dibuat, dapat di rumuskan bahawa jumlah kepadatan pokokmempengaruhi komposisi udara di kawasan persekitaran luar. Ini menunjukkanbahawa perancangan dan rekabentuk ruang hijau di kawasan bandar seharusnyamengambil kira kedua-dua faktor iaitu kepadatan tumbuhan dan juga keluasankawasan hijau yg di cadangkan terutama sekali di kawasan beriklim tropika sepertiMalaysia. Ini penting bagi membantu meningkatkan kualiti udara dan suhu yangmenyumbang kepada keadaan persekitaran yang lebih baik dan juga terhadapkelestarian kawasan bandar.
  • 8. vii TABLE OF CONTENTSCHAPTER 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
  • 9. viii2 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 293 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 384 RESULT AND ANALYSIS 39 4.1 Introduction 39 4.2 Carbon Dioxide 39
  • 10. 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 595 CONCLUSION 62 5.1 Conclusion 62 5.2 Recommendation 63 LIST OF REFERENCES 65 APPENDIX 71
  • 11. x LIST OF TABLESTABLE NO. TITLE PAGE2.1 Gaseous mixture surrounding the Earth 63.1 Details of courtyard conditions 343.2 Details of air-tight glass box conditions 354.1 Results shows carbon dioxide differences in various conditions 454.2 Results shows temperature differences in various conditions 594.3 Results shows relative humidity differences in various conditions 60
  • 12. xi LIST OF FIGURESFIGURE NO. TITLE PAGE2.1 Atmospheric CO2 is essential to most plants and animal life on earth 72.2 Representation of the greenhouse effect 112.3 The incoming solar energy that causes the warming or earth surface in percentage 132.4 The absorptivity of various gases as a function of wavelength 142.5 New York Central Park. Shows green space is everywhere even in the biggest city 162.6 A densely planted area is highly preferred and provides greater visual interest than a sparsely planted one 182.7 Formation of urban green and greening considerations 192.8 Green roof in Fukuoka, Japan 192.9 Terrace garden in Prague Castle Garden, Prague 202.10 Vertical garden in Huntsville Alabama 202.11 Courtyard is surrounded by walls on all four sides 212.12 Temperature decrease as plants help cool urban climates through shading and evapo-transpiration 222.13 Evapo-transpiration process influence the outdoor temperature and relative humidity 232.14 Photosynthesis is the conversion of solar energy into chemical energy, which is stored in sugar 25
  • 13. xii2.15 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 262.16 Transfer processes for gaseous and particulate pollutants from the free atmosphere to terrestrial surfaces 292.17 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. 313.1 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 343.2 The courtyard conditions were differentiated with four types of plants volume 353.3 The controlled environment conditions were differentiated with three types of plants volume 363.4 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 373.5 Methodology for calculating the green volume 384.1 Comparison of carbon dioxide concentration according to different courtyard conditions 404.2 Solar intensity in courtyard area changes throughout the day 424.3 Different solar intensity during morning and noon 424.4 Different solar intensity during evening and night 424.5 Comparison of carbon dioxide concentration during day and night 444.6 Comparison of oxygen concentration according to different courtyard conditions 464.7 Comparison of oxygen concentration during day and night 484.8 Comparison between carbon dioxide and oxygen concentration in courtyard with grass and plants (C4) 494.9 Comparison between carbon dioxide and oxygen concentration in courtyard with grass only (C3) 50
  • 14. xiii4.10 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 524.11 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 534.12 Comparison between temperature and relative humidity according to different courtyard conditions 554.13 Comparison between temperature and relative humidity during day and night 584.14 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 604.15 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
  • 15. xiv LIST OF ABBREVIATIONS°C - Degree CelsiusCO2 - Carbon DioxideH2O - WaterO2 - Oxygenppm - Parts per millionRH - Relative HumidityVOCs - Volatile organic compounds
  • 16. CHAPTER 1 INTRODUCTION1.1 Introduction The world has experienced unprecedented urban growth in the last and currentcenturies. Wong and Chen (2009) mentioned that in 1800, only 3 per cent of theworld’s population lived in urban areas and this began to increase significantly after1900. This rapid urbanization has resulted in environmental changes. According toKiran 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 anecological balance and without them, not only many of the earth’s inhabitants die, butalso the earth itself would suffer. Changes in urban conditions are also mentioned to have often causeddeterioration in environmental quality and may result in damage to the health of city-dwellers (Wilhelm, 2008). One of the alarming concerns is the degradation ofambient air quality. The urban building and economic activity result in pollution andwarming 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 parksand green space as well as using plants on both vertical and horizontal surfaces sinceplants have proved their resistance to urban environmental stress. Consequently, this shows that urban area and cities needs green spaces such aspark and garden. Herbert (2002) mentioned that if cities were compared to organisms,
  • 17. 2parks and garden situated within it acts as the ‘green lungs’. This is because creationof green spaces, especially with trees and vegetation could promote in human andurban ecology well being. Therefore, proposed green spaces were considered asessential ‘breathing spaces’ within the built environment (Peter, 2006), because of theplants activities which enhanced the balanced conditions of the atmosphere. Currently, green spaces in Malaysian urban area are usually proposed andreserved 10% from the whole development area (Jabatan Landskap Negara, 2008).This artificial formation of green spaces is usually planned and landscaped in theprocess of urbanization. Wong and Chen (2009) stressed that, the artificial formationof green space is the windows and links from which the urban dwellers can accessMother Nature in the harsh built environment. Passive interaction with nature andplants in urban green space has also been associated with many beneficial responses,including reductions in stress, improvements in health, and restoration from mentalfatigue. Thus shows plants play a major role in providing better urban environment aswell as human and urban ecology well being.1.2 Problem Statement The benefits of greening the urban area have been taken for grantedwhen 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 needscientific input; how many plants should be introduced and how much theenvironment will respond. The proposed plants in urban green space are also usually small andhave less volume compared to the existing mature plants which usually being torndown during the site clearance for new development. Even though new plantings willbe planted again, the significant size different did affect the urban outdoorsurroundings and urban ecology well being. Furthermore, the formations of green areawhich are proposed and designed did not truly consider the amount of plantings andits dense value in improving the outdoor environment. Thus shows that, the outdoor
  • 18. 3plantings and urban green space need to be consider quantitatively and supported theenvironmental balanced and physical needs in regards with ambient air and thermalcondition.1.3 Aim and Objectives The aim of the study is to determine the effect of plants in volume size onoutdoor ambient air and thermal conditions. The objectives of this study are as thefollowings: (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. Itis rare to have natural formation of aboriginal plants in an urban environment due tothe constraint of space. This study will select the artificial formation of green areawhich also known as green space. Parks, garden, courtyard, green roofs, green wallsor terraces are all artificial formations which are planned and landscaped in theprocess of urbanization. Thus, this study will focus only on courtyard which is one ofthe artificial formations of green space in urban area. The plants selection for thisstudy will be ornamental plants or low shrubs. This is because large plants or treesgives shade and this could not justify the plants volume capability in improvingoutdoor ambient air and thermal improvement.
  • 19. 4 However, the study will not deal with the species and arrangement of plantingas 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 idealenvironment 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 beintroduced and how much the environment will respond (Wong and Chen, 2009). InMalaysia, Jabatan Landskap Negara (2008) stated that the green space in urban areashould consist minimum 40% of soft landscape. However this 40% is basically totalcovered area of greenery without reckoning the size, height or volume of the plants. The proposed plantings and vegetation in urban area should be consideredquantitatively as to provide and support the urban environment balanced and physicalneeds. In this context it can be argued that the role of green space as an environmentalaid in urban area necessitates an evaluation of plants quantity required in the greenspace in regards to air quality and thermal conditions. The evaluation will provideunderstanding on plants in volume size effect to the outdoor ambient and willhopefully benefits towards a better outdoor urban green space.
  • 20. CHAPTER 2 LITERATURE REVIEW2.1 Introduction This chapter discussed on natural ambient air, urban context andenvironmental changes as well as urban green space and plants within it. It is focusedon the outlined as well as related topics and was based on the needs to understand theattributes and insight into the possible outcome throughout the study. This is also forfurther understanding in the study topics, provides information to support the study’sresult 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 naturalatmosphere is seldom thought of as harmful or damaging, nevertheless, within theatmosphere exist great treats to all life. In its present state, the consequences ofchanges could be more severe, therefore it is important to understand the naturalatmosphere 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 onlysurvive for about three to four minutes without air. For this reason, it is the single
  • 21. 6most important resource we have. Williams (2004) stated that all the otherenvironmental concerns attach into the preservation of our atmosphere. Natural ambient air is a gaseous mixture surrounding the Earth atmospherewhich 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 particlesand microorganisms. Shown on Table 2.1, Oxygen has 21% of the gaseous mixturesurrounding the Earth. Based on several references, it indicates that Oxygen makes up20% 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 asreference.2.2.1 Carbon Dioxide Atmospheric carbon dioxide (CO2) is essential to most present day plant andanimal life on earth because it provides the carbon input to photosynthesis (Figure2.1). However, the significant release of CO2 into the atmosphere caused airdegradation and imbalance resulting from activities such as the combustion of fossilfuels and changes in land use especially deforestation that constitute the primarydetectable human influence on global climate (Runeckles, 2003).
  • 22. 7 Some of the carbon dioxide removed from the atmosphere by photosynthesisand some will absorb by the ocean enough to restore equilibrium or atmosphericbalance (Treshow and Anderson, 1989). Now that CO2 is building up in theatmosphere, further actions should be taken. Adding to our concern is that the forestsare being destroyed and this is a highly concerned matter since the trees and plants actas 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 themean global temperature by 1.1°C to 4.5°C. Jonathan (2003), Runeckles (2003), andAl Gore (2006) discussed that there is interrelationship between temperature and
  • 23. 8atmospheric CO2 concentration within earth’s complex land-ocean-atmospheresystem. It indicates that when there is more CO2 in the atmosphere, the temperatureincreases. Thus shows that CO2 is thought to be dominating the heating up of theworld 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 thedegradation of organic material. As one would expect the oxygen concentration in theatmosphere is slowly declining if plants and fossil fuel carbon is being burned to giveCO2. 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 beenlost in the last 200 years is much less than one-thousandth of the oxygen in theatmosphere. Fishman (1990) stated that ozone (O3) forms readily in the stratosphere asincoming ultraviolet radiation breaks molecular oxygen (two atoms) into atomicoxygen (a single atom). In that process, oxygen absorbs much of the ultravioletradiation and prevents it from reaching the Earth’s surface where we live. He alsomentioned four simplified chemical formula as the explained below. O2 + sunlight O + O (2.1) When an electrically excited free oxygen atom encounters an oxygenmolecule, they may bond to form ozone. O + O2 O3 (2.2) Destruction of ozone in the stratosphere takes place as quickly as formation ofozone, because the chemical is so reactive. Sunlight can readily split ozone into anoxygen molecule and an individual oxygen atom.
  • 24. 9 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 rapidlyand constantly, maintaining an ozone layer. The evolution of free atmospheric oxygen at elevated concentrations set thestage for the evolution of oxidative metabolism, the series of energy-transferringchemical reactions that sustain most life forms. Oxygen, as consequence, is vital toalmost all living things.2.2.3 Temperature and Relative Humidity Relative humidity is the relationship between the air temperature and theamount of water vapour it contains. On the other hand, humidity is the amount ofwater vapour in the air. When it has been raining and the air is saturated, there is 99 to100 percent humidity. Relative humidity is expressed in percent and this can bewritten as an equation (2.5). Godish (2004) explained that it is the percent of air (H2Ovapour a volume) holds at a given temperature. Since air can hold more H2O vapourat 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-
  • 25. 10year period records the outdoor temperatures are relatively uniform. The averagetemperatures between 23.7ºC to 31.3ºC throughout a day with the highest maximumrecorded as 36.9ºC and the average relative humidity throughout a day is between67% to 95%. The reason for the high temperature and high relative humidity is it willreduce the rate of evaporation of moisture from human body, especially in thelocations where the lack of air movement is experienced (Wong and Chen, 2009). According to Laurie (1979), when it is desirable to increase humidity, treescan be a valuable mechanism for moderating urban microclimate. This is because aswater is released through plants’ stomata, it evaporates into atmosphere. Asevaporation takes place atmospheric moisture content or humidity is increased. Thusthis is important because Laurie (1979) also stated that the control of urbanmicroclimates and temperature is related to the control of humidity as well as solarradiation and wind.2.2.4 Wind Wind is important as a natural cooling strategy in the tropics. Wind asmentioned by Williams (2004) is a product of atmospheric air pressure that is causedby 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 asmentioned by Godish (2004) is the term commonly used to describe air movement inthe horizontal dimension. As mentioned by Yabuki (2004), wind is considered asenvironmental factors for plants growth and it effect the gasses exchange between airand plants. For outdoor environment, the effect of wind is more complicated as it is ofteninter-related with solar exposure. A review of outdoor thermal comfort studies (Chengand Ng, 2008) has showed that at air temperature of about 28°C, the comfort windspeed for a pedestrian in shade could vary from 0 to 3 m/s. Therefore a high wind
  • 26. 11speed is needed to compensate for the high temperature in order to achieve thermalcomfort. Wind not only moves the pollutants horizontally, but it causes the pollutants todisperse (Speight and Lee, 2000), reducing the concentration of the pollutant withdistance away from the source. According to Vesilind and Morgan (2004), the amountof dispersion is directly related to the stability of the air, or how much vertical airmovement is taking place. Thus shows that in wind is considered as one of theimportant factor in the atmosphere.2.3 Atmospheric Imbalanced and Warming According to Davis and Masten (2004), the atmosphere is somewhat likeengine. It is continually expanding and compressing gases, exchanging heat, andgenerally creating chaos. The change in the element of the atmosphere is the tendencyfor the temperature close to the earth’s surface to rise. This is a phenomenon referredas the greenhouse effect (Speight and Lee, 2000). This term is used to describe thewarming or rise in the temperature of the earth when the energy from the sun istrapped 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)
  • 27. 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 alsomentioned that air becomes polluted when it is changed by the introduction of gasesor particulate substances or energy forms so that the locally, regionally, or globallyaltered atmosphere poses harm to humans, biological systems, materials, or theatmosphere itself. Levels of pollution experienced by cities and buildings can be greatlyinfluenced by location, morphology and the local climate (Susan et al., 2004).Moreover, indoor air pollution is stated linked with the outdoor air pollution orambient air pollution that occurs in both urban and rural areas. One of the important factors of atmospheric warming is the Sun which is theultimate energy source for all atmospheric processes (Bhatti et al., 2006). Solarradiation is also the main energy input factor that determines plants growth andproduction. Heat, ultimately derived from solar radiation, can be transferred to theatmosphere in four different ways (Treshow and Anderson, 1989). First is byconduction, secondly is by convection where air is warmer near the ground, causing itto expend and rise. A third way by which heat transferred to the atmosphere is bymeans of evaporation. Finally is the thermal radiation. Visible light is partly thermal radiation. The atmosphere reflects scatters andabsorbs some of the solar radiation that passes through it. Thus shows that theatmosphere already exhibits a greenhouse effect by absorbing some of the outgoingthermal radiation and warning the earth. Furthermore, warming of the earth also dueto soil temperatures under sealed surfaces are clearly higher than the average and inthe 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 fromsurface radiation, and the final 15% as surface radiation which is absorbed by theatmosphere & clouds before being radiated out to space. 29.4% of the energy radiated
  • 28. 13from the Earths surface is absorbed by the atmosphere.70.6% of the energy heats theatmosphere by other means. Of the 29.4%, a tiny portion will be in the absorptionband 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 isreflected 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 iscalled the albedo. Different surfaces have different albedos. Over the whole surface ofthe Earth, about 30 percent of incoming solar energy is reflected back to space. Oceansurfaces (26% albedo) and rain forests (15% albedo) reflect only a small portion ofthe Suns energy. Deserts however, have high albedos (40%); they reflect a largeportion of the Suns energy. Thus shows that forest absorbs the solar energy whichhelps reduce heat and temperature. Even if the greenhouse gases traps the heat fromearth, by increasing vegetation area the energy from sun will be used accordingly.
  • 29. 14 Unfortunately, the problem faced by the world today is the additional warmingthat is being produced by several natural anthropogenic gases that being injected intothe global atmosphere by human activities and urbanization. Treshow and Anderson(1989), stresses that we are not only facing a greenhouse effect, but super-greenhouseeffect due to both natural and additional warming. It is also important to understand that various gases that made up Earthatmosphere absorbs heat energy at specific wavelengths. Figure 2.4 shows theabsorptivity of various gases as a function of wavelength (Vesilind and Morgan,2004). Carbon dioxide absorbs almost none of the sunlight coming to Earth becauseits 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 2.4however, it is clear that carbon dioxide can be effective energy absorber at thefrequencies normal to heat radiation from earth. Figure 2.4: The absorptivity of various gases as a function of wavelength (Vesilind and Morgan, 2004).
  • 30. 152.4 Urban Context and Environmental Changes The world has experience unprecedented urban growth. In the last andcurrent centuries has lead to rapid urbanization and for the past two centuries resultedin significant environmental changes (Wong and Chen, 2009). Changes in urbanconditions are also mentioned to have caused deterioration in environmental qualityand cause damage to the health of urban-dwellers (Wilhelm, 2008). One of thealarming concerns is the degradation of air quality. The urban building and economicactivity also result in pollution and warming of the air. Furthermore, the change ofurban climate, especially micro-climate, is definitely associated with the rapidurbanization. Higher temperature in urban areas means hazards of thermal discomfort,air pollution and even water pollution. Furthermore, natural elements including thefresh 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 thereplacement of the natural surface of soil, grass, and plants by the multiplicity ofurban surfaces of brick, concrete, glass, and metal at different ground. According toBerry (1990), these artificial materials change the nature of the reflecting andradiating surfaces, the heat exchange near the surface, and the aerodynamic roughnessof the surface. Since hard surfaces predominate in urban areas, during periods ofintense incoming radiation, the temperature are likely to be higher in urban area thanin the suburbs or countryside. Laurie (1979) stated that particularly in the central areasof large urban development, this can be result in temperatures being raised by 4°C to6°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 fabricscompared with natural soils. This promotes the twin processes of heat storage duringthe day and subsequent release of the stored heat at night. Furthermore, the input ofenergy from artificial sources and the contribution made by solar radiation, lead to thehigh proportion of pollutants in the atmosphere above towns compared to the opencountryside.
  • 31. 16 Moreover, the pollution level in the urban atmosphere still frequently remainsabove the limits normally considered to be safe for human (Laurie, 1979). Thus, interm of preventive or protective environmental actions, Wilhelm (2008) mentionedthat one of the methods is to increase size of urban parks and green space as well asusing plants on both vertical and horizontal surfaces. Wong and Chen (2009) alsosuggested 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 andsuburban area (Peter, 2006). Green space of course is not always perfectly green, andit is everywhere even in the biggest city (Figure 2.5). The purpose of proposing urbangreen 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 itscomplexity is partly a function of lobbying for better environmental quality andmaintenance of ecological systems in urban area. Figure 2.5: New York Central Park. Shows green space is everywhere even in the biggest city
  • 32. 17 Consequently, this shows that urban area and cities needs green spaces such aspark and garden. According to Laurie (1979), urban green space could be consideredas a place that functions as an enrichment of the environment, for intimacy ofcharacter and for modification of the climate. Herbert (2002) mentioned that if citieswere compared to organisms; parks and garden situated within it acts as the ‘greenlungs’. This is because creation of green spaces, especially with trees could promotein human and urban ecology well being. Therefore, proposed green spaces wereconsidered as essential ‘breathing spaces’ within the built environment (Peter, 2006). The green spaces in urban area are planned and landscaped. This artificialformation is simply the compromise to rapid urbanization. As a precious resource, itis the windows and links, from which the urban dwellers can access Mother Nature inthe harsh built environment (Wong and Chen, 2009). Ulrich (1981) found that scenesof natural environments have more positive influence on human emotional states. Moreover, the outdoor environment or green space as mentioned by Said etal., (2004) is known to have restorative power. It is because man recognises thephysical and symbolic benefits of plants, fresh air, sunlight and scenic views for morethan one thousand years ago. Currently, green spaces in Malaysian urban area areusually proposed and reserved 10% from the whole development area, and from this10%, it should consist minimum 40% of soft landscape or plantings (JabatanLandskap Negara, 2008). Even if it lack of detailed indicator of plants quantity andquality that should be chosen and proposed, this guideline helps in promoting moregreenery in the buildup area. People and urban dweller enjoy contact with nature; however it is not enoughsimply to plant a few trees and set down a bench or two. For instance, according toCarpman and Grant (1993) a densely planted area such as shown in Figure 2.6 ishighly preferred and provides greater visual interest than a sparsely planted one. Theyalso pointed out that there are findings shows that scenes with greater number of treeswere consistently rated higher than those with fewer trees. Thus shows that plantsplay a major role in the urban green space.
  • 33. 18 Figure 2.6: A densely planted area is highly preferred and provides greater visual interest than a sparsely planted one2.5.1 Types of Urban Green Space Owing to its importance, vegetation always accompanies the growth of citiesin 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 majorcategories are natural and artificial. It is rare to have natural formation of aboriginalplants in an urban environment due to the constraint of space. Parks, garden,courtyard, green roofs, green walls or terraces are all artificial formations which areplanned and landscaped in the process of urbanization. Figure 2.7 also shows thatartificial formation can be further divided into two groups. One is landscaping on theground which fills in the public areas in urban environment for example parks,courtyard and garden. The other group under artificial formations is landscaping onbuildings. This includes rooftop gardens or green roof (Figure 2.8), terrace gardens(Figure 2.9) and vertical landscaping (Figure 2.10).
  • 34. 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 landscapingFigure 2.7: Formation of urban green and greening considerations (Wong and Chen, 2009) Figure 2.8: Green roof in Fukuoka, Japan
  • 35. 20Figure 2.9: Terrace garden in Prague Castle Garden, Prague Figure 2.10: Vertical garden in Huntsville Alabama
  • 36. 21 Courtyard as shown in figure 2.11 which is the focus of this study is a type ofgreen space surrounded by walls on all four sides and may be located on grade or on aroof. However, it is important to note that the artificial formation should never beviewed as a satisfactory alternative to losing nature which should be preserved at allcosts. Figure 2.11: Courtyard is surrounded by walls on all four sides2.6 Plants in Urban Area Plants in an urban are mentioned to be able to provide benefits in the form ofenvironmental, social, financial and aesthetic value (Wong and Chen, 2009).Furthermore, it provide many valuable ecosystem services: they reduce energyconsumption, trap and filter storm water, help clean the air by intercepting airpollutants, as well as help in the fight against global climate change by sequesteringcarbon dioxide (Kelaine et al., 2008). Jonathan (2003) mentioned that plants have likely had a big influence on CO2level in atmosphere. They were the main source of oxygen, as it is one of the products
  • 37. 22of photosynthesis and acted as a trap for carbon. It is also mentioned that the biggerland plants, have likely led to a further increase in CO2 uptake. Plants also absorb gaseous pollutants for example nitrogen dioxide, andsulphur dioxide through leaf surfaces, intercept dust, ash, pollen, and smoke, releaseoxygen through photosynthesis, reduces emissions of pollutants from power plantsincluding volatile organic compounds (VOCs), as well as give shades which lowersair temperatures, reducing hydrocarbon emissions and CO2 levels (Wilhelim, 2008).Figure 2.12: Temperature decrease as plants help cool urban climates through shading andevapo-transpiration (Wilhelim, 2008) Plants can offer cooling benefits in a city through two mechanisms, directshading and evapo-transpiration. Figure 2.12 shows that temperature is lower in thearea with dense plantings. According to Wong and Chen (2009), the shading effect isquite straightforward and it very much depends on the density of plants. Peoplenormally have no quantitative sense of plants’ evaporative ability. The temperaturereduction can benefit individual building as well as the urban environment. Plants absorb water through their roots and emit it through their leaves, andthis movement of water is called transpiration. A large tree can transpire 40,000gallons 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, alsooccurs from the soil around vegetation and from plants as they intercept rainfall onleaves and other surfaces. Together, these processes are referred to as evapo-transpiration.
  • 38. 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 airtemperatures. Figure 2.13 shows plants take water from the ground through their rootsand emit it through their leaves, a process known as transpiration. Water can alsoevaporate 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 anyspecies can be considered truly typical (Treshow and Anderson, 1989). The mostfamiliar include the coniferous and deciduous trees, shrubs, vines and grasses. Thegeneralized plant structure consists of root and shoots which made up of the stem andleaves. Leaf is the principal photosynthetic organ of the plant and mostly has apigment called chlorophyll. Plants also have stomata. A stoma is a pore, found in theleaf and stem epidermis that is used for gas exchange.
  • 39. 24 It is clear that plants need sunlight, water and CO2 to do photosynthesis.However, the changes of atmospheric CO2 concentration and temperature will haveimportant consequences to plants. According to Jonathan (2003), plants usuallyprevent themselves from losing too much water in the drying air, but they also need totake in CO2 in order to photosynthesize. A plant could easily coated themselves withwaxy layer to prevent water lost however this would almost totally prevent CO2 fromgetting into its leaves, and it would be unable to grow. Therefore plants have tobalance of between gathering CO2 in order to photosynthesize and avoiding death bydehydration. Jonathan (2003) explained that when plants have plenty of water, thestomata let CO2 in. If more water added around the roots of the plants, they will takeup more CO2 and photosynthesize. If instead more CO2 added to the air around theplants, 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 throughcarbon sequestration. Unfortunately this solution is not that simple. Plants and treesnormally grow slowly. Although the potential to sequester carbon is fairly large, theactual 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 foliageprovide the most benefits (Laurie, 1979).2.6.2 Photosynthesis The only natural mechanism known to utilize atmospheric CO2 isphotosynthesis by green plants. Photosynthesis is the conversion of solar energy intochemical energy, which is stored in sugar. The chemical reaction that takes place insimplified form is as below. It shows that water, carbon dioxide and solar energy areconverted into glucose and oxygen. 6H2O + 6CO2 + sunlight C6H12O6 + 6O2 (2.6)
  • 40. 25 The photosynthesis process creates carbohydrates that are distributed to thevarious plant components, resulting in the growth of plants attributes. Withoutphotosynthesis there would be no animal life, no oxygen in our atmosphere, no fossilfuel reserves and according to Treshow and Anderson (1989) it would perhaps did nothave 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 aplant leaf (Figure 2.14). It is performed in two separate reactions: light reactions anddark reactions. The light reactions occur during the day. When light strikes a pigmentcalled chlorophyll, electronic energy is excited and manipulated in a chemical processcalled photophosphorylation, where energy is produced in the form of adenosinetriphosphate (ATP). This ATP produced by the light reactions fuel the synthesis ofglucose (sugars), which is accomplished during the dark reactions. Through achemical process called the Calvin cycle, carbon dioxide is harvested and manipulatedto produce glucose molecules (Mohammad, 1997).
  • 41. 26 According to Xu and Shen (1997), midday depression of photosynthesisoccurs in many plants. It is a common phenomenon. Xu and Shen (1997) mentionedthat under natural conditions there are two typical patterns of photosynthetic diurnalcourse (Figure 2.15). One is one-peaked which net photosynthetic rate increasegradually with the increase in sunlight intensity in the morning, reaches its maximumaround noon, and then decreases gradually with the decrease in sunlight intensity inthe afternoon. Another in two-peaked where there are two peak values of netphotosynthetic rate, one in late morning and another in late afternoon with adepression 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, airtemperature, air humidity, soil water status and carbon dioxide concentration in theair. In general, the two-peaked diurnal course of photosynthesis occurs on clear daywith intense sunlight, while the one-peaked diurnal course occurs on cloudy days with
  • 42. 27weak sunlight (Xu and Shen, 1997). Naturally, it is assumed that the middaydepression is caused by intense light. To some extent midday depression is related to high air temperature becauseof enhanced CO2 efflux from respiration and/or photorespiration. Midday depressionof photosynthesis is also often accompanied by a decreased CO2 concentration aroundnoon (Xu and Shen, 1997). Decreased CO2 concentration is an important ecologicalfactor leading to midday depression.2.6.3 Plants and Carbon Dioxide Plants excel at storing carbon. As a consequence, the photosynthesis processin which ambient CO2 is used to create sugars and carbohydrates, plants sequestercarbon (Bhatti et al., 2006). Because of these unique characteristic, plants are themain living organisms on Earth that have the capacity to mitigate the increase in CO2concentration 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 upcarbon. This relied on taking comprehensive measurements of the CO2 concentrationaround 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 thoughthe forest ecosystem is also respiring during the day, in daytime there will normallybe more photosynthetic uptake of carbon than carbon release from respiration.Followed by night-time assessment to measure how much the CO2 concentrationaround the forest has been raised at night relative to the background level in theatmosphere (Jonathan, 2003). However, it is mentioned that this approach is compelling but also veryambitious. Various studies show strange result and there is nagging question ofwhether these studies might contain errors. It is pointed out that a lot of important
  • 43. 28processes occur in forest such as tree falls, landslides and droughts which might affectthe data. Even though it remains an open question as to how much it can really teachus, it is nevertheless scientifically important.2.6.4 Plants and Atmospheric Pollutant Atmospheric pollutants are transported to vegetation from their source bywind and turbulence (Fowler, 2003). Wind spread pollutants over landscape andtransport pollutions from sources and source area. The transport of gases from theatmosphere to the terrestrial surfaces is by turbulent transfer, which is generated byfrictional drag by terrestrial surfaces on the wind. Thus the nature of the surfacestrongly influences rates of transfer. Fowler (2003) mentioned that the aerodynamically rough surfaces of forestsand 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 muchgreater over forests than over short vegetation for example grassland. Figure 2.16shows that the rates of deposition of pollutant gases and particle depend on both theturbulent transfer to the surface and processes at the surface which determine theuptake of gases or capture of particles. According to William (1990), plants in general have the function as sinks forgaseous pollutant. The gases transferred from the atmosphere to vegetation by thecombined forces of diffusion and flowing air movement. Once in contact with plantsgases may be bound or dissolved on exterior surfaces or be taken up by plants viastomata. Thus shows that plants have the capability not only to enhance the urbanatmosphere but also act as a functional companion that acts on pollutant towards abetter urban living.
  • 44. 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 canprovide quantitative benefits, in the form of financial returns, as well as qualitativeenvironmental, social and aesthetic benefits.a) Environmental Benefits Plants offer cooling benefits in an urban area through two mechanisms, directshading and evapo-transpiration which has been explained earlier. As a result, notonly shaded hard surfaces in the urban area but also the ambience can experiencesrelatively low temperatures. The temperature reduction can benefit not only individualbuildings but also the urban environment. Furthermore, plants have been widelybelieved to be effective scavengers of both gaseous and particulate pollutants from theatmosphere in the urban environment (Miller, 1997). They can improve the air qualityby filtering out airborne particles in their leaves and branches as well as by absorbinggaseous pollutants. The low surface temperature caused by plants may also reduce therisk of forming low atmospheric ozone which is the primary component of smog.
  • 45. 30 However, vegetation does not always respond positively to pollution stress.Air pollution has a negative impact on plant metabolism. A reduction ofphotosynthetic capacity or even the appearance of chlorosis or necrosis can beobserved in plants which are planted in a heavily polluted environment (Coleman etal., 1995). Planted surface has the ability to retain storm water and it is a practicaltechnique for controlling runoff in a built environment. Environmentally, this translateinto benefits such as reduction of the surface contaminants in the rainwater, reducedoccurrence of soil erosion and improved well-being for aquatic animals and plants.b) Economic Benefits Economic benefits are very much related with the environmental benefitsbrought by plants in an urban area. The ability of surface covered with vegetation toretain storm water and lower peak runoff can help in reducing the extent of stormwater drainage infrastructure. This has been applied by employing smaller stormsewers, which in turn saves construction and maintenance costs of the town’sdrainage systems. Plants introduced around buildings can improve construction’sintegrity by lessening the weather effect (Wong and Chen, 2009). Energy saving are another significant economic contribution brought by plantsin the urban area. Not only tree shading but also strategically placed plants aroundbuildings can achieve energy savings. In Singapore, a hospital has managed to cut itswater and electricity bills by SGD800, 000 in one year after adopting green roofs andother 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 thatmany urban dwellers feel for the natural landscape. Vegetation can provide visualcontrast and relief from a highly built-up city environment. Plants also give asignificant psychological sense of accessing Mother Nature in concrete jungles where
  • 46. 31buildings and pavements dominate the urban area. Furthermore, vegetation provideselements of natural scale and visual beauty. In addition, incorporating plants aroundbuildings can also offer visual interest and relief to plain walls and roofs and separatethem from the obtrusive hard edges of surrounding buildings (Figure 2.17). Unsightlybuilding 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 buildingsd) Social Benefits Plants can fulfil various social functions in a built environment. Green spacein urban area provide places for playing, sport and recreation, meeting, establishingsocial 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
  • 47. 32in the neighbourhood (Wong and Chen, 2009). Urban area can be made livelier byproviding ample amounts of accessible outdoor recreation or amenity space. It has also been proved that visual and physical contact with plants can resultin direct health benefits. Ulrich and Parsons (1992) studied the psychological effectsof plants on humans and revealed that plants can generate restorative effects leadingto decreased stress, improve patient recovery rates and higher resistance to illness.Besides their psychological impacts, plants have other physical impacts whichbenefits human. The air cleansing quality of plants has direct respiratory benefits forpeople who suffer from asthma and other breathing ailments, and directly lowerssmog and other forms of air pollution. The potential of greenery to lower hightemperature can reduce heat-aggravated illness, which directly and indirectly reducelife expectancy of human beings and death among the city population.
  • 48. CHAPTER 3 METHODOLOGY3.1 Introduction This chapter explained thoroughly the procedure of works as to achieve theaim and objectives of this study. Detailed processes and method are illustrated whichfocus on types of data collection, types of equipment used during data collection, andmethods used to calculate plants volume.3.2 Data Collection and Sampling Method Data collection is taken during clear sunny day and was collected in twocategories. In the first category, data collection is done in a green space. The greenspace 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 bywalls on all four sides. The selected courtyard is located enclosed in the centre of school buildingswith 12298cm2 area size. It is done during school holiday as it will be unoccupiedwhich help in controlling the gases uptake and discharge. The courtyard conditionswere differentiated with four types of plants volume (Figure 3.2). Details of the
  • 49. 34courtyards are presented in table 3.1. Data collection for courtyard’s condition is donein 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
  • 50. 35Figure 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
  • 51. 36Figure 3.3: The controlled environment conditions were differentiated with three typesof plants volume3.3 Parameters Parameters that involved in this study are Carbon Dioxide (CO2), Oxygen(O2), Carbon Monoxide (CO), Temperature, and Relative Humidity. These werechosen since it is related with the balanced condition of gases in atmosphere andinfluences the outdoor thermal comfort.3.4 Equipments Four types of equipment used during data collection. The equipment used toacquire the temperature data and relative humidity is Multi-detector LUTRON 4 in 1LM-8000, a product of Taiwan. The concentration of carbon monoxide is detected byGray Wolf Direct Sense PPC Kit made from Germany. Carbon dioxide is detectedusing TSI 7515 IAQ-CALC Carbon Dioxide Detector, and oxygen data is collectedby MSA Altair 4 Multi-Gas Detector (Figure 3.4). All the equipment is located in thecenter spot during data collection for both the courtyard area and the air-tight glassbox.
  • 52. 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 Kit3.5 Methods Used to Calculate Plants Volume There are several methods that can be used to calculate plants volume forexample Urban Forest Effects (UFORE) (David et al., 2005), and Street TreeResource Analysis Tool for Urban Forest Managers (STRATUM) (Wong et al.,2006). In this study, the plants volume was calculated using the consideration ofestimated plants crown shape seen as a ratio to the cylinder (Gunther, 2008) (Figure3.5). 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 thisstudy is ornamental plants which usually used in the urban green space.
  • 53. 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 andobservations, the data collected was analysed by plotting graph according to theparameters involved and statistical analysis is carried to clarify and illustrate the resultgain from the method used.
  • 54. CHAPTER 4 RESULTS AND ANALYSIS4.1 Introduction This chapter discussed on the results and analysis achieved from the datacollections. The discussion related with the literature review, method used and headedfor findings in conforming to the objectives of the study. The results of this studyfocused on carbon dioxide, oxygen, temperature and relative humidity as well as finaldiscussion based on result from all conditions. Carbon monoxide is negligible in thisstudy 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 tothe imbalance between atmospheric oxygen (O2) and CO2 (Mohammad, 1997). Theonly natural mechanism known to utilize CO2 is photosynthesis. Figure 4.1 shows thetrend of CO2 changes for different courtyard conditions that are conditions C1 noplants or grass, C2 plants only, C3 grass only, and C4 plants and grass. C1 has higherCO2 level with average 502ppm almost 43% higher than normal CO2 concentration inambient air which is 350ppm. This is because according to Wisconsin Department ofHealth Services (2008), CO2 concentration in normal outdoor air level is 250ppmuntil 350ppm.
  • 55. Peak photosynthesisFigure 4.1: Comparison of carbon dioxide concentration according to different courtyard conditions 40
  • 56. 41 This is followed by C2 result with average concentration of CO2 of 431ppmthroughout the data collection. Meanwhile it was recorded below 350ppm during C3and C4 with average 331ppm and 324ppm respectively. Thus this shows that CO2reduction in C4 condition is higher than the other conditions. This is because the C4condition has highest area coverage with vegetation and plant volume. However, oneof the interesting finding is even though the plant volume in C2 condition is higherthan C3, the average CO2 concentration of C3 condition is much lower withdifferences of 23% compare with C2. This might be due to different area covered withvegetation which is higher in C3. Even though C3 has less plants volume than C4, from figure 4.1 shows thatthe CO2 uptake for C3 trend is quite similar to C4. This illustrate that the area sizecovered with vegetation is crucial in providing significant changes for CO2 trend.However, there is still different in CO2 concentration (p < 0.05) as enclose inAppendix B Table B1. Nevertheless C4 has the highest CO2 reduction withdifferences of 3% compare to C3 condition since it has a higher plants volume withall ground area covered with grass. This also can verify that the volume of plants isimportant in assuring CO2 reduction. In addition, it agreed with the findings byFowler (2003) which indicate rates of transport of gases from the free atmosphere tothe surface are much greater over dense and high vegetation than over shortvegetation such as grassland. The carbon-reduction phase of photosynthesis requires light. Consequently,Figure 4.1 shows CO2 reduction happened particularly around 10:30am until 14:00pmwhen most of the area received full solar intensity. This is because the site for datacollection 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 theday (Figure 4.3 and Figure 4.4). However, C1 shows CO2 increment at that timesince no photosynthesis process occurs.
  • 57. 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 04:00Figure 4.4: Different solar intensity during evening and night
  • 58. 434.2.1 Day and Night Comparison The carbon-reduction phase of photosynthesis requires light and will eitherbarely active or totally inactive in the dark (Vivekanandan and Sarabalai, 1997). Thisis 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 asthe sun falls. During night the photosynthesis process is barely active and plants usageof CO2 has decreased. Plants utilize CO2 at night as there is no sunlight energy whichallows photosynthesis process to happen. During day time from 8:00am till 19:00pm, the average CO2 concentration isfor C3 and C4 condition is 315ppm and 306ppm respectively. While during night timestarting from 19:00pm, the average CO2 concentration for C3 and C4 condition is343ppm and 338ppm respectively. The difference is only 1% for the average CO2concentration for C3 and C4 condition. C1 CO2 concentration reduces from thehighest peak that is 585ppm to 430ppm during 5:30am. This is 26% differences andmight be due to the absent of sunlight energy. Significant differences of C3 and C4 condition throughout the day for CO2concentration (p < 0.05) as enclose in Appendix B table B2. Thus shows that duringthe night time the present of plants either with high or low volume is not obvious tothe CO2 changes. However this might be due to the plants conditions used in thisstudy which is low plantings.
  • 59. Figure 4.5: Comparison of carbon dioxide concentration during day and night 44
  • 60. 454.2.2 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 asreference. Therefore, on this study it is found that the oxygen reading is typically20.8% and was set as the guideline in comparing any changes throughout the study.
  • 61. Peak photosynthesisFigure 4.6: Comparison of oxygen concentration according to different courtyard conditions 46
  • 62. 47 Plants were mentioned to release oxygen through photosynthesis (Wilhelim,2008), and this process requires light which evidently shows on figure 4.6 whichillustrate the C4 and C3 data fluctuate. From Figure 4.6 shows C2 oxygen reading ismostly constant except during noon. This most probably due to the small area coveredwith 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 ofplants in C3 thus less CO2 uptake needed for photosynthesis process. Substantialdifferent of all conditions (p < 0.05) has been pointed out as attached in Appendix BTable 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 becausefrom 17:00pm till 6:30pm no changes of O2 data. Compare with day time, the O2 dataduring night time is not significant and as well as no sign of O2 reduction. This isbecause 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 hasbeen lost in the last 200 years is much less than one-thousandth of the oxygen in theatmosphere.
  • 63. Figure 4.7: Comparison of oxygen concentration during day and night 48
  • 64. 494.3.2 Result from Controlled Environment Oxygen result from controlled environment is negligible as the data has nochanges in every condition. This might due to loss of photosynthetic O2-evolutionactivity 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 C4condition due to high differences. Substantial differences have been pointed out inAppendix B Table B1 and Table B3. Figure 4.8 and figure 4.9 clearly show that whenthe Oxygen (O2) data fluctuate, it is consistent with Carbon Dioxide (CO2) readingsthat decreased during peak sunlight intensity. At time the O2 readings are back to20.8%, the CO2 started to increase with time. It shows that CO2 level increase sincevegetation no longer utilizes CO2 for photosynthesis at night.Figure 4.8: Comparison between carbon dioxide and oxygen concentration in courtyardwith grass and plants (C4)
  • 65. 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 courtyardwith grass only (C3)
  • 66. 514.5 Carbon Dioxide and Temperature The CO2 and temperature trend resulting from C1 agreed with the figures byJonathan (2003) and Al Gore (2006) which indicate that when there is more CO2 inthe atmosphere, the temperature increases (Figure 4.10). However, the trend changewhen the vegetation is present and photosynthesis process occur. Even though thetemperature trend in C2 is similar with C1, it drops below average a few hours earlierand the CO2 also decrease almost 14%. Substantial differences has been pointed out inAppendix B table B1 and table B4. From Figure 4.10, it shows that C2 condition has no significant changes ofCO2 data. This might be due to high temperature which affects plants growth,metabolism and productivity. As mentioned before, elevated temperature leads to lossof photosynthetic O2-evolution activity and limiting photosynthesis (Dubey, 1997).Differences of both C2 and C1 condition in temperature value (p < 0.05) has beenpointed out in Appendix B Table B5. This shows that even small number of plantvolume is allocated, there is differences in temperature and CO2 concentration whencompare to deserted area. From Figure 4.10 also indicate that the C4 temperature drops 2 hours earlierwhen compare to C3. During 11:00am till 15:00pm, the temperature value for C3 ishigher when compare with C4. As discussed earlier, plants can offer cooling benefitsthrough two mechanisms that are direct shading and evapo-transpiration. In this case,the plants selected are small plantings therefore indicate that by evapo-transpirationalone can provide significant changes to the outdoor surroundings. It is believed that C3 temperature drops rapidly compare to C4 because in C4the plants upright and vertical volume trap heat which make the temperature changegradually. Similarly to C2 when compare with C1 which indicate the temperaturedecrease slowly and the data trend appear jagged.
  • 67. (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
  • 68. 53 Based from Figure 4.10, Figure 4.11 is illustrated to shows that solar energyreflected by earth surface and absorbed by vegetation in all four condition thus, givingdifferent result in both temperature and CO2 reductions. CO2 trend in C4 and C3shows significant drop compare to C1 and C2. According to Kusterer (2007), thepercentage 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, about30 percent of incoming solar energy is reflected back to space. Rain forests andvegetation surface reflect only a small portion of the Suns energy. However, desertswith no plants have high albedos (40%); they reflect a large portion of the Sunsenergy. Figure 4.10 also illustrate that in C4 condition, CO2 decrease below 300 for 8hours while C3 for 2 hours. Even though C4 and C3 has similar area size coveredwith vegetation, this differences is due to higher plants volume which requires higherCO2 uptake for photosynthesis process (Figure 4.10). Differences of both condition intemperature 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
  • 69. 544.6 Temperature and Relative Humidity An average temperature in Malaysia is between 23.7ºC to 31.3ºC and theaverage relative humidity throughout a day between 67% until 95% (Hussein andRahman, 2009). Thus shows that the maximum acceptance temperature is 31.3 ºC.However, it is mentioned that temperatures above 30°C are usually considereduncomfortable (Wang and Wong, 2007). Furthermore, changes in temperature oftenlead to quite significant alterations to the relative humidity since air can hold morewater vapor at higher temperature, relative humidity values decrease as temperatureincreases (Godish, 2004). This is clearly shows in Figure 4.12. Furthermore, it is mentioned when temperature was 31°C and relativehumidity 69%, a wind speed of 5 ms- l or more is necessary to overcome heatdiscomfort (Pakar, 1985). However, during this study, the wind speed is unnoticeablewhen measured using Multi-detector LUTRON 4-in-1(Figure 3.4) which most likelybecause the courtyard is surrounded by walls on all four sides. Thus, shows that therelative humidity in this type of green space is preferred to be above 70% to provideoutdoor thermal comfort. Figure 4.12 shows the significant differences of C1 and C4 for both relativehumidity and temperature. With differences of 47% increase for relative humidity and12% decrease for temperature, staying in the C1 in the noontime is considered veryuncomfortable compared to C4. Temperature in C1 condition rose above 30°Cbecause there is no photosynthesis process which leads to CO2 accumulation. CO2molecules known to absorb heat energy and in addition the heat builds up due tobuilding’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 introducingonly grass to the area, the thermal condition has been improved. Even though this typeof planting did not provide shade to the area, it still helps reducing the surroundingtemperature.
  • 70. Full sunlight intensityFigure 4.12: Comparison between temperature and relative humidity according to different courtyard conditions 55
  • 71. 56 C1 and C2 average temperature differences are only 2% even though there areplants 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 bedue to less area covered with vegetation thus less incoming solar energy beingabsorbed by plants. However, C1 and C2 average relative humidity differences is23%. This is considered high difference which shows that being in the C2 condition ispreferable 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 toC3 condition, C3 result for both relative humidity and temperature is better. C2 hasaverage temperature of 32.4 °C and average relative humidity of 61.8%, while C3 hasaverage temperature of 29.7 °C and average relative humidity of 70.7%. Theseindicate that being in the C3 condition is much more comfortable compare to in C2condition. Even with low plant volume, increasing the area size covered with greeneryin 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 thermalcomfort in urban area. C4 has average temperature of 29.1 °C and average relative humidity of73.4%. When compared with C2, there are 15% differences in relative humidity and10 % changes in temperature. Thus shows that by increasing the plant volume bothhorizontally and vertically as shown in Figure 4.11 would help in increasing thethermal comfort even if the plants did not offer shade. This might also indicate that byproviding plants with shade will help increase the thermal condition significantlysince 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 from13:30pm 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 addingmore plants volume helps in improving the thermal conditions.
  • 72. 574.6.1 Day and Night Comparison From Figure 4.13 show that being in all C1, C2, C3 and C4 conditions at nightis somehow tolerable. This is because almost in all condition the temperature ismostly under 30°C. This might be due to the absent of sunlight. It is because one ofthe important factors of atmospheric warming is the incoming solar energy which isthe ultimate energy source for all atmospheric processes (Bhatti et al., 2006). Heat, according to Treshow and Anderson (1989), ultimately derived fromsolar 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 heatreleased by the hard surface of the building and soils. Unlike the C1, the vegetation inC2, C3 and C4 reflect only a small portion of the Suns energy. Instead the vegetationuses this energy to produced food. In C1 condition, the heat is reflected and absorbsby the hard surface and it continued released heat at night. This has cause the heatexchange near the surface which leads to high temperature and relative humidity. Relative humidity trend at night time shows significant reduction for all fourconditions. C1condition shows increase of relative humidity around 21:00pm. UnlikeC3 and C4 which started to increase after 14:30pm when the area no longer receivedfull sunlight intensity (Figure 4.12). C2 shows changes and increase of relativehumidity trend starting from 17:00pm. This is when the area a fully shaded by thebuilding blocks from direct sunlight. However differences of all conditions in relativehumidity value (p < 0.05) has been pointed out in Appendix B Table B7. Thus showsthat by implementing vegetation to the area help increase the relative humidity andthis 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 willreduce the rate of evaporation of moisture from human body, especially in thelocations where the lack of air movement is experienced.
  • 73. Figure 4.13: Comparison between temperature and relative humidity during day and night 58
  • 74. 594.6.2 Result from Controlled Environment Table 4.2 illustrate that the box with grass (B3) is warmer however, figure4.14 shows that the solar energy absorbed by vegetation in B3 compare with B1 thatis empty thus absorbed less solar energy which turn into heat. The B3 has highesttemperature because CO2 molecules released by grass absorb heat energy, as well aswith the present of the grass which trapped in the box causes it to be warmer (referfigure 4.14). Unlike plants in B2 which give off water vapor through the process oftranspiration which help in lowering the temperature. Even though grass in B3 didundergo transpiration process due to the volume size the result is not perceive. B2shows temperature decrease 2% compare with B1. From this shows that by increasing12% plants volume help in reducing 2% temperature in average. Figure 4.14 showsthat the solar energy absorbed by vegetation compare with B1 that is empty thusabsorbed 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 forthis study did not give shade thus by implementing plants with shade would reducemore temperature value. Secondly, even in the trapped condition where heat cannot bereleased from the glass box, the plants activity has helped modified the temperaturethus shows that plants are important in improving the urban thermal environment.
  • 75. 60 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 Table 4.3 shows B2 has high relative humidity percentage due to the highvolume size of plants and also high transpiration or evaporative cooling of the plantswhich 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 thecondition inside the box appear suffocating. This shows the side effect of high relativehumidity which will offset thermal comfort especially when the temperature is highand no wind to overcome heat discomfort. Furthermore, both the B2 and B3 showsincrease value of relative humidity. Table 4.3: Results shows relative humidity differences in various conditions No Plants Plants Grass Time/Condition (B1) (B2) (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 - 44% 13% in percentage (*Unit: RH %)
  • 76. 61 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 From the observation, even though the grass did increase 13% of relativehumidity however the grass in B3 died the next hour due to intense sunlight and hightemperature (refer Table 4.2). From the temperature and relative humidityobservation, it illustrate that by increasing 10% of the plants volume, the thermalenvironment 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 whichusually has high temperature requires green space with high plant volume. This isbecause, even though the plants did not give shade, when it has more volume, it canhelp modify the outdoor thermal comfort and give balance between temperature andrelative humidity.
  • 77. CHAPTER 5 CONCLUSION5.1 Conclusion Increasing plants volume has shown potential in improving air quality andoutdoor thermal conditions. The changes of carbon dioxide, oxygen, temperature andrelative humidity are found to be significant according to various plants volumeallocation. However, the size of horizontal area is much more crucial and whencompliment with vertical plants volume indicate significant CO2 reduction andphotosynthetic O2-evolution. From this study, result shows that by increasing theplants 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 aremuch greater over vegetation with vertical volume than over short vegetation such asgrassland. With this it shows that green space size in urban area should be reservedmore and the plants within it should have more volume. Consequently this could helpimproving the urban surrounding and thermal condition. Plants certainly help promote outdoor thermal comfort because even thoughthe temperature in the urban area is high, plants selection with more volume andheight help cools down the surrounding by transpiration. This can be perceived evenmore 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 increasesmore than 20%, the thermal comfort can still be achieved. Plant can give balance
  • 78. 63between temperature and relative humidity thus helps modify the outdoor thermalcomfort. Therefore this shows that capability of high plants volume in improvingoutdoor ambient air and thermal improvement has been identify. Furthermore, plants and trees having thick canopies and dense foliage providethe most benefits. Therefore, when proposing and implementing urban green spaceespecially 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 viewedas a satisfactory alternative to losing nature. Natural environment and native plantsare best to be preserved at all costs. Even though the only natural mechanism known to utilize CO2 isphotosynthesis, it is important to consider that relying on green space and plantsvolume alone will not formulate a better environmental quality. Nevertheless it ispartly as a function that contributing towards enhanced outdoor environment andmaintenance of ecological system in urban area.5.2 Recommendation There are several suggestions that recommended to be implemented whendesigning for the outdoor urban green space as to improve the ambient air and thermalcondition: (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.
  • 79. 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.
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