a system dynamics model of sustainable urban development

Asian Pacific Planning Review Vol. 4, No.1, 2006, December

www.tiup.org.tw

Asian Pacific Planning Review, Vol. 4, No.1, 2006, December 29

A System Dynamics Model of Sustainable Urban Development: Assessing Air Purification Policies at

Taipei City Mei-Chih Chen*, Tong-Po Ho* and Chiou-Guey Jan**

*National Cheng Kung University, Taiwan**Providence University, Taiwan

Received 29 July 2005; received in revised form:5 May 2006; accepted 7 June 2006

Abstract

A sustainable city demands a balance among economic, social and environmental concerns. The method of attaining a balance depends on the specific situation of a city. The development of urban sustainability involves several complicated problems, including externalities, public goods, the accumulative effects of long-term efforts, cross-sectoral coordination, and conflict management policies. Market mechanisms alone cannot be relied upon for achieving sustainability; instead, specially designed strategies and policies are generally required. This investigation examines alternative sustainable development policies for air purification in Taipei, a high density city. The system dynamics method is employed to analyze the causal relationships of air pollution problem primarily resulting from transportation and relating to the complex structure of urban development. Simulating and comparing the air purification effects of green land preservation and public transportation facilitation policies in Taipei, Taiwan, demonstrates that the green land preservation policy which previous was paid less attention appears possibly superior to the public transportation facilitation policy, which previously was more popular for air purification policy.

Keyword: Air purification, sustainable urban development, green land preservation, system dynamics, simulation

analysis.

E-mail:[email protected]

A System Dynamics Model of Sustainable Urban

30 Asian Pacific Planning Review, Vol. 4, No.1, 2006, December

Mei-Chih Chen, Tong-Po Ho and Chiou-Guey Jan


I. Introduction

Approximately 70% of the world’s populations currently live in urban areas, and urbanization is still continuing. Urban development undoubtedly brings economic benefits, but also causes environmental pollution. The major reason for ecosystem deterioration is modern ways of living and production (Davidson, 2001; Hawken, 2000; Miller, 2004). Therefore, how to restore good styles of human living and production is important for sustainability. Martell (1994: 47) stated: “Sustainability requires technical decisions about choice of technology, energy use and forms of production. Yet it also requires restrictions on growth, resource extraction and pollution and implies radically changed social lifestyles and values…, …which touch on issues to do with consumption, community and economy…” Inadequate techniques for pursuing economic growth frequently lead to ecosystem destruction. Sustainability means maintaining a good “ecological balance”. Stephen Wheeler (1996: 55) stated: ‘Sustainable urban development’ seeks to create cities and towns that improve the long-term health of the planet’s human and ecological system. Moreover, Campbell (1996: 297-8) stated that economic growth and efficiency, social justice and income equity, and environmental protection three conflicting principles that must be considered in sustainable urban planning. Restated, sustainable urban development requires balancing economy, society, and the environment. However, it is not possible to rely solely on market mechanisms for improving sustainability. Appropriate strategies and policies are critical to sustainability in urban areas.

It is well-known that environments can easily be destroyed due to its nature of non-market goods. Its value for sustainable urban development can not be accurately reflected by market mechanisms (Davidson, 2001). Only when people recognize the value of the environment can the environment be protected. However, people typically sacrifice long-term benefits associated with environmental resources for the sake of achieving short-term benefits. Subsequently, imbalances in the natural environment will emerge. For example, high population aggregation, massive use of motor vehicles and large losses of green land associated with urban development cause negative externalities such as air pollution. The main air pollutants are carbon monoxide (CO), particulate matters (PM-10), sulfur oxides (SOx), nitrogen oxides (NOx), lead (Pb), and non-methane hydrocarbons (NMHC), long-term exposure to which damages the human respiratory system (Environmental Protection Agency, 2004). Currently almost three million people die from air pollution annually around the world (Miller, 2004). Such serious and harmful situations resulting from urban air pollution should be tackled and solved.

Recently, policies for air purification are focused mainly on short-term approaches to reduce pollutants directly. Taking the NOx pollutant reduction as an example, solutions include such as

studying NOx emission sources (including fossil-fuel burning, anthropogenic, biomass burning, soil emissions, and lightning-produced), engine technique facilitation, photolysis in atmospheric circulation and photochemical reactivity of organic gases (volatile organic compounds (VOCs)), or by increasing use of public transportation etc. (Environmental Protection Agency, 2004; Hsu, 2000; Liu et al., 2005; Pargal et al., 2000; Russell et al.,1995; Wang et al., 2005; Zhang et al., 2003), but neglected the effects of increasing green land, which is a more effective means of air purification in the long term. Consequently, this study take the viewpoint of urban sustainable development and land use control to discuss long-term air purification effects of urban green land.

This investigation compares the air purification effects of green land preservation and public transportation facilitation policies for sustainable development. This study selected Taipei city, a highly population and high density city, as a study area. System dynamics were employed to design a dynamic simulation model for policy analysis. The remainder of this paper is organized into six sections. Section One is the introduction, which provides the study background, context and framework. Section Two then presents the characteristics of sustainable urban development. Next, Section Three describes why system dynamics is used as the study method. Section Four then presents the proposed model. Subsequently, Section Five demonstrates the simulation results of current trend and policy scenarios relating to air purification effects. Finally, conclusions are presented in Section Six.

II. Characteristics of Issues Related to Sustainable Urban Development

Sustainable urban development represents a balance among economic, social and naturally environmental development. Camagni (2001) stated that the key feature of urban sustainability is that: “It is necessarily based on a ‘weak’ definition of sustainability, as far as substitution between natural resources and human inputs is concerned” (Camagni et al., 2001: p.128)”. Claims of “strong sustainability” or “deep green” are inherently impractical; however, destruction of the natural environment as generally happens in developing countries for the sake of economic development also should not be permitted. In the real world, the problem is how to balance the conflicting demands of the economy, society, and natural environment. Dealing with this problem in an urban area requires first understanding the system structure of urban development; identifying actual problem areas where cities diverge from sustainable development, and then formulating appropriate policies and measures of environmental problems that exist in urban system structures. Particularly, it is important to realize the characteristics of urban sustainability, which are summarized below.





1.Urban sustainability is a form of externality and public goods

Improving environmental quality, spatial competitiveness, and social cohesion in a city requires the collective action of residents. The environmental, economic and social issues that sustainable development is concerned with are influenced by the inhabitants of a city. Namely, urban sustainability is a form of urban externality and public goods. Only when residents all agree on the value of pursuing urban sustainability, and consequently cooperate and work together, can they obtain mutual benefits. For example, air is a form of public goods, and air purification is a responsible action of urban residents. Air pollution will result when urban residents ignore the influences of their actions. Naturally, externalities and public goods are difficult for residents to sustain individually, and residents generally demand government assistance in maintaining environmental resources usage and management.

2.Urban sustainability has benefits mostly from a long-term view

Urban sustainability requires economic actors to consider environmental quality. However, doing this is difficult, simply because it increases costs. For example, due to the uncertainty of real estate market, most land developers prefer pursuing short-term benefits to long-term benefits. Alternatives that consider urban sustainability generally are more costly for developers, but do not benefit the developers. Despite the long-term benefits of urban sustainability, developers rarely consider these benefits, and generally avoid uncertainty and investment risk. Other behaviors such as consumption and production in urban areas have similar effects. Generally, urban environmental quality is highly vulnerable to damage.

3.Attainment of urban sustainability is a long-term cumulative process

Sustainable development means sustaining lives, production and environment in urban development. Unsustainable behaviors cannot be immediately identified in the short-term, but will gradually compromise the sustainability of whole urban development systems. The environment influences individual living and production behaviors in a step-by-step fashion, but when most people ignore the importance of environmental issues the system structure of urban sustainability gradually disintegrates. Therefore, urban sustainability requires governments to intervene in urban development stably and continuously to prevent dangerous living and production behaviors in urban areas.

4.Urban sustainability needs common efforts from many departments

The problem of urban development becoming unsustainable results partly from selfish departmentalism. Sustainable development requires cooperation or coordination among the departments of economic, social and naturally environmental development. However, in a specialized society, individual decision-making regarding urban development tends to focus on individual domain of discipline, but seldom considers how individual actions influence others. For instance, recent policies for controlling air pollution have mostly focus on reducing air pollutants directly, for example through facilitating the functions of public transport, highway systems, engine technologies, and so on (Environmental Protection Administration, 2000; Pargal et al., 2000). However, these policies are limited by being limited to transportation system management, and lack consideration of evaluation and planning involving other urban managerial departments.

In fact, policies such as facilitating the functions of public transit are not a catholicon that can completely substitute motor vehicle functions such as speed, convenience and mobility. Practical experience demonstrates that increasing the convenience of urban highway and traffic systems also increases the frequency of motor vehicle use, thus increasing air pollution problem. Therefore, potential remains for discussing air purification policies related to modifying urban air pollutants in direct or indirect ways whether transportation system management policies are appropriate for dealing air pollution problem. This study should explore in depth the characteristics and roots of the air pollution problem in multidisciplinary respects which relate to urban development, and should seek appropriate policies that can benefit the whole urban system.

III. Method

The problem of urban sustainable development results from urban people who only considering their own particular aims, but ignoring the long-term benefit of the community. However, the system structure of urban development possesses characteristics of long-term dynamic interaction among multidisciplinary departments. Therefore, the characteristics of urban system structure should be controlled for formulating appropriate policies and measures for problems involving urban sustainable development. Urban air pollution problems can be interpreted using a hierarchical structure with three main components: 1) Sustainable urban development vision, 2) Air pollution purification policy, and 3) Land use and management system. None of these components can be treated in isolation, and they interlock like links of





a chain (Jan, 2003). Furthermore, non-linear relations among these components, the slow and gradual process through which air pollution forms, and the various components at different levels of the hierarchy operate in a both independent and reciprocal fashion, thus increasing the complexity of problems of urban sustainable development. Therefore, reasoning regarding feedback causality and the task of preventing urban air pollution must address problems holistically, considering individual departments as components of an integrated whole, and maintaining a constant long-term focus (Ackoff and Pourdehnad, 2001). Unlike traditional econometrics research methodology, system dynamics (SD) provides a simple and practical technique for analyzing and simulating urban sustainable development.

The system dynamics philosophy is based on two underlying beliefs: 1) the behavior (or time history) of a system is principally caused by the system structure, through changing the system structure can improve system behavior; 2) the concept that systems can be understood most clearly in terms of their common underlying flows rather than in terms of separate functions. By identifying the integrating flows of materials and information in all systems, the flow structure orientation causes managers to cross subsystem boundaries naturally and further understand their interactions (Roberts et al., 1978). These holistic views are suitable for analyzing issues of urban sustainable development. Accordingly, the system dynamics makes five contributions to this study, as summarized below:

(1) By adopting a holistic approach to analyzing the complex system structure of urban development and its interlocking components (Jan, 2003; Sterman 2000), the root causes for making cities diverge from sustainable development can be identified.

(2) The concept of flowing interactions among urban subsystems is used to integrate their mutual conflicts and individual aims, which does not adapt to holistically benefit sustainable urban development. Guiding decision-making groups of urban development reason problems and make appropriate decisions. (Roberts et al., 1978; Sterman 2000).

(3) The system dynamics methodology employs dynamic computer simulation to program the mathematical model; the special table function and delay function offer appropriate methods for dealing with non-linear relations of components involved in urban development (Coyle, 1996; Jan & Jan, 2000).

(4) The strict logical operation and dynamic simulation of the system dynamics model can supplement the inadequate intuition and mental simulation capacity of urban planners. The system dynamics methodology is appropriate for sustainable urban planning problems that are long-term, dynamic, counterintuitive, and crucially, for which there is no widespread consciousness regarding intervention (Jan, 2003; Roberts et al., 1978; Sierman 2000).

(5) Urban air purification policies have difficulty in obtaining instant results. Therefore, impatient decision-making groups have poor awareness of their long-term effect of air

purification and thus easily lose the patience to support implementation of air purification policies. This situation demands a simulation model of system dynamics to illustrate the modifying effect of air pollution and help demonstrate the long-term development trend (Jan, 2003).

These five characteristics help demonstrate land use trends in a long-term process of urban development, help to realize the complex structure of interlocking components in urban systems, and easily deal with non-linear and dynamic relations of components involved in urban development. Consequently, fundamental conflicts between the aims of sustainable urban development and the modification of the air pollution problem can easily be interpreted definitely, and key air purification policies then can be explored.

IV. Model

“System behavior primarily results from system structure.” is one of the main philosophies of system dynamics (Jan, 2003; Roberts et al., 1978). For understanding how serious the urban air pollution will become, this study develops a system dynamics model to simulate the consequences of economic development guiding land development. This study compares the effects of public transportation facilitation and the green land preservation policies that influence air quality. Taipei city in Taiwan was selected as a case-study for discussing how to deal with air pollution problems in urban development. The simulation time in this study is 1969-2050. For illustration the long-term accumulative influences from people’s activities that result in urban air pollution problems, the prime air pollutant selected for simulation is NOx, which is not only discussed in research on air pollution, but also in absorption research dealing with plants (Environmental Protection Agency, 2004; Hill, 1971; Jensen and Pilegaard, 1993; Pargal and Heil., 2000; Sung et al., 1998).

Although air pollution problems discussed in this study are emphasized on the mobile pollutants, the immobile NOx emissions have also involved in the calculation of NOx annual emissions remnant in Taipei city in the processes of SD modeling and simulation. The calculation of NOx emissions takes account of the NOx emission amount of Taiwan, ratio of north Taiwan air area, and ratio of immobile pollutants amount of Taipei city that measured by Taiwan EPA (Institute of Transportation, Ministry of Transportation and Communications,, Taiwan, R.O.C. (MOTC), 2006; TEPA, 2000). Besides feedback loops and the whole quantitative simulation model, this study briefly explains how to deal air pollution problem with key variables for details as follows:





1.Causal relationship between urban development and air pollution

Urban development policies generally focus on economic benefits and urban functions such as housing, employment, and transportation (Stearns and Montag., 1974); but ignore the importance of goods with no market value, such as air quality. Therefore, from a long-term perspective, government control of land use seldom restrains the real estate market during urban development; instead government provides a large supply of land for development and public facilities to satisfy land developers and investors. The result is that urban populations increase as more people are attracted into cities by the increased employment opportunities provided by developers and investors.

This pattern of urban development relates to land development, population growth, urban traffic and environmental quality. System behavior demonstrates that land development tends to benefit the urban economy. The tendency for positive development to result from land development and population growth resembles a positive feedback loop of urban development, as shown on the left side of Fig. 1. Consequently, population growth also increases the number of active motor vehicles in urban areas, and the emissions of these vehicles gradually result in a long-term accumulation of polluted air and thus reduce urban air quality (Miller, 2004), as indicated by the negative feedback loop shown on the right side of Fig. 1.

Population

Urban LandDevelopment

+Air

Pollution

-

+

Number ofVehicle+

+

EconomicActivities+

Delay

PollutantEmission

+

EconomicDepartments

EnvironmentalDepartments

Figure 1. Feedback loops related to urban economic departments and environmental departments

Air pollution is not only a negative externality in terms of its environmental effect by pursuing urban economic growth in urban development, but also damage the health of residents and also their intention to live in cities (Occupational and Environmental Health Protection of the Human Environment World Health Organization, 2001). Following long-term urban development, these circumstances influence urban population and land developer investments, and finally will cause negative feedback to urban sustainable development.

2.Growth and decline of green land air purification capacity

Land development and urban growth can undoubtedly bring short-term economic benefits to urban residents, but long-term environmental benefits are lost by exhausting green land for the sake of urban growth. Lack of green land easily leads to “the urban heat island effect” (Miller, 2004). This effect involves reduced air purification capacity. This effect occurs in populated cities and leads to the discharge of polluted fog by motor vehicles, then becomes an air pollution problem (see Fig. 2), particularly in a basin landform city like Taipei, where the problem can become quite serious. Furthermore, by the simplified diagram of the mathematical simulation model on Fig. 3, we assume the dynamic relationship between the air purification capacity of green land and the influenced air quality in urban area.

Population


+

Number ofVehicle+

Green Land

-

Air Pollution-+-

+

Delay

EconomicActivities

PollutantEmission

+

+

Air PurificationCapacity

+

+

Employees NotLive in City

VehiclesOutside City

+

+

+

+

Figure 2. Feedback loops related to the growth and decline of green land urban air purification capacity





Green landGreen Land

Increased RateGreen Land

Decreased Rate

Park, Green Fieldand Plaza Land

Urban Developedfor Building Land

Number ofActive Vehicle

Building LandIncreased Rate

Building LandDecreased Rate

PollutantEmission

Air Pollution +

Urban Land Planningfor Development

+


+

-

+

+

+

+

Indirect InfluenceDemand forEmployment

+

Delay

+Population

+

+


+

PopulationDecreased Rate

PopulationIncreased Rate

+

+-

Figure 3. A simplified diagram of the mathematical simulation model with the principal variables and relationships important to growth and decline of green land air purification capacity

V. Current Trends and Policy Simulation

This study investigates appropriate sustainable urban development policy for resolving the conflict between economic development and environmental protection. Current urban development trends without any air purification policy are estimated first. Then public transportation facilitation and green land preservation policies are compared by simulating air pollution in Taipei from 1969 to 2050. The results are demonstrated below:

1.Current development trends of Taipei city, 1969-2050:

(1)Urban development of Taipei cityThe total area of Taipei city is approximately 27,179.97 hectares. From 1969 to 2003, the

developed land area in Taipei city increased by approximately 7,043.32 hectares, and the resident population increased by 1,022,595 persons (see Table 1). That is, the population and developed land in Taipei city almost doubled during that period. Almost 50% of the urban planning land in Taipei city has already been developed. Moreover, approximately 28.2% of the green land in Taipei city (5917.91 hectares, see Table 1) was zoned for construction development during the same period (Taipei City Government, 1970-2004a.

Table 1. Land development in Taipei city from 1969 to 2003. (Unit: person, hectare)

Item Year-End 1969 Year- End 2003

Population 1,604,543.00 2,627,138.00

City planning area 10,783.37 27,179.97

Land for city development 6,362.78 13,406.10

Gree land 20,967.35 15,051.18

Source: This table was arranged by this study. (Taipei City Government, 1970-2004a)

Regarding urban transportation, the number of motor vehicles increases with urban population growth. Table 2 clearly shows that the number of cars in Taipei city increased by 1,586,380 from 1969 to 2003. That is, number of motor vehicle per household increased from 0.29 to 1.85 cars during that period.

Table 2. Number of motor vehicles in Taipei city from 1969 to 2003(Unit: car, %)

Item Year- End 1969 Year- End 2003

Motor vehicles per household 0.29 1.85

Motor vehicle 102,346.00 1,688,726.00

Household 350,821.00 914,716.00

Source: This table was organized by this study. (Taipei City Government, 1970-2004a)

(2)Urban land development and population growthAccording to current trends of urban development in Taipei, the simulation results show

that total area of land development is expected to increase from approximately 7,000 to 8,000 hectares to 2050; see the dotted line in Fig. 4. Meanwhile, the area of green land will decrease from approximately 15,000 to 13,000 hectares. Regarding the population, owing to the negative influences of environmental pollution problems such as air pollution, population stopped increasing with growth in urban land development and remained at around 2.6 million persons from 1990 until recent years; furthermore, the population is expected to decrease to around 2.5 million individuals by 2050; see the dotted line in Fig. 5.





Urban Building Land10,000

7,000

4,000

2

22

2 2 2 2 2 2

1

11

1

1969 1987 2005 2023 2041Time (Year)

Urban Building Land : Before & Current hectare1 1 1Urban Building Land : Current & Future hectare2 2 2

Population4 M

2.5 M

1 M

22

2 2 2 22

22

1

1

1 1

1969 1987 2005 2023 2041Time (Year)

Population : Before & Current person1 1 1 1 1Population : Current & Future person2 2 2 2

Figure 4. Trend of land development in Taipei, 1969-2050

Figure 5. Trend of population growth in Taipei, 1969-2050

(3)Growth in urban vehicle numbers and the air pollution problemPeople who live or work in Taipei city, like residents of other international cities, who have

grown accustomed to using motorized vehicles for transportation. Therefore, massive discharges of polluted air from large active motor vehicles in urban areas have steadily increased air pollution in Taipei. The number of active motor vehicles in Taipei exceeded four millions in 2003, see Fig. 6. From the simulation results, the number of active motor vehicles in Taipei will reach around six million by 2050. Furthermore, the simulated pollutant NOx discharged by motor vehicles in Taipei will increase from 20,000 to 30,000 tons annually in 2050, see Fig. 7. Because of the decrease in green land, the absorption capacity of NOx pollutant also gradually reduced. Consequently, the air pollution problem in Taipei city is worsening. The NOx annual emission amount by active motor vehicles and its parameter data set for SD simulation model, which are according to Taiwan EPA’s data1.

Number of Active Vehicle6 M

3 M

0 2

2

2

22 2

22

2

11

1

1

1969 1978 1987 1996 2005 2014 2023 2032 2041 2050Time (Year)

Number of Active Vehicle : Before & Current car1 1 1Number of Active Vehicle : Current & Future car2 2 2

NOx Emission by Vehicle40,000

20,000

0 2

2

22

22 2 2 2

11

1

1

1969 1987 2005 2023 2041Time (Year)

NOx Emission by Vehicle : Before & Current ton1 1 1NOx Emission by Vehicle : Current & Future ton2 2 2

Figure 6. Trend of active vehicles in Taipei, 1969-2050

Figure 7. Trend of NOx emission by vehicles in Taipei,1969-2050

2.Policy analysis

A dynamic urban system model is designed for simulating and analyzing the complex feedback causality of the air pollution problem. This study attempts to identify appropriate policy for sustainable urban development. Two policies are arranged for assessing their air purification effects: 1) green land preservation; 2) public transportation facilitation. By adding these two policies into the feedback loops of the air purification model mentioned above in Fig. 2, the policy simulation model is shown in Fig. 7, and is used for comparing and evaluating the air purification effects of policies.

Population


+

Number ofVehicle

+

Green Land

-

Air Pollution-

+-

+

Delay

EconomicActivities

PollutantEmission

+

+


+

+


VehiclesOutside City

+

+

+

+Green LandPreserved Public Transport

Facilitated

-

+

-

Figure 8. Feedback loops for simulating air purification policies in Taipei

(1)Green land preservationDue to the area of green land in Taipei has reduced from 77% to 55.38% during 1969-2003

(namely 5917.91 hectares, approximately 28.2% area of green land in Taipei has vanished since 1969), and land development is still continuing (Taipei City Government, 1970-2004a). Green land preservation policy aims to save air purification capability of green land of Taipei. Vegetations in green land are well known to be able to offer fresh air and absorb polluted air; thus green land can purify the air (Beatley, 2000; Hill, 1971; Jensen & Pilegaard, 1993; Sung et al., 1998). That is, the area of green land in a city would determine the capability of that city to purify its polluted air. The amount of leaf area that green land possesses thus is a critical determinant of urban air quality. Particularly, preserving green land prevents excessive urban land development that results in the decrease of urban active population and the associated large volumes of active motor vehicles, which are critical effects of this policy. Consequently, Fig. 7 illustrates that levels of air pollutants in Taipei would reduce so. Parameter data about the volume of NOx absorption by green land and its leaf area set in our SD simulation model of this study, which are according to Taiwan EPA’s data2.





(2)Public transportation facilitationThe level of air pollution in urban area could be decided by active motor vehicle numbers,

travel distance, and emissions of pollutants (Ghose et al., 2004; Marshall et al., 2005). Public transportation facilitation policy is a popular and an effective method of reducing urban air pollution by replacing private transport modes with public modes (Miller & Hoel, 2002). This study finds that by considering the active population in Taipei city that includes outside city workers, annual public transport trips should increase to 2.36 times of the current trip volume (in 2004), thus increasing from 1.5 billion trips to 2.34 billion trips by 2050 (namely increases 0.84 billion trips) (Taipei City Government, 1970-2004a, 2004b); these results of active motor vehicle that one household possesses can be decreased from around 1.95 to 1.62 cars, and annual travel distance of one active motor can be decreased from around 16,440 to 12,500 kilometers (Hsu, 2000; Tsai et al., 2000) in Taipei city.(3)Results

Fig. 9 and Table 3 show the simulation results comparing the implementation of two air purification policies with the continuation of current trends in Taipei city by considering active population numbers, preserved green land area, active motor vehicle numbers, and emissions of NOx pollutants. Besides, simulation values of the amount of NOx remnant of Taipei are shown on Fig. 9 and Tab. 3, which are contributed by the NOx annual emissions amount by active motor vehicles (see Note 1) and by immobile pollutants of Taipei city. The latter NOx emissions are calculated from the NOx emission amount of Taiwan, ratio of north Taiwan air area, and ratio of immobile pollutants of Taipei city measured by Taiwan EPA (TEPA, 2000). The simulation results of policy scenarios presented in this study show that public transportation facilitation focused strategies for air purification are only more effective than green land preservations strategies in the short term. However, in the long term, green land preservation is superior to public transportation facilitation oriented strategies as a means of reducing air pollution.

Owing to public transportation facilitation policy not involving strict controls on land development, the convenient transportation and increasing supply of urban developable land make the city to become more attractive. Therefore, the required land investment increases and enables the number of employees living outside Taipei city to increase by around 0.33 million persons by 2050, see Table 3. Meanwhile, due to poor environment conditions within Taipei, for example air pollution, people prefer live outside Taipei city. Consequently, Taipei’s population only increases by 0.133 million persons by 2050 in the public transportation facilitation oriented scenario. Moreover, comparing to 12,922 hectares green land area remnant on current trend, the area of green land reduces by 118 hectares, and NOx pollutants reduce by only 2,587 tons by 2050 in this scenario. However, total capital expenditure for the public transportation facilitation

policy was 685 N.T. billion dollars higher than projected based on the current trend during the period 1969-2050, see Table 3. Figures 9-13 show the simulation results in detail.

NOx Remnant in The Air60,000

45,000

30,000

15,000

0

3

33

3

33 3

33 3 3

3

22

2

2

22 2 2

2 22 2

11

11

11

1 1 1 1 1 11

1969 1978 1987 1996 2005 2014 2023 2032 2041 2050Time (Year)

NOx Remnant in The Air : Scenario 1 Preserve Green Land ton1 1 1

NOx Remnant in The Air : Scenario 2 Facilitate Public Transit ton2 2 2

NOx Remnant in The Air : Current ton3 3 3 3 3 3 3

Figure 9. Trend of NOx remnant in the air in Taipei, three scenarios, 1969-2050

Table 3. Simulation Results of Policy Scenarios in 2050’s Taipei city. (Unit: hectare, ton, Million persons, and N.T. Billion dollars /ton).

POLICY SCENARIOS(2004- 2050)

Current Trend

1 2

Green land preservation

Public transportation facilitation

Population 2.628 M 3.174 M 2.741 M

Population increased － 0.546 M 0.113 M

Employees not live in city 0.696 M 0.412 M 1.026 M

Increased employees not live in city

－ -0.284 M 0.330 M

Active motor vehicles 5.207 M 3.131 M 6.016 M

Increased active motor vehicle － -2.076 M 0.809 M

Green land 12,922 ha 13,476a ha 12,804 ha

Green land preserved － 554 ha -118 ha

NOx pollutant remnant 46,380 ton 35,581 ton 43,793 ton

NOx emission total decreased － 10,799 ton 2,587 ton

Total capital expenditure － 0b 685c B





Source: This table was drawn up by this study and the data originated from Year 1970-2004 statistical abstract of Taipei Municipality. (Taipei City Government, 2004.

aSince green land area in Taipei has reduced from 77% to 55.38% during 1969-2003, green land preservation policy takes 52-55% green land area in Taipei as a basis to value air quality and decide whether permit of developing green land or not from 2004. When percentage of green land area is lower than 52% and at the condition of level of air pollution is not better, land development is not allowed anymore. Therefore, during 2004-2050, preserved green land area of Taipei is expected to increase to around 554 hectares and will rise to 13,476 hectare by green land preservation policy by 2050.

bThe green land preservation policy does not increase the capital expenditure of Taipei city, because the green land is preserved by land development quota for controlling urban populations and the size of their economic activities by placing quotas on developable land, in order to preserve urban green land.

cAccording to annual construction budget of Rapid Transit (MRT and MCT) system planned by Department of Budget, Accounting and Statistics of Taipei City Government, and numbers of annual public transport trips of Taipei (Taipei City Government, 1970-2004a, 2004b). For increasing annual public transport trips from 1.5 billion trips to 2.34 billion trips (namely increases 0.84 billion trips), at the expense of increasing one passenger (about 816.52 N.T. dollars), total capital expenditure for the public transportation facilitation policy was 685 N.T. billion dollars by 2050.

Number of Active Vehicle8 M

4 M

0 3

3

33

33 3 3 3

2

22

22 2

2 2 2

11

1

11 1 1

1 1

1969 1978 1987 1996 2005 2014 2023 2032 2041 2050Time (Year)

Number of Active Vehicle : Scenario 1 Preserve Green Land car1 1Number of Active Vehicle : Scenario 2 Facilitate Public Transit car2 2Number of Active Vehicle : Current car3 3 3 3 3

NOx Emission by Vehicle40,000

20,000

0 3

3

33 3

3 3 3

2

2

22

2 2 22 2

11

1

11 1 1 1

1

1969 1987 2005 2023 2041Time (Year)

NOx Emission by Vehicle : Scenario 1 Preserve Green Land ton1 1NOx Emission by Vehicle : Scenario 2 Facilitate Public Transit ton2 2NOx Emission by Vehicle : Current ton3 3 3 3 3

Figure 10. Trend of active vehicles num-bers in Taipei, three scenarios, 1969-2050

Figure 11. Trend of NOx emissions by ve-hicles in Taipei, three scenarios, 1969-2050

Population4 M

2.5 M

1 M

33

3 3 3 3 33

3

22

2 2 2 2 2 2 2

1

1

1 1 1 11 1 1

1969 1987 2005 2023 2041Time (Year)

Population : Scenario 1 Preserve Green Land person1 1 1 1Population : Scenario 2 Facilitate Public Transit person2 2 2Population : Current person3 3 3 3 3 3

Employees not Live in City2 M

1 M

03

33

3 3 3 3 33

2

2 22 2 2

2 22

1

11

1 11 1

11

1969 1978 1987 1996 2005 2014 2023 2032 2041 2050Time (Year)

Employees not Live in City : Scenario 1 Preserve Green Land person1 1Employees not Live in City : Scenario 2 Facilitate Public Transit person2Employees not Live in City : Current person3 3 3 3

Figure 12. Trend of Population growth in Tai-pei, three scenarios, 1969-2050

Figure 13. Trend of Taipei workers not living in the city of Taipei, three scenari-os, 1969-2050

On the other hand, the air purification effect of green land preservation policy was insignificant at the start of the first decade. However, comparing to 12,922 hectares green land area remnant by current trend, preserved green land area of Taipei by green land preservation policy will rise to 13,476 hectare by 2050 (namely increase green land area 554 hectares), see Tab. 3., the cumulative effect of air purification will be significant in the long term. Although this policy may reduce the required land investment and results in fewer employment opportunities, and thus reduces the numbers of workers commuting to Taipei city from elsewhere; the better air quality and environment conditions will enable Taipei city to attract more immigrants. Consequently, the population of Taipei thus is expected to increase to around 0.546 million persons, and the population working in Taipei but living outside the city will decrease to around 0.284 million persons. That is, the green land preservation policy will lead to a more compact city. Moreover, the area of preserved green land is expected to increase to around 554 hectares and air pollutant NOx is expected to reduce by 10,799 tons in 2050. The most important advantage of the green land preservation policy is that it does not increase the capital expenditure of Taipei city, because the green land is donated by land development quota for controlling urban populations and the size of urban economic activities by placing quotas on developable land from 2004 to 2050, and thus preserve urban green land. Figure 9-13 shows the detailed simulation results. Consequently, the green land preservation policy is superior to the public transportation





facilitation policy from the perspectives of sustainable urban development and fiscal efficiency.

VI. Conclusions

Sustainable urban development requires continuous and long-term efforts towards achieving a balance of environmental, social and economic development. Although development to extremes frequently leads to a reversal of the development trend, the natural environment generally does not reveal its limits of exhaustible tolerance until it is too late. Since the intrinsic nature of mutual conflicts among sectoral or departmental development always exists in the path towards urban sustainability, market mechanisms cannot be relied upon to attain urban sustainability. Seeking better urban sustainability policies becomes a key duty of government. Policy quality is assessed based on its forecasting capabilities and the feasibility of implementation. This work takes air purification in Taipei city as a case study for investigating the policy issue. The findings of this study are described as follows:

1.Sustainable development analysis needs a comprehensive approach

Environmental development is highly complex, and involves a system of interwoven components with numerous positive and negative feedback loops. Ignoring the interactive relationship among sectors or departments generally leads to the establishment of other new problems that require solving. A comprehensive macro approach is superior to an individual micro approach for dealing with complex environmental problems and intrinsically understanding sustainable urban development. The system dynamic approach can logically track the feedback loops among sectors in urban development, therefore the combined effects can be recognized in a complex system. The thinking logic of system dynamics provides a comprehensive analytical approach, and this technique leads to a more realistic forecasting result, which is useful in policy evaluation.

2.Green land preservation is increasingly important in Taipei city

In an atmosphere of global competition, people generally consider that land development can bring increased benefits to a city or its residents. The simulation results presented in this study demonstrate that current land development trends merely bring short-term benefits, but do not effectively achieve long-term benefits from the perspective of sustainable development. This

result initially appears surprising, but stands up to careful investigation. The primary reason for this phenomenon is that land development can increase population and economic activity, but reduces the green land areas consequently damages air purification capabilities and human health thus causing irreparable damage.

3. Long-term and comprehensive effects of green land preservation can be superior to those of facilitating public transportation for air purification in Taipei city

This study assessing the long-term and comprehensive effects of air purification policies in Taipei city found that, though facilitating public transportation can directly reduce the number of private vehicles, thus reducing air pollutant emissions, the indirect effects of increasing numbers of employees and population moving out to suburban area of public transportation facilitation policy should not be underestimated and ignored. The large increase in the number of active private vehicles associated with increasing numbers of Taipei commuters living outside the city can increase air pollution levels. Once the indirect effect of increasing numbers of employees and population moving out to suburban area surpasses the direct effect of the public transportation facilitation policy, urban development becomes increasingly sprawling, and air pollutant emissions increase. The simulation results presented in this investigation demonstrate that the long-term and comprehensive effects of green land preservation on air purification can exceed the effects of public transportation facilitation from the sustainable urban development and fiscal efficiency perspectives in Taipei city.

Acknowledgement

The authors gratefully acknowledge the anonymous reviewers for their thoughtful comments and very helpful suggestions in the revision of this paper. This study is supported by grants from Taiwan National Science Council of Republic of China (NSC92-2415-H006-006).

Notes

1.The emission modules of vehicles are different from conditions of gasoline, engine, speed, type, and age. Besides, the uncertain conditions of vehicles from outside city that result in the work to compute the exact emission amount by various vehicles become more difficult. Therefore, this study tries to use three simplified variables to simulate annual NOx emissions by vehicles, which are “Number of Active Vehicle”, “NOx Emission Modulus on Vehicle”,





and “Distance Traveled by Vehicle” in our SD simulation model. More, the data source of the annual NOx emissions by vehicles in this study comes from the Taiwan EPA’s publication data. After checks another calculation of the annual mobile NOx emissions of Taipei city from the Taiwan EPA’s publication data (Institute of Transportation, Ministry of Transportation and Communications,, Taiwan, R.O.C. (MOTC), 2006; TEPA, 2000), the experimental modulus value per kilometer of NOx emissions discharged by a vehicle is set as 0.3g/km and the average distance per year of a vehicle is set as 16440.3km/year in our SD simulation model of this study (TEPA, 1998, 2000). The equations for calculation of NOx emissions amount by active motor vehicles are listed below (Tsai et al., 2000):

E = M × V* × 10-3, (1)EF = E / L, (2)where E is the exhaust amount of the pollutant (g) in a specific driving mode, M is the

concentration of the pollutant (mg N/m3), V* is the normalized value of the exhaust gas volume given by the dynamometer laboratory of the motorcycle manufacture plant after temperature and pressure correction (N m3), L is the traveled mileage during the test procedure (km), and finally EF is the emission factor of that pollutant (g/km). Therefore, this study uses the equations to simulate annual NOx emissions amount by active motor vehicles in Taipei.

2.We have designed variables of “NOx absorption by green land” and “the leaf area of green land” per hectare in our SD simulation model to simulate the capacity of air purification effects of green land. Parameter data about the volume of “NOx absorption by green land” set in our SD simulation model is 0.105477 ton/ha, it is according to average experimental modulus value from EPTA and other related research data of various green vegetation, which were measured repeatedly in laboratories that imitated conditions like in real world (Dwyer et al., 1991;Hsieh and Sun, 2001 Jensen, 1993;Sung et al, 1998; TEPA, 1997. According to the related research data (Kao and Cheng, 1997; TEPA, 1997), we calculate the leaf area range of green land is about 3.5-21.5 ha. Therefore, this study concerns green land in urban area have different conditions on aspects of various vegetation that include tree, shrub, ground cover plant etc., vegetation density, and vegetation community form, the parameter data about “the leaf area of green land” set in our SD simulation model is 12 ha.

References

Ackoff, R.L. and Pourdehnad J. (2001) On Misdirected Systems. Systems Research and Behavioral Science. 18: 199-205.

Beatley, T. (2000) Green urbanism: learning from European cities, Island Press.

Campbell, S. (1996) Green Cities, Growing Cities, Just Cities? Urban Planning and the Contradictions of Sustainable Development. Journal of American Planning Association, 62 (3): 296-312.

Camagni, R., Capello, R., and Niukamp, P. (2001) Managing Sustainable Urban Environments, in Ronan Paddison (Ed.), Handbook of Urban Studies, London: Sage Publications, pp.124-139.

Coyle, R.G. (1996). System Dynamics Modeling: A Practical Approach, Chapman & Hall, New York.

Davidson, E. A. (2001) You Can’t Eat Gnp: Economics As If Ecology Mattered, The Perseus Books Group Perseus Publishing.

Dwyer, J. F., Schroeder, H. W., and Gobster, P. H. (1991) The Significance of Urban Trees and Forests: Toward a Deeper Understanding of Values. Journal of Arboriculture, 17 (10) October: 276-284.

Environmental Protection Agency, (2004) Air Pollution, http://www.epa.gov /airnow /aqibroch /aqi.html

Ghose, M.K., Paul, R., and Banerjee, S.K. (2004) Assessment of the impacts of vehicular emissions on urban air quality and its management in Indian context: the case of Kolkata (Calcutta). Environmental Science & Policy, 7: 345-351.

Hawken, P. , Amory, L. , and Hunter, L. L. (2000) Natural Capitalism: The Next Industrial Revolution, James & James Ltd Earthscan.

Hill, A. C. (1971) Vegetation: A Sink for Atmospheric Pollutants. Journal of the Air Pollution control Association, 21 (6): 341-346.

Hsieh, W. W. and Sun, E. J. (2001) Determination of Uptake Rates of Sulfur Dioxide, Nitrogen and Ozone by Ten Plant Species or Varieties in Wind Tunnel. Journal of the Environmental Protection Society of the Republic of China, 24 (2): 142-155.





Hsu, Y.C. (2000) The Relationship between Volatile Organic Profiles and Emission Sources in Ozone Episode Region(in Chinese). Dissertation for Doctor of Philosophy Department of Environmental Engineering National Cheng Kung University, Taiwan, R.O.C.

Institute of Transportation, Ministry of Transportation and Communications, Taiwan, R.O.C. (MOTC) (2006) Growth Trend of Transportation and Communications in Taiwan Area: Motor Vehicles Statistics in Taiwan Area, http://www.iot.gov.tw/public/Attachment/591415325871.xls.

Jan, T.S. & Jan, C.G. (2000) Designing Simulation Software to Facilitate Learning of Quantities System Dynamics Skill: A Case Study in Taiwan. Journal of the Operational Research Society, 51: 1409-1419.

Jan, C. G. , (2003) Policies for developing defense technology in newly industrialized countries: a case study of Taiwan. Technology in Society, 25 (3): 351-368.

Jensen, E.S. (1993) The Faculty of Air Cleaning on Green Vegetables (in Chinese). Scientific Agriculture, 41(7,8): 163-176.

Jensen, E.S. & Pilegaard, K. (1993) Absorption of nitrogen dioxide by barley in open-top chamber. The New Phytologist, 123:359-364.

Kao, C. and Cheng, J. F. (1997) A Study on the Leaf Area of Ficus religiosa L. in Urban Areas (in Chinese). Quarterly Journal of the Experimental Forest of National Taiwan University, 11(4): 11-19.

Liu, R.X. ; Gao, X.Y. ; Yang, D.S. ; Xu, X.G. (2005) Control of diesel soot and NOx emissions with a particulate trap and EGR. Journal of Environmental Sciences, 17 (2): 245-248.

Marshall, J.D., McKone, T.E., Deakin, E. & Nazaroff, W.W (2005) Inhalation of Motor Vehicle Emissions: Effects of Urban Population and Land Area. Atmospheric Environment, 39: 283-295.

Martell, Luke, (1994) Ecology and Society, Amherst: University of Massachusetts Press, 1994.

Miller, Jr. G. T. (2004) Living in the environment: principles, connections, and solutions, Brooks/Cole, 13eds.

Miller, J.S. & Hoel, L.A. (2002) The “Smart Growth” Debate: Best Practices for Urban Transportation Planning. Socio-Economic Planning Sciences, 36: 1-24.

Occupational and Environmental Health Protection of the Human Environment World Health Organization, (2001) WHO Strategy on Air Quality and Health, Revised final draft, Geneva.

Pargal, S. , and Heil, M. , (2000) Reducing Air Pollution from Urban Passenger Transport: A Framework for Policy Analysis. Journal of Environmental Planning and Management, 43 (5): 665-688.

Roberts, E.B.(ed). (1978) Managerial Applications of System Dynamics: An Introduction, Waltham, MA: Pegasus Communications, pp.3-35.

Russell, A.; Milford, J.; Bergin, M. S.; McBride, S.; McNair, L.; Yang, Y.; Stockwell, W. R.; Croes, B. (1995) Urban Ozone Control and Atmospheric Reactivity of Organic Gases. Science, New Series, 269 (5223): 491-495.

Stearns, F. and M. , T. (1974) The Urban Ecosystem: A Holistic Approach, Dowden, Hutchinson & Ross, Inc.

Sterman, J. D. (2000) Business dynamics: systems thinking and modeling for a complex world, Boston: Irwin McGraw-Hill.

Sung, C. H. , Wang, Y. N. , Sun, E. J. , and Ho, L. H. (1998) Evaluation of Tree Species for Absorption and Tolerance to Ozone and Nitrogen Dioxide (III)(in Chinese). Quarterly Journal of the Experimental Forest of National Taiwan University, 12(4): 269-288.

Taipei City Government, (1970-2004a) The Statistical Abstract of Taipei City, Department of Budget, Accounting and Statistics Taipei City Government Republic of China.

Taipei City Government, 2004b, http://www.dbas.taipei.gov.tw/stat/abstract/index.htm.

TEPA (1997) The Air Purification Capacity Estimation of Environmental Preservation Park (in Chinese), Grant No. EPA-86-FA52-09-71. Environmental Protection Administration, Taiwan, Republic of China.

TEPA (1998) Air pollutants Quota Control of Kaohsiung and Ping-Tung Area in Southern Taiwan, B1 Plan: Actinism Characteristics Analysis of VOCs Emission by Mobile Pollutants. (in Chinese), Grant No. EPA-87-FA42-03-F5-B1. Environmental Protection Administration, Taiwan, Republic of China.

TEPA (2000) Record of Actual Events of Taiwan’s Air Quality Protection for 25 Years (1975-2000) (in Chinese). Environmental Protection Administration, Taiwan, Republic of China.



Tsai, J. H. ; Hsu, Y. C. ; Weng, H. C. ; Lin, W. Y. , and Jeng, F. T. (2000) Air pollutant emission factors from new and in-use motorcycles. ATMOSPHERIC ENVIRONMENT, 34: 4747-4754.

Wang, Q. D. ; He, K. B. ; Huo, H. ; Lents, J. (2005) Real-world vehicle emission factors in Chinese Metropolis City – Beijing. Journal of Environmental Sciences, 17 (2): 319-326.

Wheeler, S. (1996) Sustainable Urban Development: A Literature Review and Analysis, University of California at Berkeley Press, California.

Zhang, R. ; Tie, X. , and Bond, D. W. (2003) Impacts of Anthropogenic and Natural NOx Sources over the U.S. on Tropospheric Chemistry. Proceedings of the National Academy of Sciences of the United States of America, 100 (4): 1505-1509.

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