녹지의 대기환경영향에 관한 연구

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(1)Impacts of Green Spaces on Air Quality. Hyun Soo Joo Seogcheol Kim.

(2) Research Staff. Leading Researcher: Hyun Soo Joo (Korea Environment Institute) Participating Researcher: Seogcheol Kim (Boolt Simulation Technology). C 2005 by Korea Environment Institute Copyright ○. All rights reserved. No part of this publication may be reproduced or transmitted in any form or any means without permission in writing from the publisher. Publisher: Suh Sung Yoon Published by: Korea Environment Institute 613-2 Bulgwang-Dong, Eunpyeong-Gu, Seoul, 122-706, Republic of Korea Tel.(822) 380-7777 Fax.(822) 380-7799 http://www.kei.re.kr Published and printed in Dec. 2005 ISBN 89-8464-178-2 93530.

(3) Foreword The Kyoto Protocol and the Marrakesh Accords to the Framework Convention on Climate Change recognize Land Use, Land-Use Change, and Forest (LULUCF) activities - mainly afforestation and reforestation - as a potential means to reduce greenhouse gases in the atmosphere. And thus, as a measure to meet emission reduction targets allocated to developed countries. In recent years, LULUCF activity, commonly referred to as carbon sink management, has received a great deal of attention internationally, and many researches have been participating in this area. Despite the increasing attention to carbon-sink management under the climate change negotiation and research arena, very little consideration is given to carbon-sink management in Korea except for the construction of necessary statistics on greenhouse gas emissions and removals by LULUCF activities in the National Communication under the Convention. The purpose of this study is to evaluate the feasibility of utilizing an econometric land use model to estimate the costs of carbon-sink programs in Korea. In literature, most of the economic studies of carbon-sink management evaluate governmental policy, which is designed to encourage the conversion of agricultural and/or marginal land to forests. A similar approach will be employed in this study. I hope that this study will be an important first step toward the facilitation of related research. I would like to thank the authors, SoEun Ahn and KiJoo Han, for their hard work. I also wish to express my sincere thanks to the reviewers for their helpful comments and suggestions on this study.. Suh Sung Yoon President Korea Environment Institute.

(4) Contents. Foreword Chapter 1. Introduction ·························································1 Chapter 2. Impacts of Green on Air Quality in Urban Area········· 3 1. Prediction Model for the air quality in urban treed area ··················· 3 2. Impacts of Urban Neighborhood Park Trees on Air Quality ············· 4 3. Impacts of Street Canyon Trees on Air Quality ································ 5. Chapter 3. Conclusion ························································ 9.

(5) Chapter 1 Introduction 1. Chapter 1. Introduction Trees absorb and purify air pollutants through processes such as metabolism and photosynthesis, emitting beneficial substances for the human body through their pores. They not only influence the urban micro meteorology by cooling down and dispersing air pollutants but also protect the Earth from the various erosions. Also, the green color of the trees provides people with aesthetic effects and psychological tranquility. As you can see, trees do a lot of good for humankind. Recently, green spaces (treed area) in air-contaminated urban areas have come into notice as possible means to curtail air pollution. In order to estimate quantitatively the impacts of green spaces on our air quality, one must consider not only a tree's function of purifying air pollutants but also its micro meteorology such as wind flow conditions. However, it was discovered that previous studies have considered only the purification of air pollutants by trees, neglecting the behavior of air pollutants when influenced by the wind in an actual system. Consequently, the real impacts of green spaces on air quality have not been established accurately. The objective of this study was to find the quantitative relation between urban treed areas and atmosphere environment in real conditions, considering both of the aspects described above. Especially,「the gasphase air pollutants(SOx and NOx) decreasing function of trees in urban area」was explored. In other words, this study chose urban sites, because this area has been a major concern with regards to the air pollution matter. The study focuses on the air pollutants, sulfur oxide and nitrogen oxide, both of which are gas-phase pollutants. Further studies, based on this year, may be done for more extensive areas and diversified air pollutants like ozone, etc. This study classifies urban treed areas as neighborhood parks treed areas and street canyon trees. It also develops a quantitative analysis method for evaluating the relationship between the atmosphere and its gas phase air pollutants (sulfur oxides and nitrogen oxides). The neighborhood park is a typical urban park. Thus, information such as the size of a treed area that could influence the atmosphere environment in actual settings is necessary. A street canyon is an area,.

(6) 2. Impacts of Green Spaces on Air Quality. formed in a street between two rows of buildings. It is a geographically handicapped area with a great potential of danger under local atmospheric pollution, so its atmospheric environment is a much more important issue. Through the above mentioned modeling methods, evaluation system of air quality influence in treed area have been adopted in a number of cases to analyze the air pollution decreasing function of trees in different types of urban treed areas. From this, the best environment for encouraging the atmosphere improving function of urban treed areas was investigated. The results will be used as a basis for planning treed areas to improve the urban air quality. ..

(7) Chapter 2. Impacts of Green Spaces on Air Quality in Urban Area 3. Chapter 2. Impacts of Green Spaces on Air Quality in Urban Area 1. Prediction Model for the air quality in Urban treed areas There are many approaches to analyze the phenomena of air pollutants dispersion in urban areas. It is classified into three categories using 1) actual measurement, 2) characteristics of overall building structure, and 3) Computational fluid dynamics (CFD). In this study, the CFD methodology was adopted. CFD, which has recently been used in more and more fields, is able to reflect individual building structures into the analysis of air pollutants dispersion instead of ambiguously producing parameters such as overall building structure. In order to analyze air pollutant dispersion in urban treed area, a basic model to reflect the specific details of the area is required. On this point, CFD has an advantage when compared with other methods. The Finite Difference Method (FDM) was applied to fluid flow and concentration equations for the numerical analysis of CFD. Second order FDM and third order Runge-Kutta were also applied to the space and time of the model, respectively. The virtual boundary method and Large Eddy Simulation (LES) model were used to reflect complicated topography with high altitude differences and turbulence components using sizes smaller than model dimensions..

(8) 4. Impacts of Green Spaces on Air Quality. It is known that modeling errors range within an accuracy zone of 20% when applied to the 2nd order LES model. The accuracy model developed in this study is expected to be the same as that of a general 2nd order LES model though it may be unreasonable to estimate the accuracy of the numerical method by the magnitude order of FDM. According to literature reviews of the previous studies on LES, VBM CFD model's basic algorithm, the model can simulate the system with very complicated topography properly. 2. Impacts of Urban Neighborhood Park Trees on Air Quality We set up the Pagoda Park and its neighborhood in Seoul as a modeling area to analyze air quality is influenced by urban neighborhood park trees. The size of the whole modeling area is 882m (East-West) x 554m (North-South. Disposition of buildings and roads in a modeling area were projected in the model as they are). First, we applied two values (0.02m/sec and 0.08m/sec) of the tree's deposition velocity to gaseous non-reacting air pollutants in order to estimate what ranges of deposition velocity can affect air quality in the Pagoda-sized Park, assuming that the velocity is constant. According to the modeling results of the average concentrations at 10 m in height, Vd=0.08m/sec improves air quality very well but it is impossible to observe such a number in the real world. As deposition velocity decreases to 0.02m/sec, the highest value found in previous studies of measurement or estimation for a tree's deposition velocity, the air quality improving effect becomes almost negligible..

(9) Chapter 2. Impacts of Green Spaces on Air Quality in Urban Area 5. Therefore, it is concluded that a tree's function of purifying (absorbing) air pollutants is not as important as the dispersion by wind, with regards to air quality improvement in the Pagoda-sized treed area. This conclusion was deduced from the modeling results for gaseous nonreacting air pollutants and does not necessarily apply to all types of air pollutants. When an urban neighborhood park develops buildings, roads, etc., air quality in related areas may worsen. The tree's capacity for purifying pollutants decreases and emission sources are added. In this study, we assumed that Pagoda Park was developed into buildings and roads just like the above situation and simulated the change in air quality. According to the modeling results of the average concentrations at 10 m in height, air quality worsens almost twice as much compared with to an undeveloped site. From the results of the two case studies above, it is concluded that urban neighborhood parks have an important role in suppressing the construction of emission sources which drive urban air quality to decrease, even though the park's trees have a small air purifying function. Especially in urban areas fully contaminated by air pollutants, the first air quality management policy that one must consider is the conservation of green spaces in neighborhood parks. 3. Impacts of Street Canyon Trees on Air Quality In this study, street canyon trees as well as park trees were the main subjects to analysis studying the air quality effect. A crown of trees in street canyons consisting of relatively short buildings and is placed.

(10) 6. Impacts of Green Spaces on Air Quality. upwind, wind flowing at right angles with the street canyon improves air quality very well. Wind flowing at right angles with street canyon is a most handicapped situation regarding contamination because of air pollutants accumulation. According to the modeling results of street canyons with trees, air pollutants' concentration decreases dramatically especially in side walk areas upwind. A degree of decrease is also expected in vehicle range areas. As for the side walk areas downwind, its tendencies are not clear as the concentration change varies with the height and the overall concentrations with or without trees remain relatively the same. Such an effect cannot be expected in deep street canyon structure which consists of about 60m tall buildings. The air quality improving effect is shortened in cases where the height of the trees is much higher than the street canyon's buildings. Modeling results of 10m tall street canyons with 12m tall trees and 1m/sec wind flow at right angles with the canyon showed a 85% decrease of pollutant concentrations within 8-27 minutes. This effect is caused by air flow changes from the crown of trees which enhances the exchange between fresh (the outside of canyon) and contaminated (the inside of canyon) air, not from the trees' air purifying (absorbing) function. A similar effect can be expected in the case of asymmetric structured street canyons where the height of both sides of the building is different, even without trees. In this instant, planting trees which arey higher than.

(11) Chapter 2. Impacts of Green Spaces on Air Quality in Urban Area 7. buildings. placed. upwind. accelerate. the. effect of. air. quality. improvement. The most important parameter influencing the air quality improvement effect is the height of trees relative to the height of buildings; in addition, the shape and porosity of the crown of trees are important parameters. The width of sidewalks, position of trees, deposition velocity, etc do not affect air quality..

(12) 8. Impacts of Green Spaces on Air Quality.

(13) Chapter 3. Conclusion 9. Chapter 3. Conclusion The objective of the study was to find out the quantitative relationship between urban treed areas and the atmosphere environment in real conditions, focusing on the tree’s function of decreasing gas-phase, nonreacting air pollutant (SOx and NOx) in urban areas. This study classified urban treed area into neighborhood parks treed area and street canyon trees. It also developed a quantitative analysis method for evaluating the influence of the atmosphere in two types of treed areas. Korean and other general guidelines for the management of trees in severely contaminated urban areas suggest planting trees which have the ability of absorbing air pollutants through metabolism. However, according to modeling results, the most important parameters to improving air quality are the height of trees relative to the street canyon's building rather than the capacity of absorbing air pollutants. The results will be used as a basis for planning treed areas to improve urban air quality..

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