Outdoor activities have been recently restricted because of the occurrence of particulate matter. Moreover, people have increased concerns on health effects due to the growth of particulate matter. After identifying particulate matter as a disaster, the city of Seoul is taking measures to limit the operation of vehicles and their pollution during the issuance of emergency reduction actions. This done with the aim of ensuring that emissions and exposure are reduced. However, besides preventive measures, various measures should be put in place to reduce particulate matter that has been already generated. In this respect, the importance of green infrastructures, such as parks, green spaces and trees in urban areas is increasing as one of the ways to reduce particulate matter. In order to understand the reduction effects of particulate matter on trees in the city, the particulate matter adsorption of the trees was analyzed through field measurements that targeted the street trees in the major roadsides of Seoul. Expansion plans for green infrastructure, such as theselection of appropriate species to reduce particulate matter and methods of arranging the trees were proposed. The main contents were categorized into analysis of trends related to green infrastructure, review of domestic and foreign green infrastructures related to air pollution, analysis on particulate matter reduction effect on green infrastructure, and proposition on green infrastructure expansion plans for coping with particulate matter.

In the analysis of trends related to green infrastructures, the green and street trees were selected as green infrastructure for reducing the particulate matter. The green infrastructure of Seoul was analyzed. In addition, previous studies on green infrastructure for particulate matter reduction were reviewed.

Second, the domestic and foreign green infrastructure cases related to air pollution were reviewed. The cases for green infrastructure policy related to overseas air pollution were also reviewed. As a result of examining the instances of green infrastructures for particulate matter reduction, a review was done on the city forest(taking into consideration the wind path of Stuttgart in Germany), green wall of Europe and domestic cases, such as the composition of urban forests for reduction of particulate matter, greening business, and the particulate matter reduction bench.

Third, the effect of particulate matter reduction on green infrastructure was analyzed. Through the analysis of the current status of tree species in Seoul, the Ginkgo biloba L., Platanus occidentalis L., Zelkova serrata (Thunb.)Makino, Prunus yedoensis Matsum, and Pinus densiflora Siebold & Zucc. in Seoul Forest and Yangjae Citizen’s Forest were selected. From the analysis of particulate matter adsorption in major species, the species that most effectively adsorbs particulate matter per unit area was the Zelkova serrata (Thunb.)Makino and Platanus occidentalis L. The amount of particulate matter adsorption by leaf area index(LAI) was 1.4~2.5g/㎡ for the Zelkova serrata (Thunb.)Makino, 0.8g/㎡ for Platanus occidentalis L., 0.4~0.9g/㎡ for Pinus densiflora Siebold & Zucc., 0.5~0.7g/㎡ for Prunus yedoensis Matsum, and 0.2~0.4g/㎡ for Ginkgo biloba L. The amount of particulate matter adsorption per tree within the range of DBH for the target trees was 66.6g average for Zelkova serrata (Thunb.)Makino, showing that it had a relatively more particulate matter adsorption effect(37~96g/tree). The air pollution tolerance index per tree within the Seoul Forest and Yangjae Citizen’s Forest did not show any statistically significant difference. However, the air pollution resistance index for the Platanus occidentalis L., Pinus densiflora Siebold & Zucc., and Prunus yedoensis Matsum. were relatively higher. However, all the five species did show similar figures.

Depending on the location and pruning of the target trees, the amount of adsorption varied. The number of analysis on particulate matter adsorption was insignificant and focused only towards a certain season. As a result, the estimated amount of particulate matter per tree may have some deviation. In the future, all seasonal repeat measurements are required for more accurate results. Moreover, a complex review of various variables is required. In addition, a planting method should also be developed.

From the study of analyzing the distribution of particulate matter and green infrastructure in Seoul, the results showed that the large green areas had a relatively low concentration compared to other areas. To propose a green infrastructure expansion deployment plan, a green infrastructure connectivity was analyzed, targeting built-up areas having relatively high particulate matter and Yeongdeungpo-gu and Dongdaemun-gu with low green areas. Based on previous researches, a proposal was made by applying green infrastructure elements for reducing particulate matter.

Finally, a green infrastructure expansion plan for coping with particulate matter was proposed. Based on urban characteristics and given the limited green space area of Seoul, in order to reduce particulate matter during urban greening, it is necessary to utilize plant species that have relatively high adsorption ability against the particulate matter. Since the trees that had a high total leaf area or area index while having a high per unit adsorption area had higher adsorption amount of particulate matter, the Zelkova serrata (Thunb.)Makino is relatively the most efficient. However, since deciduous forest trees do not have leaves in autumn and winter, the adsorption effects of the particulate matter can be reduced, whereas the pine and evergreen needle-leaf trees can be said to be relatively effective for particulate matter reduction during winter and early spring. Therefore, by planting the evergreen trees together, the seasonal characteristics of particulate matter reduction should be complemented. The key to green infrastructure deployment for the reduction of particulate matter is the fact that trees and greenery play a role of blocking and filtering particulate matter, and multi-layered planting is important. During multi-layer planting the method of arbor + arborescent + shrub + herb is the same. However, in the case of a residential area requiring protection from particulate matter vertically from the source, a dense and stepped arrangement is effective. Meanwhile, for the areas where smooth dust emission is required, a composite arrangement is effective such that polluted air is discharged to the outside of the city through a constant gap between the trees. However, since in Seoul there is no room for green space due to the city’s characteristics, it is desirable to consider stereoscopic greening, such as wall greening and rooftop greening. Moreover, in order to efficiently expand the green infrastructure, we proposed ways to build a green infrastructure system through citizen participation.