A Study on the Spatial Distribution of Air Pollutants in Seoul Metropolitan City Park, Junseo David

1. Introduction

Globally, aimless and careless urbanization and urban sprawl have caused an increase in automobiles and industrial facilities, resulting in various urban environmental problems [1]. Among them, air pollution is threatening the health of urban residents worldwide due to various reasons such as an increase in factory facilities, automobile use, and fossil fuels [2]. In particular, exposure to air pollution has negative effects on mortality, cardiovascular morbidity, respiratory health, and fertility in women [3-5]. Additionally, exposure to air pollution can impede lung development and promote respiratory diseases in children and adolescents, which can accumulate into adulthood and increase cardiopulmonary mortality and diseases [6]. Accordingly, the WHO and the international community have made efforts to reduce air pollution by setting air quality standards. According to the WHO, about 4.2 million people die each year from diseases related to air pollution and about 91% of the world's population lives in urban areas where air quality levels exceed the WHO standards. [7].

In the case of Korea, rapid economic growth has resulted in a global economic powerhouse in a short period of time. However, this improvement has had negative effects of worsening air pollution in Seoul and its surrounding areas. In the case of Seoul, the concentration of PM10, an air pollutant that has recently received a lot of environmental attention, is steadily increasing. The PM2.5 concentration, which has been designated as a class 1 carcinogen by the WHO, has been on the rise since the start of observation in 2013. The concentrations of nitrogen dioxide (NO2) mainly generated in automobiles, and sulfur dioxide (SO2) mainly emitted from fuel combustion and industrial processes are similar to those of particulate matter. As such, major air pollutants tend to be similar or worse compared to the past, and strategies and policy solutions to reduce air pollution in the city are desperately needed. Therefore, this study aims to examine the spatial distribution and regional differences of various air pollutants including particulate matter, and to analyze the correlation between air pollutants in Seoul Metropolitan City, the capital of Korea.

2. Literature Review

According to the Organization for Economic Co-operation and Development (OECD)’s glossary of statistical terms [8] is defined as “the presence of contaminant or pollutant substances in the air that does not disperse properly and that interfere with human health or welfare, or produce other harmful environmental effects.” In Korea, the Clean Air Conservation Act was first enacted in 1980 to mitigate the issues of air pollution. This Act was enacted to manage and conserve the atmospheric environment in a proper and sustainable manner to provide a healthy and comfortable environment. Air pollutants are found in the air in two major forms: a gaseous form of gases and in a solid form from particulate matters suspended in the air [9]. Gaseous matters are produced at the time of combustion, synthesis, and decomposition of matter. Particulate matters are produced at the time of crushing, sorting, piling, reloading, mechanically treating, combusting, synthesizing, or decomposing matter.

Air pollution is closely related to urban characteristics such as population, land use,

transportation, and industrial activity [10]. Thus, research on air pollution and urban environmental characteristics is continuously being conducted universally. For example, Liu et al. [11] conducted a study to inspect the spatial variation of PM2.5 and NO2 in Shanghai, China. They found that only NO2 concentration was found to be high in the residential areas and the concentration of all pollutants was high in the industrial areas, regardless of the type of air pollutant. Weichenthal et al. [12], who observed the spatial distribution of ultrafine particles in Toronto, Canada, found that parks and open spaces seemed to lower the concentration of ultrafine particles. In addition, Farrel et al. [13] investigated that waterfront areas seemed to have lower PM 2.5 concentration. Rivera et al. [14], who analyzed the spatial distribution of PM2.5, showed that higher density of residential areas, correlated with higher concentration of PM2.5. In particular, economically disadvantaged groups and social minority groups were more likely to live in areas with high air pollution, thus seriously harming their health [15]. Consequently, it is important to understand the relationship between socio-economically disadvantaged groups and their exposure to air pollution [16]. These Environmental inequalities can have critical negative influences on socio-economically disadvantaged minority group’s health. Hence, these issues deprive the need for continued attention and research on air pollution.

3. Methods

3.1 Study Area and Air-monitoring Stations

Seoul Metropolitan City, the capital of Korea, has a population of around 9.9 million people as of 2020 and a population density of 16,375 people per square kilometer. Seoul’s land area (605.68 ㎢) remains mostly for residential use (53.58 %), followed by parks and open spaces (38.69 %), commercial uses (4.24 %), and industrial uses (3.28 %). Figure 1 shows the locations of monitoring stations of air pollutants that are distributed across Seoul Metropolitan City. Seoul has 46 air-monitoring stations in operation, including 31 urban and 15 roadside airmonitoring stations. One out of 46 air-monitoring stations is located outside of Seoul, but it is still located relatively close to Seoul. The height of air-monitoring stations is deliberately set in the range between 1.0 m to 10 m above the ground. Spatial information on air-monitoring stations and air pollutant concentrations were obtained from the integrated air environment information system, which provides highly reliable measurement data on the outdoor air quality levels nationwide under the Korean Ministry of Environment [17]. Finally, this study examined the spatial distribution of air pollution concentrations in the 25 autonomous districts (Gu) of Seoul Metropolitan City by the different types of air pollutants and is expected to help establish air pollution prevention policies for each autonomous district in Seoul in the future.

Figure 1. Air-monitoring stations in Seoul

3.2 Spatial Measures of Air Pollutants

In Korea, air pollutants officially measured by the Air Korea under the Korean Ministry of Environment are fine dust (PM10), ultrafine dust (PM2.5), ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), and sulfur dioxide (SO2). This study examined the annual average of the concentrations of the six air pollutants provided by the Seoul Air Quality Information System. First, 46 air-monitoring stations in Seoul were geocoded with the use of the geocoding tool of GIS. Next, the 2018 average concentrations of six air pollutants (PM10, PM2.5, NO2, CO, SO2, O3) measured at each air-monitoring station were spatially joined with the data of each air-monitoring station. The GIS base map was first rasterized in units of 50 m × 50 m to measure the concentrations of air pollutants more precisely. An inverse distance weighted (IDW) interpolation was performed to measure the air pollution concentration [18]. This method is an appropriate analysis by GIS to reasonably calculate the values of unmeasured points [19]. Finally, the air pollution concentrations by the different types of air pollutants from the IDW interpolation were measured at the autonomous district (Gu) level through the GIS zonal statistics tool.

4. Results

4.1 Descriptive Statistical Analysis of Air Pollutants

Table 1 shows the descriptive statistics of the air pollutants. The average concentrations of air pollutants were calculated based on the average of all the administrative districts (Gu) in Seoul. The average concentrations of PM2.5 and PM10 in Seoul were 23.85 and 42.31 μg/m³,

respectively. These concentration levels were more than double the WHO’s recommended PM2.5 and PM10 annual averages of 10 and 20 μg/m³, which indicates that Seoul ’s particulate matter contamination was very serious in 2018. PM2.5 and PM10 include inhalable particles that are small enough to penetrate the thoracic region of the respiratory system. According to the WHO report [20], for the health of Seoul citizens, there is an urgent need for effective and practical policies to reduce PM2.5 and PM10 for the environment and public health. Particulate matters are air pollutants that have a serious negative influence on people's health. Furthermore, the average concentrations of NO2, CO, O3, and SO2 were 0.032, 0.545, 0.021, and 0.005 ppm, respectively. The NO2 concentration was also higher than the WHO standard of 0.021 ppm.

Table 1. Descriptive statistics

Air pollutant Unit Mean Std. Dev Min. Max. WHO standard

PM2.5

PM10

NO2

CO

O3 SO2 μg/m³ μg/m³ ppm ppm ppm ppm

23.85 42.31 0.032 0.545 0.021 0.005 1.389 2.447 0.004 0.040 0.002 0.000 21.73 38.14 0.022 0.421 0.018 0.004 27.50 47.18 0.036 0.607 0.025 0.006

10 20 0.021 n/a n/a n/a

4.2 Spatial Distribution of Air Pollutants

Figures 2–7 show the spatial distributions of the air pollutants measured in an autonomous district (Gu) in the Seoul Metropolitan City through spatial interpolation. Overall, the GIS maps demonstrated that there were spatially significant differences in the air pollution concentrations depending on the type of air pollutants. In other words, it suggested that regional characteristics in Seoul have different effects on each air pollutant. Therefore, it means that it is necessary not only to make efforts to reduce air pollution generally in Seoul, but also to reduce air pollution within each autonomous districts (Gu). Looking at the spatial distribution of each air pollutant, PM2.5 shows a high concentration level in the western regions of Seoul, and relatively low concentration level in the northern and eastern regions. Although the spatial distribution of PM10 is slightly different from that of PM2.5, it shows a similar spatial distribution pattern. The NO2 concentration appeared to be partially and evenly high throughout Seoul. Interestingly, the spatial distribution of O3 concentration seems to be opposite to that of NO2, although both O3 and NO2 are serious air pollutants harmful to humans. It is necessary to establish resilient and effective environmental policies according to the degree of negative impacts of air pollutants on humans for each type of air pollutant. The CO concentration was high in the eastern and southern regions. SO2 showed spatial distribution similar to those of PM2.5 and PM10. Finally, the fact that all air pollutants have different influences by spatial characteristics by regions requires more in-depth research and policy development on regional effects depending on the type of air pollutants in the future.

Figure 6(a). Spatial distribution of O3 Figure 6(b). Spatial distribution of O3

Figure 7(a). Spatial distribution of SO2 Figure 7(b). Spatial distribution of SO2

4.3 Correlation Analysis Between Air Pollutants

As shown in Figure 2–7, PM2.5 and PM10 are the same type of air pollutants, but their spatial distributions are different. This result suggests the need of examining the correlation between air pollutants to establish a more effective air pollution reduction plan. Table 2 shows the result of correlation analysis between various air pollutants. PM2.5 and PM10 are air pollutants of the same nature and showed a very high correlation coefficient (r = 0.835, p < 0.01). However, a high negative correlation coefficient (r = –0.727, p < 0.01) was found

between NO2 and O3. NO2 had a moderate positive correlation with PM10 (r = 0.556, p < 0.01), and SO2 had a moderate positive relation with PM2.5 (r = 0.605, p < 0.01). Air pollutants other than CO had a positive or negative correlation with each other, whereas CO had no correlation

Table 2. Correlation analysis

PM2.5

PM10

NO2

CO

O3

SO2

PM2.5 PM10 NO2

1 0.416*

–0.287 0.044 0.190 –0.061

1 –0.727** 0.403* 0.556**

0.199

1 –0.254 –0.480* –0.405*

CO O3 SO2

1 0.835** 0.605**

1 0.420*

* p < 0.05, ** p < 0.01

with other air pollutants. Therefore, it can be inferred that the pollutant source of CO is different from that of other air pollutants.

5. Conclusion

Air pollution negatively affects people’s health and the quality of life. Therefore, many countries around the world have made various efforts to reduce air pollution and protect the environment. Korea has also recently come up with various policies and interventions to reduce air pollution. In addition, since air pollution has spatial properties, there are differences in the concentration of air pollutants depending on the region. Therefore, this study examined the spatial distribution of air pollutants and analyzed the correlation between various air pollutants in Seoul, Korea. The main results are as follows. First, the concentrations of air pollutants in Korea are generally higher than the WHO air quality standards. In particular, the concentration levels of PM2.5 and PM10 were more than double the WHO standards. Therefore, Seoul needs to pay continuous attention to sustainable policies to reduce air pollution. Second, this study proves regional differences in air pollution concentration depending on the type of air pollutants. This means that each local government as well as the Seoul Metropolitan Government must make an effort to effectively reduce air pollution. Third, there is a high correlation between various air pollutants. This suggests that it is necessary to develop more effective pollution reduction policies by understanding the causal properties of air pollutants. The urban facilities, environments, and services provided by the urbanization process of the city allowed for comfortable life. However, side effects such as air pollution from aimless and careless urbanization caused great harm to human life. Therefore, it is necessary to improve quality of life through constant efforts to reduce air pollution.