*2.2. Measurement Method*

The PM<sup>10</sup> and PM2.5 concentrations were measured by a mobile PM measuring device, Dustmate (Turnkey, UK, ±5% accuracy), which was installed 1.5 m above the ground. The use of Dustmate for analyzing PM concentrations proved to be successful in studies [20,21]. Dustmate is a real-time PM mass concentration meter that uses the light scattering method. The Sihwa Industrial Complex is a coastal area and is highly influenced by onshore winds. Thus, Dustmate is suitable for checking varied PM concentrations in real time and can measure at high concentrations. However, in the case of the light scattering method, the concentration can be overestimated because the material can cause interference in light transmission, which could be highly influenced by humidity [22]. We excluded the PM concentration data with humidity values over 80% to avoid overestimation of PM concentrations

due to binding effects of vapor particles and particulate matter. PM monitoring was conducted from April to October 2019; citizens in Korea usually visit urban green areas and enjoy the outdoors during this season. We measured the PM concentration in the morning rush hour (7–9 h), around noontime (11–13 h), and during evening rush hour (16–18 h), considering the peak hours with a large transient population. We measured data at intervals of 1 s and used these data as averages of 5 min. Based on these PM concentration data, we calculated the time mean, monthly average, and reduction rates of PM as follows:

$$\text{PM reduction rate} \left(\% \right) = 100 \times \frac{\text{C}\_{\text{IC}} - \text{C}\_{\text{RA}}}{\text{C}\_{\text{IC}}} \tag{1}$$

where *CIC* is PM concentration in IC and *CRA* is PM concentration in RA.

**Figure 1.** The location of measuring points and national atmospheric environmental research station in Siheung City, Gyeonggi-do, Republic of Korea (modified from map.kakao.com). IC: industrial complex; UG: urban green area; RA: residential area; Airkorea-IC: national atmospheric environmental research station located near IC; Airkorea-RA: national atmospheric environmental research station located near RA.

In order to identify the seasonal patterns of PM reduction by UG, the relationship between PM, meteorological factors, and air pollutants was analyzed. We used a portable weather meter to measure temperature, wind direction, wind speed, and humidity at each point for 24 h. Since the Dustmate equipment could not measure the concentrations of air pollutants (ozone (O3), NO2, SO2, carbon monoxide (CO)), these concentrations were measured by the national atmospheric environmental research stations located nearby in IC (Airkorea-IC; 37◦20′N, 126◦43′E) and RA (Airkorea-RA; 37◦20′N, 126◦44′E) (Figure 1). We hypothesized that the values from those stations could represent the air pollutant concentrations for the measuring points.
