## 2 Materials and Methods
### Measurement of PM and Weather Factors Based on Mist Spraying  
Analyzing the characteristics of PM reduction due to mist spraying requires measuring PM concentration using a mobile PM measuring device (Turnkey, UK, \(\pm\)0.5% accuracy). The Dustmate is a lightweight portable version of the Osiris laser light scattering particulate monitor that is capable of measuring total suspended particulates (TSP), PM10, PM2.5, and PM1 with a resolution of 0.1 ug/m\({}^{3}\). Air is drawn into the instrument at a rate of 0.6 L/min, and the flow is configured so that only one particle is illuminated by the laser light beam (670 nm) at any particular moment in time [30]. The use of a Dustmate to measure PM concentrations has been successfully demonstrated in previous studies [31; 32; 33]. A Dustmate measures real-time PM concentration using the light-scattering method. However, humidity interferes with the light-scattering method, resulting in overestimating PM concentration [30; 34]. Thus, we excluded the PM data when humidity values were over 80% to prevent overestimating PM concentration [35]. In addition, we used silica gel, a moisture absorbent, to prevent moisture from entering the Dustmate. However, the silica gel was not large enough to change the inflow rate; hence, we ignored its impact. As mist is heavily influenced by wind. The measuring points in the YCF and CRP were selected based on the main wind direction of each park (Figure 2). In YCF, where the main wind is the northwest wind, the PM was measured at YCF-1 (37\({}^{\circ}\)28\({}^{\prime}\)13.73\({}^{\prime\prime}\) N, 127\({}^{\circ}\)27\({}^{\prime}\)15.49\({}^{\prime\prime}\) E), YCF-2 (37\({}^{\circ}\)28\({}^{\prime}\)13.73\({}^{\prime\prime}\) N, 127\({}^{\circ}\)27\({}^{\prime}\)14.80\({}^{\prime\prime}\) E), and YCF-3 (37\({}^{\circ}\)28\({}^{\prime}\)13.95\({}^{\prime\prime}\) N, 127\({}^{\circ}\)27\({}^{\circ}\)24.18\({}^{\prime\prime}\) E) (n = 3). In CRP, which is strongly affected by the west wind, we measured PM concentration at CRP-1 (37\({}^{\circ}\)31\({}^{\prime}\)12.20\({}^{\prime\prime}\) N, 127\({}^{\circ}\)35\({}^{\prime}\)0.19\({}^{\prime\prime}\) E), CRP-2 (37\({}^{\circ}\)31\({}^{\prime}\)12.07\({}^{\prime\prime}\) N, 127\({}^{\circ}\)35\({}^{\prime}\)0.06\({}^{\prime\prime}\) E), and CRP-3 (37\({}^{\circ}\)31\({}^{\prime}\)11.82\({}^{\prime\prime}\) N, 127\({}^{\circ}\)34\({}^{\prime}\)9.91\({}^{\prime\prime}\) E) (n = 3). A Dustmate was installed 1.5 m above the ground, considering the average breathing height of humans. Three devices simultaneously recorded the PM values at three points in YCF and CRP sites. We focused on the change in PM concentration before and after mist spraying; thus, we did not include control treatments. Mist spraying and PM measurements were carried out intensively in May when high PM concentrations occurred, and citizens actively enjoyed outdoor activities. Considering that the visitation rate of citizens in each park was high, mist spraying was conducted as follows: the mist was sprayed thrice at 30-min intervals during lunch (11:00-13:00) and evening rush hour (17:00-19:00) [YCF], morning rush hour (08:00-10:00), and lunch and evening rush hour [CRP] (5 min per spraying period). At YCF, the concentrations of PM\({}_{10}\) (ug/m\({}^{3}\)), PM\({}_{2.5}\) (ug/m\({}^{3}\)), and PM\({}_{1.0}\) (ug/m\({}^{3}\)) were measured on May 6 (evening rush hour) and May 7 (lunch), 2020. At CRP, PMx concentrations were measured on May 7 (evening rush hour) and May 8 (morning rush hour and lunch), 2020. Furthermore, PM data were measured at intervals of 1 s; these data were used at an average of 5 min. As light mist particles can diffuse rapidly into the air soon after spraying, we speculated that the PM reduction effect of mist would occur in a short time [2] and would concentrate on changes in PM concentration before (10 min), during (5 min), and after (10 min) mist spraying.