How to evaluate the reduction effect of the park on PM2.5? Exploratory application of the maximum and cumulative perspective

Urban parks have been widely proved to be effective in reducing particulate matter pollution, but there is still a knowledge gap in quantitatively evaluating their reduction effects. The purpose of this study is to develop a new method to quantify the reduction effect of PM_2.5 in urban parks through high-precision spatio-temporal monitoring experiments in 22 typical urban parks in Shenyang, China, so as to fill this gap. In this study, the cubic polynomial function model was used for the first time to establish the relationship curve between PM_2.5 concentration inside and outside the park at different distances. The results showed that the park PM_2.5 reduction magnitude and distance were about 5.04–10.14 ug/m³ and 149.47–150.19 m, respectively. Partial correlation analysis revealed that the relationship between the reduction evaluation indexes and the environmental factors had time heterogeneity. The park's internal characteristics and surrounding building environment was the key factor affecting the park PM_2.5 reduction effect. In addition, parks smaller than 4.71 hm² demonstrated better PM_2.5 reduction efficiency. In conclusion, this study provides a new quantitative approach to evaluating the park PM_2.5 reduction effect and offers data-driven insights for optimizing park planning to enhance the permeability of these effects beyond park boundaries.