Spatial variability and pollutant-specific mitigation effects of an urban vegetated park observed with a high-density...

Urban vegetation is often considered a strategy for improving urban air quality, yet its effectiveness depends on pollutant characteristics and spatial scale. In this study, a high-density air quality sensor network was deployed to characterize the spatial and temporal variability of multiple pollutants inside and outside an urban vegetated park in a dense metropolitan environment in Daegu, Republic of Korea. Measurements across roadside, park interior, single-tree canopy, and rooftop locations enabled evaluation of exposure-relevant contrasts at fine spatial scales. Primary traffic-related gases (CO, NO, and NO₂) consistently showed lower concentrations inside the park than at roadsides, indicating that the park interior can function as a relatively clean microenvironment for these pollutants. In contrast, ozone concentrations were higher inside the park due to strong NO-driven chemical loss at roadsides, suggesting that, under high ozone conditions, potential human exposure inside vegetated parks should be carefully considered. PM_2.5 exhibited weak inside-outside contrasts, indicating that regional transport and secondary formation dominated over local mitigation effects. These results suggest that the limited PM_2.5 reduction observed in this study is partly attributable to the small spatial extent of the park, highlighting the importance of vegetation area, density, and continuity for effective PM_2.5 exposure mitigation. In contrast, ultrafine particles showed substantially larger reductions within a single-tree canopy, underscoring the potential of vegetation to mitigate particle number concentrations.