Variation characteristics of negative oxygen ions distribution in Yangzhou urban forest and its relationship with meteorological factors

【Objective】This study aimed to analyze the spatial and temporal variation of air negative oxygen ion con-centration in Yangzhou urban forests,and to provide a theoretical basis for the understanding of air negative oxygen ion resources in urban forests of Yangzhou.【Method】Relying on the Jiangsu Yangzhou Urban Forest Ecosystem National Monitoring and Research Station,the study focused on Songjiacheng Sports and Leisure Park (urban forest),Mastixia Bay Scenic Area (suburban forest),and Runyang Wetland Forest Park (distant urban forest).Data on negative air ion concentrations and forest meteorological factors were collected from these three regions from January to December 2020.The differences in negative air ion concentrations between different seasons were compared,the correlation between nega-tive air ion concentrations and meteorological factors was analyzed,and the contribution rates of various meteorological factors to air negative ion concentrations were analyzed using enhanced regression trees.Structural equation modeling was used to analyze the direct and indirect effects of various meteorological factors on negative oxygen ion.【Result】In the suburban forest area of Yangzhou,the diurnal variation of negative oxygen ion concentration displayed a unimodal pattern.The monthly change trend of urban suburban forest matched consistently with the peak values occurring in April and June.The seasonal average negative oxygen ion concentration in suburban forest was spring>winter>summer>autumn,and the average negative oxygen ion concentration in suburban forest was summer>winter>spring>autumn.The annual average value of negative oxygen ion concentration (666.87 ions/cm³) and canopy density (0.80) were lower than those in urban forest and suburban forest,and the higher canopy density,the smaller the coefficient of variation of negative oxygen ion concentration.There was a significant (P<0.05,the same below) or extremely significantly (P<0.01,the same below) correlation between the concentration of air negative oxygen ions and wind speed,air pressure,air temperature,and PM_2.5 in the urban forest area,whereas the concentration of negative oxygen ions in suburban forest and distant urban forest had a significant or extremely significant correlation with barometric pressure,wind speed,air temperature,air hu-midity,PM_2.5,illumination intensity,and other in-forest meteorological elements.The contribution of meteorological fac-tors to the concentration of negative oxygen ions in the air,as well as structural equation modeling,was selected for the urban distant suburban forest.The results showed that air humidity contributed the most to the concentration of negative oxygen ions in spring (38.51%) and autumn (47.58%),while PM_2.5 contributed the most to the negative oxygen ions in summer (27.87%) and winter (38.51%).Air humidity had a direct positive effect on negative oxygen ion concentration,while illumination intensity had a direct negative effect on negative oxygen ion concentration,and wind direction had an indirect effect on negative oxygen ion concentration by changing PM_2.5.【Conclusion】The pattern of change of negative oxygen ion concentration in forests in different regions of Yangzhou is different,and different seasons and times have ob-vious effects on the negative oxygen ion concentration.According to the difference of negative oxygen ions in different areas and the seasonal change rule of its performance,different park tour plans can be developed,it is recommended to go to the distant urban forest in the summer,and to the suburban forest in the spring tour.