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Negative air ions (NAIs) benefit the mental and physical health of humans,but rapid urbanization can decrease the abundance of NAIs.Quantifying the spatial and seasonal distribution of NAIs and determining the factors that influence the concentration during urbanization is thus essential.In the present study of a typical developing urban district in southern China,negative air ion concentrations (NAICs) in 60 forests sites and 30 urban green spaces were quantified on seven consecutive days in each of the four seasons.Large seasonal variations in NAIC were revealed in forests and urban green spaces with trough values in summer.NAIC progressively decreased from forests to urban green spaces and was influenced by local land morphology,vegetation characteristics,and climatic factors.The vast,heavily vegetated northeastern region was the richest area for NAIs,whereas the narrow central region (urbanized area)was the poorest,implying dramatic impacts of urbanization on the spatial distribution of NAIs.The relationship between air temperature and NAIC was better fitted with a quadratic equation than a linear equation.Moreover,the NAIC was more sensitive to local morphology in urban green spaces than in urban forests,indicating the vulnerability of NAIs in urbanized areas.Therefore,the appropriate design of local urban morphology is critical.