Spatial and diurnal variations of negative air ions concentrations and their influencing factors in Guancen Mountain

Negative air ions (NAIs) are beneficial for human health and crucial for supporting vegetation configuration in local health and wellness tourism development. To determine differences in NAIs concentrations among forest, meadow, and wetland environments in the Guancen Mountain region, 25 plots were selected and classified into three vegetation types, paving, turf, and woods. NAIs, air temperature (Ta), relative humidity (RH), PM 2.5 and PM 10 were monitored, and their relationships were analyzed statistically. Woods vegetation showed higher NAIs than turf and paving. The diurnal variation in NAIs concentration exhibited ∩-shaped, U-shaped and gradually rising patterns. Generally, the ∩-shape pattern appeared in wetlands with open woods, and peaked from 12:30 to 14:00. The U-shape was consistently observed in forests with dense plant communities, with peaks in the morning and evening, and decreasing at noon. A consistent pattern of gradual rise was observed in open spaces during the daytime, peaking between 17:00 and 18:00. A positive correlation between Ta and NAIs concentrations was observed in low altitude areas (1,400–1,600 m), whereas a negative correlation was observed in high-altitude areas (>1700 m). The regression analysis and Random Forest algorithm indicated that the primary influencing factor for paving and turf vegetation types was Ta, whereas PM 2.5 and PM 10 were the primary influencing factors for woods vegetation types. Overall, the optimal conditions for NAI concentration were broadly in the range of 20–30 °C, RH of 40%–70%, and PM 2.5 < 20 μg/m 3 .