Daily dynamics of forest air negative ion concentration in spring and the relationship of influencing factors: results of field monitoring

Negative air ions (NAIs) are important in improving air quality and developing new materials and clinical medicine. NAI concentrations are higher in urban forests than in other areas, which is good for public health. The Hualou Scenic Area in Qingdao Laoshan National Forest Park was the study site in this paper. Ten plant communities’ ecological health factors (NAI, temperature, relative humidity, light, wind speed, and particulate matter) were measured concurrently, and plant factors within them were investigated. The Origin, R, and SPSS software were all used to analyze the daily dynamic patterns of NAI concentrations, the relationship between NAI and other ecological health factors, and plant factors. Results showed that (1) during spring field monitoring, NAI levels in Hualou Scenic spot maintained a high level. The concentration of NAI in the air is the highest from 16:30 to 18:00. This may be due to the gradual reduction of light in the late afternoon, when the plant’s hibernation is broken, leaf stomata open, and NAI levels in the environment peak; (2) influenced by species richness and compound environment, hillside mixed forests have higher levels of NAI and more environmental advantages than other forests; (3) Mantel test analysis of NAI with other ecological health factors revealed that changes of NAI were negatively correlated with wind speed (p<0.05), PM_2.5, and PM₁₀ (p<0.001), and positively correlated with temperature, relative humidity (p<0.001), and noise (p<0.05); (4) multiple factors influence the spatial distribution and dynamics of forest ecological health factors. The study chose 13 plant community variables as benchmarks for principal component analysis, and the results can be comprehensively interpreted by four principal components: plant biotypes, stand structure characteristics, geographic characteristics, and spatial characteristics. Correlation analysis showed that the richer the forest flora and the higher the level of community structure, the greater the influence on NAI (p<0.05). Green space management departments can enhance the functional spatial layout and optimal control of forest vegetation based on the influence of negative air ion concentration and spatial and temporal distribution characteristics to improve the ecological and recreational function gathering of urban forests.