Characteristics and Interaction of Negative Air Ions and Ozone in Beijing Urban Forest

We select negative air ions and ozone data monitored for a long time by 4 urban forest ecological environment monitoring stations in Beijing, including Beijing Sun Park in the center, Nanhaizi country park which is suburban development zone, Beijing Xishan forest park which is suburban shallow mountain forest area and Beijing Songshan National Nature Reserve which is in the outer suburbs, to study and analyze their spatial and spatiotemporal variations and the interaction. The results show that the average NAI and O₃ concentrations in Beijing urban forest were higher in summer than in winter, and the diurnal variation of air negative ion concentration in summer and winter presented 'single peak single valley' and 'single peak' curves respectively. The diurnal variation trend of O₃ concentration in the 2 seasons shows a 'single peak single valley' curve; in summer, air negative ion concentration peaks at 7: 00–9: 00 and valleys at 15: 00, and peaks at 12: 00 in winter. The summer and winter O₃ concentration valley value in 7: 00–9: 00, the winter peak at 15: 00, about 2 hours earlier than the summer. In terms of spatial changes, the urban pollution gradient has no significant influence on the spatial change of air negative ion concentration, the air negative ion concentration changes in summer are as follows: downtown park > outer suburb park > suburban shan-forest area > suburban development zone, the same pattern also appears in winter; the O₃ concentration gradually decreases from the downtown park to the outer suburbs park, which is greatly affected by the gradient of urban pollution. NAI concentration was negatively correlated with O₃ concentration in summer, and positively correlated with O₃ concentration in winter, indicating that plant growth affects the correlation between the two.