Abstract: To clarify the responses of negative air ion (NAI) concentration in urban forests to temperature changes, four urban forest parks in Beijing were used as the research objects, including Beijing Chaoyang Park (central urban area), Nanhaizi Country Park (suburban wetland area), Xishan National Forest Park (suburban shallow mountain forest area), and Songshan National Nature Reserve (outer suburban mountain forest area). The responses of NAI concentration to temperature during 2017-2020 were analyzed using continuous dynamic observation data from NAI monitors and automatic weather stations in forest ecological environment monitoring stations. The results showed that NAI concentration in the central urban area was negatively correlated with the changes of hourly temperature in each season during the four years, with NAI concentration and temperature reaching the lowest and highest values at 14:00-15:00, respectively. In suburban shallow mountain forest area and suburban wetland area, there was a positive correlation between NAI concentration and temperature in spring, autumn, and winter, but a negative correlation between NAI concentration and temperature in summer. At the month scale, NAI concentration in each urban forest area was positively correlated with temperature, but the response of NAI concentration to temperature in the outer suburban mountain forest area had a hysteresis. At the annual scale, NAI concentration was significantly positively correlated with temperature (P<0.01). In 2020, when temperature was 0-10 ℃, the negative correlation between NAI concentration and temperature in the suburban shallow mountain forest area was the strongest (r=-0.441). At 10-20 ℃, there was a very significant negative correlation between NAI concentration and temperature in the suburban shallow mountain forest area (r=-0.253), while a positive correlation in the outer suburban mountain forest area. When temperature was between 20-30 ℃, there was a significant negative correlation between NAI concentration and temperature in the suburban wetland area and the outer suburban mountain forest area. The correlations between NAI concentration and other meteorological factors (wind speed and solar radiation) in different urban forest areas in 2020 showed seasonal variations. In spring, the NAI concentration in the suburban wetland area was significantly positively correlated with solar radiation. In summer, there was a negative correlation between NAI concentration and wind speed in the suburban shallow mountain forest area, and a negative and positive correlation between NAI concentration and solar radiation in the suburban shallow mountain forest area and the outer suburban mountain forest area. In autumn, NAI concentration was significantly positively correlated with solar radiation in the outer suburban mountain forest area. In winter, NAI concentration was significantly positively correlated with solar radiation in the central urban area and negatively correlated with solar radiation in the outer suburban mountain forest area.

Key words: urban forest, negative air ion, temperature, correlation.