Abstract:

In recent years, negative air ions have received wide attention due to the effects of directly reflecting air quality, increasing air comfort and improving human physiological function. In this study, the long-term observation data of negative air ion concentration (NAIC), Nitrogen oxide (NO_x) concentration and meteorological factors were collected from an urban forest ecological environment monitoring station located in Xishan National Forest Park in Beijing. We are aiming to explore the temporal and spatial dynamic changes and correlations among these parameters, and further provide reference for forest health planning and air control measures. The results show that: (1) NAIC and NO_x concentrations were significantly different in different seasons. NAIC was as follows: summer [(2272.24±250.57) ion∙cm^-3]>spring [(1777.28±60.06) ion∙cm^-3]>autumn [(1628.72±248.61) ion∙cm^-3]>winter [(1240.86±169.49) ion∙cm^-3]. The concentration of NO_x was as follows: winter [(132.89±37.57) μg∙m^-3]>autumn [(71.58±8.66) μg∙m^-3]>spring [(34.41±8.89) μg∙m^-3]>summer [(9.74±5.85) μg∙m^-3]. In spring and winter, they presented negative correlations between each other (R²= -0.671, R²= -0.420). (2) Under sunshine condition, NAIC usually peaks around 14:00 [(1899.79±14.39) ion∙cm^-3], while NO_x concentration was lower in daytime than nighttime. (3) Under rainy condition, NAIC showed a trend of unimodal curve, with heavy rain [(2593.95±760.34) ion∙cm^-3]>light rain [(1817.15±149.29) ion∙cm^-3]>no rain [(1785.22±141.72) ion∙cm^-3]. NO_x concentrations remained unchanged with a smooth curve under rainy condition, but showed a trend of bimodal curve under no rain condition, with concentrations as follows: no rain [(30.38±16.11) μg∙m^-3]>light rain [(12.04±2.26) μg∙m^-3]>heavy rain [(10.08±6.36) μg∙m^-3]. (4) Under windy condition, NAIC increased with wind speed, with moderate breeze (2069.99 ion∙cm^-3, 6.2 m∙s^-1)>gentle breeze (2022.63 ion∙cm^-3, 4.8 m∙s^-1)>light breeze (1928.51 ion∙cm^-3, 2.9 m∙s^-1); The concentrations of NO_x decreased with the increased of the wind speed. In conclusion, urban forest can improve the structure of forest green space and increase NAIC through the purification effect of NO_x to affect the correlation between these two air quality indicators.

Key words: Beijing Xishan National Forest Park, urban forest, negative air ion, NO_x, typical weather conditions, correlation

摘要：

空气负离子能直观地反映空气质量,可以增加空气的舒适性且对人体生理功能有积极影响。利用位于北京西山国家级森林公园的城市森林生态环境监测站长期定位观测数据,包括空气负离子浓度（NAIC）、氮氧化物（NO_x）浓度和气象因子等,探究其时空动态变化及彼此相关性特征,为城市森林康养规划及大气治理措施提供参考。研究结果表明,（1）NAIC和NO_x质量浓度季节差异显著,NAIC表现为夏季[(2272.24±250.57) ion∙cm^-3]>春季[(1777.28±60.06) ion∙cm^-3]>秋季[(1628.72±248.61) ion∙cm^-3]>冬季[(1240.86±169.49) ion∙cm^-3];NO_x质量浓度表现为冬季[(132.89±37.57) μg∙m^-3]>秋季[(71.58±8.66) μg∙m^-3]>春季[(34.41±8.89) μg∙m^-3]>夏季[(9.74±5.850) μg∙m^-3];两者在春、冬两季呈负相关关系（R²= -0.671,R²= -0.420）。（2）晴天条件下,NAIC通常于下午14:00左右达到峰值[(1899.79±14.39) ion∙cm^-3];NO_x质量浓度白天低于夜间。（3）降水条件下,NAIC呈单峰曲线,表现为大雨[(2593.95±760.34) ion∙cm^-3]>小雨[(1817.15±149.29) ion∙cm^-3]>无雨[(1785.22±141.72) ion∙cm^-3];在雨天NO_x质量浓度基本一致,为平缓曲线,无雨条件下为双峰曲线,具体表现为无雨[(30.38±16.11) μg∙m^-3]>小雨[(12.04±2.26) μg∙m^-3]>大雨[(10.08±6.36) μg∙m^-3]。（4）起风条件下,NAIC随风速增加而增大,表现为和风 (2069.99 ion∙cm^-3, 6.2 m∙s^-1)>微风 (2022.63 ion∙cm^-3, 4.8 m∙s^-1)>轻风 (1928.51 ion∙cm^-3, 2.9 m∙s^-1);NO_x浓度则受风力抑制,浓度降低。综上所述,城市森林通过对NO_x的净化作用,可改善森林绿地结构、提高NAIC,从而影响二者的相关性。

关键词: 北京西山国家森林公园, 城市森林, 空气负离子, NO_x, 典型天气, 相关性