Pollution Remediation by Urban Forests: PM2.5 Reduction in Beijing, China

We based our research on real-time monitoring data for PM2.5 at the Beijing Municipal Environmental Protection Monitoring Center of Haidian Beijing Botanical Garden (a vegetated area), and at Haidian Wanliu (a non-vegetated area). By combining these two data points with the PM2.5 and meteorological data from a separate monitoring station in Beijing Botanical Garden's forest interior, we analyzed the daily fluctuation, regional variation, and foliar adsorption characteristics of PM2.5 in varied environments (Feb.-Dec. 2013 and Jan.-Feb. 2014). Our results show a double peak and valley pattern of PM2.5 daily variation and daytime values greater than nighttime measurements. Average annual PM2.5 concentration values at different monitoring stations were Haidian Wanliu (100.61 +/- 26.49 mu g.m(-3)), greater than at the Beijing Botanical Garden forest interior monitoring station (89.72 +/- 23.49 mu g.m(-3)), and both greater than at Haidian Beijing Botanical Garden (77.72 +/- 23.37 mu g.m(-3)). The maximum PM2.5 concentrations during 12 months were all in Haidian Wanliu (non-vegetated area), while the minimums were all in Haidian Beijing Botanical Garden (vegetated), Haidian Wanliu being 83.33% of the time higher in PM2.5 concentration than Beijing Botanical Garden forest interior. Possibly because of the trees, PM2.5 concentrations in the forest area were lower than that in the non-vegetated area. We find an average PM2.5 adsorption capacity per unit leaf area of 0.048 +/- 0.031 mu g.cm(-2) 0.645 +/- 0.034 mu g.cm(-2) in May, and 0.058 +/- 0.006 mu g.cm(-2) -0.887 +/- 0.014 mu g.cm(-2) in June for the 10 tree species included in our study. Of these 10, incense Cedrus deodara evidences the greatest adsorption and Sophora japonica shows the minimum. As a whole, conifers adsorb at 1.32 times the rate of broadleaf tree species, according to our data. PM2.5 adsorption capacity was greater in June (0.294 +/- 0.227 mu g.cm(-2)) than in May (0.215 +/- 0.184 mu g.cm(-2)). Daily and annual variation in different regions falls into a pattern where Haidian Wanliu pollution is greater than Beijing Botanical Garden forest interior monitoring station, and both are greater than Haidian Beijing Botanical Garden, which confirms the forest ecosystem's involvement. It appears that the forest has many functions, including atmospheric purification by adsorption of PM2.5 and other particulates as evidenced by better air quality in forest areas than in non-vegetated sites. Furthermore, forest clearings show better air quality than the forest interior.