Understanding PM2.5 concentration and removal efficiency variation in urban forest park-Observation at human breathing height.

ABSTRACT

To increase our knowledge of PM2.5 concentrations near the surface in a forest park in Beijing, an observational study measured the concentration and composition of PM2.5 in Beijing Olympic Forest Park from 2014 to 2015. This study analyzed the meteorological factors and removal efficiency at 1.5 m above the ground (human breathing height) over the day in the forest. The results showed that the average concentrations of PM2.5 near the surface peaked at 0700-0930 and reached their lowest at 1200-1500. Besides, the results showed that the annual concentration of PM2.5 in the forest was highest during winter, followed by spring and fall, and was lowest during summer. The main chemical components of PM2.5 near the surface in the forest were SO4 2- and NO3 -, which accounted for 68.72% of all water-soluble ions that we observed. The concentration of PM2.5 in the forest had a significant positive correlation with relative humidity and a significant negative correlation with temperature. The removal efficiency near the surface showed no significant variation through the day or year. In the forest, the highest removal efficiency occurred between 0700 and 0930 in summer, while the lowest occurred between 0930 and 1200 in winter.