Understanding PM_2.5 concentration and removal efficiency variation in urban forest park-Observation at human...

To increase our knowledge of PM_2.5 concentrations near the surface in a forest park in Beijing, an observational study measured the concentration and composition of PM_2.5 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 PM_2.5 near the surface peaked at 07:00-09:30 and reached their lowest at 12:00-15:00. Besides, the results showed that the annual concentration of PM_2.5 in the forest was highest during winter, followed by spring and fall, and was lowest during summer. The main chemical components of PM_2.5 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 PM_2.5 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 07:00 and 09:30 in summer, while the lowest occurred between 09:30 and 12:00 in winter.