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

To increase our knowledge of PM concentrations near the surface in a forest park in Beijing, an observational study measured the concentration and composition of PM 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 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 in the forest was highest during winter, followed by spring and fall, and was lowest during summer. The main chemical components of PM near the surface in the forest were SO and NO , which accounted for 68.72% of all water-soluble ions that we observed. The concentration of PM 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.