In this study, six types of urban green land in Beijing Olympic Park, including grassland, shrub, conifer, broadleaf tree, mixed trees, and a control, were selected to study the relationship between urban green land and particulate matter (PM). For all particles – coniferous tree forest type, broadleaf tree forest type, and broadleaf and coniferous mixed trees type – the common point was that they have big leaf areas that can absorb a large number of particles. So the concentrations in the three forest types were very low. Leaf area is a big factor for absorbing and reducing concentrations of four types of particles.
The concentrations of PMs with the four particle sizes were lower in summer than in other seasons. For TSP and PM₁₀, the concentrations were significantly higher in September and November than in other months. The differences between summer, autumn, and winter were insignificant. For PM_2.5 and PM1, the concentrations in autumn were higher than in other seasons. In summer, PM_2.5 and PM₁ concentrations were significantly lower than in other seasons, especially in August and October.
The daily variation of particulate matter formed a “double-apex” curve, with PM concentrations higher at dawn and dusk and lower at noon. In comparison with dusk, concentration was normally lower at dawn. At night and dawn, there were usually very high levels of PM, perhaps because of the higher humidity in the air.