Atmospheric particulate matter (PM) deposition which involves both dry and wet processes is an important means of controlling air pollution. To investigate the characteristics of dry and wet deposition in wetlands, PM concentrations and meteorological conditions were monitored during summer at heights of 1.5 m, 6 m and 10 m above ground level at Cuihu Wetland (Beijing, China) in order to assess the efficiency of PM2.5 (particles with an aerodynamic size of <2.5 μm) and PM10 (particles with an aerodynamic size of 6 m (0.007 ± 0.003 μg·m^–2·s^–1) > 1.5 m (0.005 ± 0.002 μg·m^–2·s^–1). And the following deposition fluxes for PM10 were recorded: 10 m (2.163 ± 2.941 μg·m^–2·s^–1) > 1.5 m (1.565 ± 0.872 μg·m^–2·s^–1) > 6 m (0.987 ± 0.595 μg·m^–2·s^–1). In the case of wet deposition, the relative deposition fluxes for PM2.5 and PM10 were 1.5 m > 10 m > 6 m, i.e. there was very little difference between the fluxes for PM2.5 (0.688 ± 0.069 μg·m^–2·s^–1) and for PM10 (0.904 ± 0.103 μg·m^–2·s^–1). It was also noted that rainfall intensity and PM diameter influenced wet deposition efficiency. Dry deposition (63%) was more tilted towards removing PM10 than was the case for wet deposition (37%). In terms of PM2.5 removal, wet deposition (92%) was found to be more efficient.

The Plain Forestation Project is an important measure designed to alleviate air pollution in Beijing, the capital of China. Ten commonly cultivated forest types of the Plain Forestation Project were studied at three growth stages of leaves. The particulate matter (PM)_2.5 concentrations and forest structures were surveyed to analyze the PM_2.5 concentration differences between different forest types, and establish a linear relationship between forest structures and PM_2.5 concentration differences. The results suggested that forest ecosystems can block and capture PM_2.5 from the air. Forests with luxuriant foliage are most effective in removing PM_2.5 from the air. The average PM_2.5 mass concentration in the Leaf-on Period (LOP) was the lowest when compared with other periods. The PM_2.5 concentrations in the forest usually were higher than the control. Correspondingly, PM_2.5 concentration indexes were negative values during daytime, but this results were reversed at night. Forests can reduce the diffusion rate of PM_2.5 leading to PM_2.5 were detained in the forest during daytime, and play an important role in the adsorption or deposition of particulate matter at night. Forest structure was primary reason of the PM_2.5 concentration difference between different forests. The PM_2.5 concentration index was positively correlated to canopy density, leaf area index (LAI), and mean diameter at breast height (DBH), and negatively correlated to the average tree height (height), forestland area, grass coverage and height.

Structural hydrological connectivity has been proposed to describe the geological structure of the landscape as well as to explain hydrological behaviors. Indices based on the topological or soil condition were developed to interpret their relationships. While previous studies mainly focused on well-instrumented catchments which are narrow in humidity or temperate zone, the hydrological responses to structural connectivity at the plot and hill slope scale as well as in arid or semi-arid climate conditions remain unclear. This study was conducted in the semi-arid mountainous region of northern China in Haihe Basin which is the source of water of about 350 million people. Experiments were conducted during the rainy season in 2012 and 2013 using four runoff plots. Two indices, flow path length (FL) based on topography and integral connectivity scale length (ICSL) based on soil moisture conditions, developed to represent hydrological connectivity structure and the runoff response to rainfall were analyzed. The results showed that the surface runoff coefficient was strongly and positively linearly correlated to FL, and the correlation between subsurface flow and ICSLs was quadratic. Plots with shorter FL required more rainfall to generate surface runoff. In the shallow soil layer, when the ICSLs are relatively low, the soil can store more water and less rainfall feeds subsurface runoff. Further analysis indicated that improved shallow soil connectivity conditions might enhance the water-holding capacity and lead to lower water yields for each event. This study demonstrated that hydrological structure connectivity could explain the mechanism of runoff generation in semi-arid areas while further experiments should be undertaken to find the threshold-like relationship between FL and surface runoff as well as the influence of plant cover on hydrological behaviors.