Comparison of dry and wet deposition of particulate matter in near-surface waters during summer.

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 <10 µm) removal. The results showed: Daily concentrations of PM, dry deposition velocities and fluxes changed with the same variation trend. The daily average deposition velocity for PM10 (3.19 ± 1.18 cm·s-1) was almost 10 times that of PM2.5 (0.32 ± 0.33 cm·s-1). For PM2.5, the following dry deposition fluxes were recorded: 10 m (0.170 ± 0.463 µg·m-2·s-1) > 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.