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

Abstract

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.

The Concentrations and Removal Effects of PM10 and PM2.5 on a Wetland in Beijing

“…By contrast, in summer and autumn, the dry removal efficiencies of PM 10 and PM 2.5 during the night were significantly higher than those during the daytime; in addition, they were higher on the bare land and lower on the wetland. Although there was no significant difference between the dry removal efficiencies of PM 10 and PM 2.5 , on the whole, the dry removal efficiency of PM 10 was greater than that of PM 2.5 , which did conform with the results of Wu et al and Yang et al [60,61]. On the wetland, the dry removal efficiency of PM 10 followed the order of spring > winter > autumn > summer, similar to that of PM 2.5 , which was consistent with the results of Yang et al [61], whereas PM 10 and PM 2.5 dry removal efficiencies on the bare land ranked as autumn > summer > winter > spring.…”

“…However, there was an exception during the night in winter, where the dry removal efficiencies of PM 10 and PM 2.5 on the wetland were lower than those on the bare land. This was because the higher concentrations of PM 10 and PM 2.5 on the bare land led to higher dry deposition and, accordingly, the dry removal efficiencies increased [60]. Surprisingly, we found the dry removal efficiencies of PM 10 and PM 2.5 in summer were lower than those in other seasons.…”

“…temperature, relative humidity, and irradiance [60,63]. There was a negative relationship between the temperature and dry deposition of PM10 and PM2.5: with the decrease of the temperature, the dry deposition increased, whereas the relative humidity had a positive effect on the dry deposition [23,45].…”

“…In addition, it tends to be affected by the deposition velocity, which has a close positive relationship with the wind speed [61][62][63]. The removal effects were also influenced by anthropogenic and other meteorological factors, such as the temperature, relative humidity, and irradiance [60,63]. There was a negative relationship between the temperature and dry deposition of PM 10 and PM 2.5 : with the decrease of the temperature, the dry deposition increased, whereas the relative humidity had a positive effect on the dry deposition [23,45].…”

The Concentrations and Removal Efficiency of PM₁₀ and PM_2.5 on Wetland in Beijing

“…By contrast, in summer and autumn, the removal efficiencies of PM10 and PM2.5 during night were significantly higher than that during daytime, in addition, they were higher on the bare land and lower on the wetland. Although there was no significant difference between the removal efficiencies of PM10 and PM2.5, on the whole, the removal efficiency of PM10 was greater than that of PM2.5, which did conform with the results of Wu et al and Yang et al [50,51]. On the wetland, the removal efficiency of PM10 followed the order of spring > winter > autumn > summer, similar to that of PM2.5, which was consistent with result of Yang et al [51], whereas PM10 and PM2.5 removal efficiencies on the bare land ranked as autumn > summer > winter > spring.…”