Effect of the wetland environment on particulate matter and dry deposition

Abstract

In Beijing, particulate matter (PM) in the atmosphere, especially PM and PM, have attracted public attention because of its adverse effects. A series of studies have investigated the sources and spatial-temporal variation of PM. Wetland has been reported to own the capacity of resolving air problem. To examine the characteristics of the particulate matter in wetlands, the diurnal variation of PM and PM concentrations with respect to two heights (i.e. 1.5 and 10 m, respectively) and three meteorological factors (i.e. wind speed, temperature, and relative humidity, respectively) was monitored in the Cuihu National Wetland Park in Beijing, and the dry deposition velocity and flux were analysed using the above-mentioned data. Results indicated that (1) As for diurnal variation, the PM concentration constantly decreased at 07:00-16:00 and gradually increased at 16:00-18:00. The maximum instantaneous concentration was observed at 07:00-10:00, while the minimum instantaneous concentration was observed at 13:00-16:00. (2) The annual concentration variation of PM followed the order of dry period > wet period > normal period. (3) The particulate concentrations at 10 m were always greater than those at 1.5 m. (4) The PM concentration was positively correlated to the relative humidity and negatively correlated to the temperature. Wind speed exhibited a complex effect on PM concentration. (5) The regulation of dry deposition efficiency followed the order of spring > winter > summer. (6) Wind speed strongly and positively affected the dry deposition velocity of PM10. The effects of temperature and relative humidity on dry deposition were uncertain.

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.…”

“…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]. Inversely, Yang et al showed the influences of temperature and relative humidity on dry deposition were uncertain [61].…”

“…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]. Inversely, Yang et al showed the influences of temperature and relative humidity on dry deposition were uncertain [61]. In this study, the wind speed in winter and spring on the wetland was higher than that in summer and autumn, which is in contrast to the circumstance on the bare land, where the wind speed in summer and autumn exceeded that in the other two seasons, as shown in Table 1.…”

“…In previous studies the removal efficiency [23,58] was calculated by the ratio of dry deposition flux (μg•m -2 •s -1 ) and concentration (g•m -3 ), According to Equation (1), the removal effects depend on the dry deposition and the mass particles' average concentration [11,28,29]. The dry deposition of particles near the ground is more sensitive to meteorological variations and human activities [61]. 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 dry deposition of particles near the ground is more sensitive to meteorological variations and human activities [61]. 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].…”