Particle removal by vegetation: comparison in a forest and a wetland

Abstract

Vegetation collection is one of the most effective scavenging methods but relevant studies are limited. It can be described by some abstract parameters such as collection rates and deposition fluxes within the canopy. In order to estimate the dry deposition within the canopy of particular matters (PMs) in Beijing, a highly particle-polluted city, and reveal the PM pollution-removal abilities of plants in wetlands and forests, concentration and meteorological data were collected during the daytime in an artificial forest and a wetland in the Olympic Park in Beijing. The dry depositions within the canopy and vegetation collection rates were calculated by a well-developed model and validated by measured deposition fluxes in 11 random experiment days. The experiment year was divided into three plant growth stages based on canopy density, and the day was divided into four different times. Two heights, 10 and 1.5 m, were defined in the forest while in the wetland, 0.5 and 1.5 m were defined. The results showed that in Beijing, the most severe pollution by PMs occurs in the non-leaf stage (NS), and the full-leaf stage (FS) is the cleanest stage. In NS, namely winter, more fossil fuel was used for worms in Beijing and peripheral areas and this might be the reason for the serious pollution condition. Within the canopy, PM deposition fluxes in the wetland are more than those in the forest, but the vegetation collection rates of the forest are higher. The lower temperature conditions led to more dry deposition, and the larger canopy contributed to the higher collection rates. During the daytime, over the year, the deposition of PM in three plant growth stages is NS ≥ half-leaf stages (HS) ≥ FS, whereas the deposition of PM is NS ≥ FS ≥ HS, and during the daytime, the maximum deposition fluxes occur in 6:00-9:00 in the wetland while the minimum deposition values occur in 15:00-18:00. This phenomenon was related to the temporal variation of particle concentration.

Seasonal Variations and Chemical Characteristics of PM2.5 Aerosol in the Urban Green Belt of Beijing, China

“…Recently more and more studies focused on the effect of forests in particle removal [13]. Research in Beijing Olympic Forest Park showed PM 2.5 concentration within the forest to be approximately 1.5 times greater than outside, which indicates that the forest may block the pollutants in it [14].…”

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

“…The deposition velocity is determined by both the atmosphere conditions and the roughness of different land covers, and wetlands and bare lands have similar roughness [35]. In previous studies, parameterized roughness coefficients of these two land covers are estimated to be the same [23,45]. Besides, the empirical model was developed and verified in Beijing where our research was conducted and thus the calculated results are reliable.…”

“…The structure of this model is relatively simple, and the data required are easy to collect compared with the physical process-based model [35]. Previous studies in Beijing estimated this model and found that the results based on the model were considered to be credible [34,45]. However, uncertainties of this study should be also highlighted here.…”

“…This was due to the weather conditions with cloud and thundershowers on the two days, and as a result, the relative humidity on the wetland was higher at night, which was beneficial for the accumulation of coarse particulate matter, while during the daytime, it decreased with the increase of temperature. In addition, it is estimated that the plants grown in the wetland and the waters could capture, absorb, and dissolve the particulates, particularly the fine particles [45]. Li [27] compared the capturing and dissolving capacity of seven different plants including Phragmites australis, Typha angustifolia, Scirpus tabernaemontani, Iris tectorum, Zizania aquatica, Eichhornia crassipes, and Sagittaria sagittifolia grown in wetlands, and calculated the amounts of particles captured and absorbed by the plants.…”

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