Zhenming Zhang

Spatiotemporal Characteristics of Particulate Matter and Dry Deposition Flux in the Cuihu Wetland of Beijing

In recent years, the rapid development of industrialization and urbanization has caused serious environmental pollution, especially particulate pollution. As the “Earth’s kidneys,” wetland plays a significant role in improving the environmental quality and adjusting the climate. To study how wetlands work in this aspect, from the early autumn of 2014 to 2015, we implemented a study to measure the PM concentration and chemical composition at three heights (1.5, 6, and 10 m) during different periods (dry, normal water, and wet periods) in the Cuihu wetland park in Beijing for analyzing the dry deposition flux and the effect of meteorological factors on the concentration. Results indicated that (1) the diurnal variations of the PM2.5 and PM10 concentrations at the three heights were similar in that the highest concentration occurred at night and the lowest occurred at noon, and the daytime concentration was lower than that at night; (2) the PM2.5 and PM10 concentrations also varied between different periods that wet period > normal water period > wet period, and the concentration at different heights during different periods varied. In general, the lowest concentration occurred at 10 m during the dry and normal water periods, and the highest concentration occurred at 1.5 m during the wet period. (3) SO42−, NO3−, and Cl− are the dominant constituents of PM2.5, accounting for 42.22, 12.6, and 21.56%, respectively; (4) the dry depositions of PM2.5 and PM10 at 10 m were higher than those at 6 m, and the deposition during the dry period was higher than those during the wet and normal water periods. In addition, the deposition during the night-time was higher than that during the daytime. Moreover, meteorological factors affected the deposition, the temperature and wind speed being negatively correlated with the deposition flux and the humidity being positively correlated. (5) The PM10 and PM2.5 concentrations were influenced by meteorological factors. The PM2.5 and PM10 concentrations were negatively correlated with temperature and wind speed but positively correlated with relative humidity.

Multi-scale comparison of the fine particle removal capacity of urban forests and wetlands

As fine particle (FP) pollution is harmful to humans, previous studies have focused on the mechanisms of FP removal by forests. The current study aims to compare the FP removal capacities of urban forests and wetlands on the leaf, canopy, and landscape scales. Water washing and scanning electron microscopy are used to calculate particle accumulation on leaves, and models are used to estimate vegetation collection, sedimentation, and dry deposition. Results showed that, on the leaf scale, forest species are able to accumulate more FP on their leaf surface than aquatic species in wetlands. On the canopy scale, horizontal vegetation collection is the major process involved in FP removal, and the contribution of vertical sedimentation/emission can be ignored. Coniferous tree species also showed stronger FP collection ability than broadleaf species. In the landscape scale, deposition on the forest occurs to a greater extent than that on wetlands, and dry deposition is the major process of FP removal on rain-free days. In conclusion, when planning an urban green system, planting an urban forest should be the first option for FP mitigation.

Impacts of aquatic macrophytes configuration modes on water quality

Constructed wetland technology is regarded as an important ecological restoration technology and used widely in sewage disposal. In order to give them a wider scope of application and to improve their performance in water restoration, the current experiment was designed. Four aquatic macrophytes (dwarf cattail (TM), yellow-flowered iris (WI), water shallot (ST) and watermifoil (MS)) were picked and planted in artificial floating islands (AFIs) in different configurations (TM + WI, ST + MS and TM + WI + MS) and two patterns, radiation pattern (RP) and annular pattern (AP), for a 60-day experiment. Then, water quality and growth were monitored every 10 days. The results indicate that the different configurations performed diversely on waste water purification. First, a composite plant configuration removed more pollutant than a single one with the same total increment of biomass. Second, the plant configuration of MS + ST was most effective in total nitrogen (TN), total phosphorus (TP) or PO4(3-) removal, and TM + IW + MS was good at chemical oxygen demand (COD) and NO3(-) removal. However, different patterns comprised from the same species had a certain effect on absorption of pollutants. Generally speaking, plant configurations with a RP were better than an AP in purification. Accordingly, these provided the methods for the pollution wetland restoration.

Sabina chinensis and Liriodendron chinense improve air quality in Beijing, China

Urban forests have been shown to be efficient for reducing air pollutants especially for particulate matters (PMs). This study aims to reveal the PM blocking capacity of two common artificial landscape species, Sabina chinensis and Liriodendron chinense and to investigate spatial-temporal heterogeneities by estimating the vegetation collection velocity of coarse (PM10) and fine particles (PM2.5) during different seasons and heights. PM concentration and meteorological data were collected on both leeward and windward sides of trees during the daytime in both summers and winters from 2013 to 2015. Concentration and meteorological monitors were installed at three heights, bottom (1.5 m), middle (3.5 m), and top (5.5 m) of the canopy. The results showed: During daytime, the collection velocity changed and PM2.5 collection velocity was much higher than that of PM10. Furthermore, the maximum collection velocities of L. chinense and S. chinensis occurred at 14:00–16:00 both in summer and winter. Moreover, the collection velocity had a positive correlation with wind speed and temperature. The blocking capacities of L. chinense and S. chinensis varied from season to season, and the concentrations of particulate matter indicate the middle canopy of both species as the most effective part for TSP blocking. Furthermore, these two species are more effective blocking in PM2.5 than PM10. The blocking capacity of S. chinensis is generally better. The vegetation collection is the major process of PM removal near the ground and sedimentation was not taken into consideration near the ground.

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.

Effect of the wetland environment on particulate matter and dry deposition

ABSTRACT In Beijing, particulate matter (PM) in the atmosphere, especially PM2.5 and PM10, 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 PM2.5 and PM10 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. GRAPHICAL ABSTRACT

Do Aquatic Macrophytes Configuration Mode Impact Water Quality

This paper had selected watermifoil (Myriophyllum veticillatum Linn.), softstem bulrush (Scirpus validus Vahl) and yellow-flowered iris (Iris wilsonii), in showing the water purification through different configuration. AFIs with different combination of aquatic plants were set up to purify the water quality for 50 days. This paper aimed to evaluate chemical and vegetative characteristics of each type of plant and also to find configuration of aquatic plants to maximize the contaminants removal efficiency by artificial floating island (AFI). The result indicated that the trophic waterbody promote the growth of plants and all of the AFIs have the ability to purify water and reduce contaminants. However, the most effective way is by combination of these three aquatic plants which has strong capacity to remove COD, NO3-, total nitrogen, total phosphorous and improve pH levels. Watermifoil (Myriophyllum verticillatum Linn.) is better than yellow-flowered iris (Iris wilsonii) and softstem bulrush (Scirpus validus Vahl) in disposing water pollutants.

Potential of aquatic macrophytes and artificial floating island for removing contaminants

Eutrophication is a major environmental issue that mankind is facing today as a result of rapid development. To reduce the eutrophication problem, we are testing an innovative artificial floating islands (AFIs) approach. AFIs include aquatic plants composed of emergent and floating macrophytes. In this experimental approach, two aquatic plants were selected to compare with the control group in order to evaluate the capacity of AFIs. These two emergent macrophytes were evaluated for a 40-day timeframe to examine their ability to purify waste water. The results showed that an AFI with purple loosestrife (Lythrum salicaria Linn.) and one with yellow-flowered iris (Iris wilsonii) have a strong ability to remove nitrogen, phosphorus, and other pollutants from water bodies. The pollutant removal rates of the AFIs with purple loosestrife and yellow-flowered iris were almost over 50%. The chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal rates of the AFI with purple loosestrife were about 75%, 57%, 71%, respectively. At the same time, the COD, TN, and TP removal rates of the AFI with yellow-flowered iris were 60%, 49%, and 68%, respectively. AFIs with aeration are also a good way to remove pollutants. This study reveals that AFIs can be incorporated into wetlands to reduce the effects of water contamination and help strengthen wetland restoration.