During this study 158 whole air samples were collected in 45 Chinese cities in January and February 2001. The spatial distribution of different classes of halocarbons in the Chinese urban atmosphere, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), Halon-1211, and other chlorinated compounds is presented and discussed. Most of these compounds were enhanced compared to background levels. However, the mean enhancement of CFCs was relatively small, with CFC-12 and CFC-11 increases of 6% (range 1–31%) and 10% (range 2–89%), respectively, with respect to the global background. On the contrary, strongly enhanced levels of CFC replacement compounds and halogenated compounds used as solvents were measured. The average Halon-1211 concentration exceeded the background of 4.3 pptv by 75% and was higher than 10 pptv in several cities. Methyl chloride mixing ratios were also strongly elevated (78% higher than background levels), which is likely related to the widespread use of coal and biofuel in China. 相似文献
An ecological study was conducted on two landfill sites in Hong Kong. Both sites were contaminated by landfill gas and leachate, as indicated by the high concentrations of CH(4) and CO(2) and the presence of high concentration of NH(4)-N in the cover soil layer. Their plant diversity and performance, as well as the soil and litter animals, were compared with three derelict sites as references. The landfill sites had higher plant coverage and plant diversity, and higher densities of soil and litter animals than the reference sites. Similarly, the microbial activities at the landfill sites were higher than those at reference sites. The results showed that the landfill sites possessed an effective food web, starting from microbes to macroinvertebrates. Woodland establishment seems feasible at these landfill sites, and natural succession appears to take place at a higher rate at these landfill sites when compared with the reference sites. 相似文献
The Narim gold mine is located approximately 200km southeast of Seoul within the Sulcheon mineralised district in the Yeongnam massif, Korea. In this study, environmental geochemical analyses were undertaken for soil, sediment and water samples collected in April, September and November in 1998 from the Narim mine creek. The mine area consists mainly of granitic gneiss; however, mineral constituents of soil and sediment near the mine were mainly composed of quartz, feldspar, mica, amphibole, some pyrite and clay minerals. Also were found some pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, malachite, goethite, various hydroxide and unidentified secondary minerals. Generally, high concentrations of heavy metals in the soil and sediment are correlated with a high proportion of secondary minerals. Hydrochemical compositions of water samples are characterised by relative significant enrichment of Na++K+ and alkali metals in the ground water, whereas the surface and mine waters are relatively enriched in Ca2++Mg2+ and heavy metals. Anion contents of the ground waters are typically enriched in HCO3–, NO3– and Cl–, whereas the surface and mine waters are highly enriched in HCO3– and SO42–. The pH and EC values of the surface water from the non-mine creek are relatively lower compared with those of the surface water around the mine and waste dump. The range of D and 18O values (d parameters) of the water samples are shown in distinct two groups for the April waters of 10.1–13.1, and for the November waters of 5.8–7.9, respectively. This range variation indicates that two group water were composed of distinct waters because of seasonal difference. Geochemical modelling showed that mostly heavy toxic metals may exist largely in the form of free metal (M2+) and metal-sulphate (MSO42–), and SO42– concentration influenced the speciation of heavy metals in the mine water. These metals in the ground water could be formed of CO3– and OH– complex ions. Using a computer program, saturation indices of albite, calcite, dolomite in mostly surface water show undersaturated and progressively evolved toward the saturation state, however, ground and mine waters are nearly saturated. The gibbsite, kaolinite and smectite are supersaturated in the surface and ground water, respectively. Calculated water-mineral reaction and stabilities suggest that the weathering of silicate minerals may be stable kaolinite. The clay minerals of K-illite and Na-smectite will be transformed to more stable kaolinite owing to the continuous reaction. 相似文献
Objective: Electric bikes (e-bikes) have been one of the fastest growing trip modes in Southeast Asia over the past 2 decades. The increasing popularity of e-bikes raised some safety concerns regarding urban transport systems. The primary objective of this study was to identify whether and how the generalized linear regression model (GLM) could be used to relate cyclists' safety with various contributing factors when riding in a mid-block bike lane. The types of 2-wheeled vehicles in the study included bicycle-style electric bicycles (BSEBs), scooter-style electric bicycles (SSEBs), and regular bicycles (RBs).
Methods: Traffic conflict technology was applied as a surrogate measure to evaluate the safety of 2-wheeled vehicles. The safety performance model was developed by adopting a generalized linear regression model for relating the frequency of rear-end conflicts between e-bikes and regular bikes to the operating speeds of BSEBs, SSEBs, and RBs in mid-block bike lanes.
Results: The frequency of rear-end conflicts between e-bikes and bikes increased with an increase in the operating speeds of e-bikes and the volume of e-bikes and bikes and decreased with an increase in the width of bike lanes. The large speed difference between e-bikes and bikes increased the frequency of rear-end conflicts between e-bikes and bikes in mid-block bike lanes. A 1% increase in the average operating speed of e-bikes would increase the expected number of rear-end conflicts between e-bikes and bikes by 1.48%. A 1% increase in the speed difference between e-bikes and bikes would increase the expected number of rear-end conflicts between e-bikes/bikes by 0.16%.
Conclusions: The conflict frequency in mid-block bike lanes can be modeled using generalized linear regression models. The factors that significantly affected the frequency of rear-end conflicts included the operating speeds of e-bikes, the speed difference between e-bikes and regular bikes, the volume of e-bikes, the volume of bikes, and the width of bike lanes. The safety performance model can help better understand the causes of crash occurrences in mid-block bike lanes. 相似文献
Particle density is an important physical property of atmospheric particles.The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles.In the present study,a centrifugal particle mass analyzer(CPMA) combined with a differential mobility analyzer(DMA) was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016.The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm~3,on average.The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm~3 for 50 to350 nm particles.Extra modes with peaks at 1.0,0.8,and 0.6 g/cm3 for 150,240,and 350 nm particles,which might be freshly emitted soot particles,were observed during intensive primary emissions episodes.The particle effective densities showed a diurnal variation pattern,with higher values during daytime.A case study showed that the effective density of Aitken mode particles during the new particle formation(NPF) event decreased considerably,indicating the significant contribution of organics to new particle growth. 相似文献
ABSTRACT: Ground water flow and supply at the Whiteshell Research Area (WRA) in southeastern Manitoba and the advective movement of contaminants from a hypothetical nuclear fuel waste disposal vault to the adjacent biosphere and a nearby ground water supply well are simulated using finite-element modeling and numerical particle-tracking technique. The hypothetical vault is located at a depth of 500 m, below the water table, in low-permeability plutonic rock of the Canadian Shield. The rock mass is intersected by high-permeability fracture zones (aquifers), which also act as conduits for vault contaminants to migrate to the ground surface. The ground water resource is, therefore, limited in quantity and quality and should be explored with care. A 30 m deep well, which pumps water at a rate of 120 m3/yr from a low-dipping fracture zone, LD1, reduces natural discharge from the system to augment natural recharge. At this pumping rate, a 100 m or 200 m deep well neither reduces discharge nor induces recharge into the system. Thus, at the WRA, a 30 m deep domestic water supply well best meets the water requirements of a one-person household at the rate of 120 m3/yr. The 100 m and 200 m wells best meet the requirements of a family of six and a family of six with light irrigation, respectively, without capturing contaminants’pathways from the vault to the ground surface. By virtue of the proximity of the 200 m well intake to the hypothetical vault, this well performs best as a purge well at pumping rates of 0,000 m3/yr and greater. Finite-element modeling is useful in evaluating the water supply potential of a fractured rock environment in which a nuclear waste disposal vault is proposed to be sited. 相似文献
The effects of the water-soluble fraction of dead leaves of the eelgrass Zostera marina L. on the growth of 8 species of micro-algae (pennate and centric diatoms, dinoflagellates, and a green flagellate) and a bacterium were studied on agar plates and in liquid culture. The extracts of leaves which had been dead from a few days to 2 wk inhibited growth and often killed cells in all test organisms. Extracts were lethal even at concentrations equivalent to as little as 0.25 mg dry leaf ml-1, but inhibition decreased when extracts were prepared from leaves aged in the laboratory for 35 d (loss of anti-bacterial activity) or 90 d (loss of anti-algal activity). Extracts of leaves which had aged and dried several months in the field had no effect, except at very high concentrations (13 mg dry leaf ml-1) when the lag phase of growth was prolonged several days in a culture of the chlorophyte Platymonas sp. The active fraction in eelgrass leaves may be important in controlling initial growth of micro-organisms on eelgrass detritus, and it could determine the composition and activity of the epiphytic community on living leaves. 相似文献
In a previous study on the kuruma shrimp Penaeus japonicus from the South China Sea, we detected high genetic divergence between two morphologically similar varieties (I and II) with
distinct color banding patterns on the carapace, indicating the occurrence of cryptic species. In the present study, we clarify
the geographical distribution of the two varieties in the western Pacific by investigating the genetic differentiation of
the shrimp from ten localities. Two Mediterranean populations are also included for comparison. Based on the mitochondrial
DNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises
populations from Japan and China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam,
Singapore and the Philippines), Australia and the Mediterranean. Population differentiation is evident in variety II, as supported
by restriction profiles of two mitochondrial markers and analysis of two microsatellite loci. The Australian population is
genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship.
Variety I does not occur in these three localities, while a small proportion of variety II is found along the northern coast
of the South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high
genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean,
are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery
management and aquaculture development programs of this important biological resource. 相似文献