Temporal and spatial distributions of total gaseous mercury concentrations in ambient air in a mountainous area in southwestern China: Implications for industrial and domestic mercury emissions in remote areas in China

Spatial and temporal distributions of total gaseous mercury (TGM) concentrations in ambient air were investigated in the Mt. Gongga area (Sichuan province, PR China) from April 2006 to June 2007. The annual geometric mean TGM concentration at the Moxi baseline station was 3.90 ± 1.20 ng m^− 3. Geometric mean TGM concentrations at 14 representative sampling sites during the warm season ranged from 1.60 to 20.1 ng m^− 3 and varied spatially, with levels decreasing between urbanized areas and more remote regions: urban area (U1-U3: 7.76 ± 4.57 to 20.1 ± 15.1 ng m^− 3), town (T1: 4.61 ± 1.15 ng m^− 3) and village (V1-V4: 3.26 ± 0.63 to 8.45 ± 3.06 ng m^− 3), and remote area (R1-R6: 1.60 ± 0.43 to 3.41 ± 1.26 ng m^− 3). Our study suggested that industrial activities, especially non-ferrous smelting activities, were an important source of atmospheric Hg and played a vital role in the regional distribution of TGM. In addition, domestic coal and biomass combustion to heat residential homes were important sources of TGM in densely populated areas during the winter months.     

The key spatial elements and high-density development of urban peninsula: A discussion on the relationship between core and cape

Urban peninsulas are an important category with distinctive geographical characteristics in the history of human settlements. Despite their time-honored development, abundant cultural accumulation, and developed water transportation, a considerable number of world-famous urban peninsulas demonstrate a remarkable feature of high-density development because of their limited space for expansion. Based on the in-depth analysis of the connotation and features of urban peninsulas, this study summarizes five basic elements concerning the space of urban peninsulas, namely, capes, boundaries, networks, nodes, and cores. On the basis of these five elements, different high-density developmental modes of urban peninsulas are construed to provide a reference model for the location, density control, and urban structure of high-rise building clusters in peninsulas and further reveal the significance and value of high-rise buildings in shaping the special urban form of peninsulas.     

The effect of floor heat source area on the induced airflow in a room

We examine the role of heat source geometry in determining rates of airflow and thermal stratification in natural displacement ventilation flows. We modify existing models to account for heat sources of finite (non-zero) area, such as formed by a sun patch warming the floor of a room. Our model allows for predictions of the steady stratification and ventilation flow rates that develop in a room due to a circular heat source at floor level. We compare our theoretical predictions with predictions for the limiting cases of a point source of heat (yielding a stratified interior), and a uniformly heated floor (yielding a mixed interior). Our theory shows a smooth transition between these two limits, which themselves result in extremes of ventilation, as the ratio of the heat source radius to the room height increases. Our model for the transition from displacement to mixing ventilation is compared to previous work and demonstrates that the transition can occur for smaller sources than previously thought, particularly for rooms with large floor area compared to ceiling height.     

The short-term effect of air pollution on cardiovascular mortality in Tianjin, China: comparison of time series and case-crossover analyses

Background

Many studies have illustrated that ambient air pollution negatively impacts on health. However, little evidence is available for the effects of air pollution on cardiovascular mortality (CVM) in Tianjin, China. Also, no study has examined which strata length for the time-stratified case-crossover analysis gives estimates that most closely match the estimates from time series analysis.

Objectives

The purpose of this study was to estimate the effects of air pollutants on CVM in Tianjin, China, and compare time-stratified case-crossover and time series analyses.

Method

A time-stratified case-crossover and generalized additive model (time series) were applied to examine the impact of air pollution on CVM from 2005 to 2007. Four time-stratified case-crossover analyses were used by varying the stratum length (Calendar month, 28, 21 or 14 days). Jackknifing was used to compare the methods. Residual analysis was used to check whether the models fitted well.

Results

Both case-crossover and time series analyses show that air pollutants (PM₁₀, SO₂ and NO₂) were positively associated with CVM. The estimates from the time-stratified case-crossover varied greatly with changing strata length. The estimates from the time series analyses varied slightly with changing degrees of freedom per year for time. The residuals from the time series analyses had less autocorrelation than those from the case-crossover analyses indicating a better fit.

Conclusion

Air pollution was associated with an increased risk of CVM in Tianjin, China. Time series analyses performed better than the time-stratified case-crossover analyses in terms of residual checking.     

The effect of beaver ponds on the nonpoint source water quality of a stream in Southwestern Wyoming

Currant Creek, a second order stream in southwestern Wyoming, has three large complexes of beaver ponds midway along its 32 km length. To determine whether these ponds improve the quality of water flowing through them, during spring and summer of 1984 and 1985 water samples were taken upstream from, within, and downstream from the pond complexes. During periods of high flow (i.e. spring runoff), concentrations of suspended solids (SS), total phosphorus (TP), sodium hydroxide-extractable phosphorus (NaOH-P, an index of biologically available P) and total Kjeldahl nitrogen (TKN) were reduced in water flowing through the beaver ponds. During low flow, beaver ponds had less effect on these parameters. Concentrations of nitrate nitrogen (NO₃-N) were reduced during both high and low flows, while concentrations of ortho-phosphate (ortho-P) did not appear to be affected by beaver ponds. Ammonia nitrogen almost always was at the limit of detection. Regression of NaOH-P versus [SS plus ortho-P] suggested that the primary source of NaOH-P was SS. In general, SS explained a large portion of the variation in TP, TKN, and NaOH-P, and often ortho-P was significantly correlated to TP. The increase in the concentration of most parameters below the area with dam complexes appears to reflect input from bank and channel erosion, and export of SS, TP, TKN and NO₃-N from beaver dam complexes was calculated to be less than that from stream sections above or below the dams. Thus the location of dams should be considered before using them to try and improve water quality. The apparent importance of bank and channel erosion as the primary source of nutrients to Currant Creek contrasts with many watersheds in agricultural areas.     

The effect of pre-aeration on the purification processes in the long-term performance of a horizontal subsurface flow constructed wetland

Different conditions (water level, oxygen supply) prevailing in both beds of the Kodij?rve double-bed horizontal subsurface flow (HSSF) constructed wetland (CW) (Southern Estonia; constructed in 1996, total area 312.5 m(2), 40 pe) provide the opportunity to compare how different operational methods have altered the efficiency of the purification processes inside the HSSF CW. In summer 2002 a vertical subsurface flow (VSSF) CW (total area 37.4 m(2)) was added as the first stage of the system. Data from 18 sampling wells installed in Kodij?rve HSSF CW from two periods is compared: 1st period -- January 2000-April 2002 (before the VSSF CW was built); 2nd period --October 2002-December 2004 (after the construction of the VSSF filter). The VSSF CW has remarkably improved aerobic conditions in both beds of the HSSF. Apart from total phosphorus concentrations in the right bed and nitrate nitrogen concentrations in the outflow of both beds, all of the water quality indicators (dissolved oxygen, total suspended solids, biological oxygen demand, ammonia nitrogen, nitrite nitrogen, total nitrogen and total iron) improved after the construction of the VSSF filter. Typically, purification processes in the HSSF CW were dependent on oxygen supply, which was partly influenced by the water level inside the filter beds.     

Assessing the mitigation effect of deep tunnels on urban flooding: a case study in Guangzhou,China

ABSTRACT

There are growing demands of deep tunnels to mitigate the severe urban flooding by providing a large storage capacity for excess storm runoff. This study aims to assess the flooding mitigation effect of a deep tunnel system proposed in the old downtown of Guangzhou, China, and to quantify the flooding volume difference by two storm hyetographs, the Chicago curve and the Improved Huff curve. Results show that the flooding volume is significantly reduced by a minimum of 19% and a maximum of 42% under design storms of 10- and 0.5-year return periods, respectively, when the deep tunnel system is constructed. There is a distinct spatial pattern for the mitigation effect. The best mitigation is in the west and the immediate north of the main tunnel, whereas the east does not show significant mitigation. Moreover, the actual flooding risk is likely underestimated when the Chicago curve is employed to design the storms.     

Lidar observations of the diurnal variations in the depth of urban mixing layer: a case study on the air quality deterioration in Taipei, Taiwan

An aerosol light detection and ranging (LIDAR) system was used to measure the depth of the atmospheric mixing layer over Taipei, Taiwan in the spring of 2005. This paper presents the variations of the mixing height and the mixing ratios of air pollutants during an episode of air quality deterioration (March 7-10, 2005), when Taipei was under an anti-cyclonic outflow of a traveling high-pressure system. It was found that, during those days, the urban mixing height reached its daily maximum of 1.0-1.5 km around noon and declined to 0.3-0.5 km around 18:00 (LST). In terms of hourly averages, the mixing height increased with the ambient temperature linearly by a slope of 166 m/degrees C in daytime. The consistency between the changes in the mixing height and in the ambient temperature implied that the mixing layer dynamics were dominated by solar thermal forcing. As the cap of the mixing layer descended substantially in the afternoon, reduced dispersion in the shallow mixing layer caused the concentrations of primary air pollutants to increase sharply. Consequently, the pollutant concentration exhibited an anti-correlation with the mixing height. While attentions are usually focused on the pollution problems occurring in a morning inversion layer, the results of this study indicate that the air pollution and its health impacts could be even more severe as the mixing layer is getting shallow in the afternoon.     

The cooling effect of green spaces as a contribution to the mitigation of urban heat: A case study in Lisbon

Green areas in the urban environment can contribute to the mitigation of the Urban Heat Island. In a context of climate change, with the expected increase in temperature, dryness and intensity of heat waves, green areas assume even higher importance as they can create a cooling effect that extends to the surrounding areas. This study analyses the thermal performance of a small green space (0.24 ha) and its influence in the surrounding atmospheric environment of a densely urbanised area in Lisbon. Measurements of weather parameters (temperature, relative humidity, wind speed, solar and infrared radiation) were carried out along a selected path, starting from inside the green area to surrounding streets with different orientations and solar exposure. It was found that the garden was cooler than the surrounding areas, either in the sun or in the shade. These differences were higher in hotter days and particularly related to the mean radiant temperature (Tmrt). The highest difference found was of 6.9 °C in relation to air temperature and 39.2 °C in relation to Tmrt; in both cases this difference occurred between the shaded site inside the garden and the sunny site in an E–W oriented street in the southern part of the studied area. Besides the local weather conditions, particularly the low wind speed, the sun exposure and the urban geometry are the potential factors that explain these differences. The cooling effect of green areas on the surrounding environment can be enhanced by additional measures related to the urban features of each city.     

Impact of source waters,disinfectants, seasons and treatment approaches on trihalomethanes in drinking water: a comparison based on the size of municipal systems

This study compares concentrations of trihalomethanes (THMs) in municipal water for 2001–2007 from the small and large systems in two provinces in Canada (Newfoundland and Quebec) based on source waters, disinfectants, seasons and treatment approaches. Approximately 71 and 94%, respectively, of the municipal systems in Quebec and Newfoundland are small systems (serving fewer than 3000 people). The small systems serve approximately 8.6% (0.57 million) and 44.1% (0.18 million) of the populations in Quebec and Newfoundland, respectively. Concentrations of THMs and its variability are much higher in the small systems (Quebec: 0–941 μg/L; Newfoundland: 0–875 μg/L) than in the systems with populations 10 000 or more (Quebec: 0–364 μg/L; Newfoundland: 2.3–205 μg/L). The study reveals that the differences in THMs between the small and medium/large systems are because of different types of source waters, treatments, disinfection strategies and seasons. The results emphasize that regulatory agencies must focus more on the occurrence of DBPs in small systems and identify strategies to reduce their levels in drinking water.     

Changes in the total costs of the English and Welsh water and sewerage industry: The decomposed effect of price and quantity inputs on efficiency

Understanding what drives changes in regulated water companies' costs is of great relevance to water regulators. This study decomposes and estimates the change in total costs for a sample of ten water and sewerage companies in England and Wales from 1993 to 2016. The results demonstrate that companies' total costs increased over time due to increases in input prices and input quantity. Any gains obtained from the efficient allocation of resources and technical progress were lost due to mergers and technical inefficiency. Finally, we link our results with the regulatory cycle to evaluate the impact of the regulatory regime on companies' costs and discuss some policy implications.     

Investigation of the relationship between place characteristics and child behavior in residential landscape spaces: a case study on the Century Sunshine Garden Residential Quarter in Hefei

This paper reviewed child behavior in Chinese residential landscapes. A field survey was used to investigate place characteristics, whereas fixed-point observation and visualization records were utilized to analyze child behavior. Children were then classified into two categories, namely, those with action capacity and those with little capacity. Based on the classification and comparative analysis of place characteristics, along with the quantitative and visualized analysis of child behavior, the relationship between these two aspects was determined, and the effect of spatial elements in the selected residential areas on such a relationship was clarified. Additionally, the designing of a comprehensive landscape space that satisfies children's needs was also discussed. The conclusions are as follows: (1) Waterside is the element that most significantly affects child behavior. Children who can act on their own prefer to play along the waterside. (2) Open spaces attract children with action capacity, whereas children with little capacity tend to choose more private spaces. (3) Despite the presence of facilities for various activities, an extremely open space or one that is separated by a road still affects child behavior. (4) A comprehensive space with a water landscape, fitness facilities, high accessibility, and a number of cultural events may significantly affect child behavior. Both types of children were found to enjoy a place with such characteristics. Therefore, the evaluation of residential landscape space should be integrated with landscape design.