中国城市环境中空气负离子研究进展

空气负离子被誉为“空气维生素和生长素”,其浓度被列为衡量空气质量好坏的一个重要指标,对于城市空气质量的改善意义重大。综述了中国城市环境空气负离子研究方面的主要进展,对空气离子产生的机理机制、观测方法、时空特征、评价指标体系以及关键影响因子及其相互之间的关系等方面进行深入和系统的阐述。其中重点阐述了空气负离子与不同自然环境和建筑环境的关系。国内外主要研究结果表明,(1)不同环境场所下空气负离子浓度差别很大,呈现出由城市中心到郊区再到乡村逐渐增大的趋势。(2)空气负离子浓度的年变化和日变化均存在明显差异。(3)水体对空气负离子浓度影响较大,动态水的空气负离子浓度大于静态水,以瀑布为最大。同时离水体的距离越近,周边的空气负离子浓度越高。(4)空气负离子与风的关系最为密切,有风时空气负离子浓度高于无风时,且风速与空气中负离子浓度成正相关。其他因素如温湿度、天气状况、植物绿化、建筑材料以及建筑高度等都能影响空气负离子浓度的高低,从而影响城市环境的空气清新度,其中有研究者发现空气负离子能够降低空气中颗粒物的浓度,并与PM2.5的关系最大。这些研究为综合地指导和评价城市环境空气质量提供科学依据和设计思路。因此笔者结合中国城市化的进程,进一步提出了更多的想法：(1)在控制性详细规划的层面上,与城市设计和城市绿地系统等研究结合起来,开展周期性的空气负离子浓度实证研究。(2)尝试建立空气负离子浓度与城市住区通风关系的评估方法,为城市住区空气清新度与通风关系的评估做应用性基础研究。     

一体式短程硝化-厌氧氨氧化工艺启动过程的亚硝酸盐调控

以两类中试反应器(SBR,116.6 m³,活性污泥法和SBBR,64.8 m³,泥膜法)为对象,接种猪场废水处理厂的活性污泥,通过控制DO、曝气方式为主和外加Na NO₂为辅的亚硝酸盐调控策略,考察不同反应器在启动一体式短程硝化-厌氧氨氧化(combined partial nitritation and ANAMMOX,CPNA)工艺过程中NO₂^--N浓度对ANAMMOX菌的影响.结果表明,在相同运行条件下,泥膜共生的SBBR更适于短程硝化的快速启动.尽管受到NO₂^--N抑制(100～129 mg·L^-1,共计7 d),但SBR在第39 d成功启动了ANAMMOX工艺,其TNRR和TNRE分别为0.069 kg·(m³·d)^-1和23.3%,而长达17 d的NO₂^--N抑制(129～286mg·L^-1...     

Firms' and states’ responses to laxer environmental standards

On June 1, 2017, President Trump announced the United States' withdrawal from the Paris agreement on climate change. Despite this decision, American firms continued investing in low-carbon technologies and some states committed to tougher environmental standards. To understand this apparent paradox, this paper studies how a weakening of environmental standards affects the behavior of profit-maximizing firms. It finds that a relaxation of emission standards (i) may increase firms’ incentives to adopt clean technologies, but not to pollute less; (ii) may negatively affect industry profitability if it is perceived as temporary; and, when this is the case, (iii) the unilateral adoption of stricter standards by large states may increase the expected profitability of every firm.     

Optimization of dilution ventilation layout design in confined environments using Computational Fluid Dynamics (CFD)

Dilution ventilation systems have been widely used to control the airborne toxic and explosive material in confined spaces. Layout design of dilution ventilation is critical to industrial hygiene control and ventilation efficiency. A properly designed dilution ventilation system can significantly improve the safety of confined workshops and maintain a comfortable work condition. In this work, Computational Fluid Dynamics (CFD) has been used to analyze the performance of dilution ventilation system in the confined workshop environment. Seven different ventilation layouts are proposed to evaluate ventilation performance of different installation layouts. Carbon monoxide (CO), which has the similar density as air, is selected as the sample contaminant to conduct steady-state CFD simulations. The simulation results of different layouts are examined and compared to get the optimal layout design for the best contaminant control. Results have shown that the layout with two opposite inlets has the highest ventilation efficiency among seven proposed layouts. This work can serve as a reference to increase dilution ventilation efficiency and minimize the energy cost in general confined areas.     

Assessment of air dispersion characteristic in underground mine ventilation: Field measurement and numerical evaluation

The environmental safety of an underground mine depends strongly on its ventilation system. An efficient ventilation system provides fresh air, removes hazardous gases and dust, and maintains the temperature and humidity at appropriate levels. One of the most important factors in removing hazardous gases and dust is the dispersion behaviour in the mine network. This factor determines the longitudinal spreading and the average air residence time of gases or particulate matter throughout the mine. This paper describes tracer gas measurement in an underground mine and the utilisation and analysis of the dispersion characteristics using numerical simulations. The concentration–time curve obtained from the measurement is simulated to evaluate the effective diffusion coefficient that reflects the general dispersion characteristic of an entire mine. The evaluated values of effective diffusion coefficient are then compared to other data from several studies. The diffusivities obtained in this study were higher than other analytical and empirical results. More research is still required to identify the main factors causing such higher diffusivities. However, the results from the present work can be an important standpoint for future work. Numerical simulation conducted in this research was confirmed to be effective in detecting several leakage paths occurring in the mine ventilation network.     

Pollution Haven and Corruption Paradise

In this paper, we present a simple theoretical extension from the Economic Geography literature to characterize the main features of pollution havens (lax environmental regulation, good market access to high-income countries and corruption opportunities). Using structural and reduced-form estimations, we find that pollution havens are not a “popular myth” for European firms, laxer environmental standards significantly explain the location choice of polluting affiliates. We analyze in depth the role of trade costs (using various bilateral and multilateral measures), a 1% increase in access to the European market from a pollution haven fosters relocation there by 0.1%. We also find that corruption lowers environmental standards, which strongly attract polluting firms: a 1% increase of corruption fuels relocation by 0.28%. We test the economic significance of these empirical findings via simulations. The protection of the European market (e.g., a carbon tax on imports) to stop relocations to pollution havens must be high (a decrease of the European market for Morocco and Tunisia equivalent to 13%) not to say prohibitive (31% for China).     

A framework to measure the wildness of managed large vertebrate populations

As landscapes continue to fall under human influence through habitat loss and fragmentation, fencing is increasingly being used to mitigate anthropogenic threats and enhance the commercial value of wildlife. Subsequent intensification of management potentially erodes wildness by disembodying populations from landscape-level processes, thereby disconnecting species from natural selection. Tools are needed to measure the degree to which populations of large vertebrate species in formally protected and privately owned wildlife areas are self-sustaining and free to adapt. We devised a framework to measure such wildness based on 6 attributes relating to the evolutionary and ecological dynamics of vertebrates (space, disease and parasite resistance, exposure to predation, exposure to limitations and fluctuations of food and water supply, and reproduction). For each attribute, we set empirical, species-specific thresholds between 5 wildness states based on quantifiable management interventions. We analysed data from 205 private wildlife properties with management objectives spanning ecotourism to consumptive utilization to test the framework on 6 herbivore species representing a range of conservation statuses and commercial values. Wildness scores among species differed significantly, and the proportion of populations identified as wild ranged from 12% to 84%, which indicates the tool detected site-scale differences both among populations of different species and populations of the same species under different management regimes. By quantifying wildness, this framework provides practitioners with standardized measurement units that link biodiversity with the sustainable use of wildlife. Applications include informing species management plans at local scales; standardizing the inclusion of managed populations in red-list assessments; and providing a platform for certification and regulation of wildlife-based economies. Applying this framework may help embed wildness as a normative value in policy and mitigate the shifting baseline of what it means to truly conserve a species.     

When do environmental regulations backfire? Onsite industrial electricity generation,energy efficiency and policy instruments

More than half of all energy produced by electric utilities is lost in the form of waste heat. However, when manufacturing facilities choose to produce their own electricity, this waste heat is captured by Combined Heating and Power (CHP) technologies and used in the production process. As a result, manufacturers' pollution footprint can be dramatically reduced by choosing to produce electricity onsite rather than purchasing it from a utility. This paper uses Census microdata to study manufacturers’ decision to produce electricity onsite and examines how plants adjust onsite generation when they are subject to environmental regulations. Environmental regulations will backfire if they cause manufacturers to produce less electricity onsite and shift to electricity from less efficient, offsite electric utilities. We find that manufacturing plants subject to NOx command-and-control regulations decrease onsite electricity generation, increase electricity purchases from off-site utilities and see declines in their energy efficiency. However, manufacturers subject to cap-and-trade see no decline in onsite generation and experience improvements in energy efficiency. These findings demonstrate the importance of instrument selection and identify a new pathway through which emissions leakage may occur.     

Dams,Floodplain Land Use,and Riparian Forest Conservation in the Semiarid Upper Colorado River Basin,USA

Land and water resource development can independently eliminate riparian plant communities, including Fremont cottonwood forest (CF), a major contributor to ecosystem structure and functioning in semiarid portions of the American Southwest. We tested whether floodplain development was linked to river regulation in the Upper Colorado River Basin (UCRB) by relating the extent of five developed land-cover categories as well as CF and other natural vegetation to catchment reservoir capacity, changes in total annual and annual peak discharge, and overall level of mainstem hydrologic alteration (small, moderate, or large) in 26 fourth-order subbasins. We also asked whether CF appeared to be in jeopardy at a regional level. We classified 51% of the 57,000 ha of alluvial floodplain examined along >2600 km of mainstem rivers as CF and 36% as developed. The proportion developed was unrelated to the level of mainstem hydrologic alteration. The proportion classified as CF was also independent of the level of hydrologic alteration, a result we attribute to confounding effects from development, the presence of time lags, and contrasting effects from flow alteration in different subbasins. Most CF (68% by area) had a sparse canopy (50% canopy cover occupied <1% of the floodplain in 15 subbasins. We suggest that CF extent in the UCRB will decline markedly in the future, when the old trees on floodplains now disconnected from the river die and large areas change from CF to non-CF categories. Attention at a basinwide scale to the multiple factors affecting cottonwood patch dynamics is needed to assure conservation of these riparian forests.     

Influence of vertical greening design of building opening on indoor cooling and ventilation

This study focused on greening designs for building openings. Field experimentation was conducted and Computational Fluid Dynamics (CFD) software was used for simulation in order to analyze the influence of different greening design modes on indoor temperature. A greening design mode suitable for the opening of houses in Kaohsiung was proposed. This study took an architectural space with a pitched roof as the experimental site, where the main variable was the location of the plant facade outside the opening, and the distance between the plant and wall surface, as well as the number of plant layers, was the control variable. A plant (Rose of China) was selected for experimentation, and the indoor temperature distributions under various research module settings were discussed by numerical simulation. The conclusions are described, as follows: (1) The air temperature would be affected by the plants, and the indoor air temperature is reduced (over 0.5°C without direct sunshine in this study). (The difference between the indoor cooling effects with and without plants was 0.89~1.11°C. (2) While the cooling effect of the double-layer plant on indoor air temperature was better than a single-layer plant, the difference was limited and not proportional. (3) The plants should be located as close to the opening as possible, and be arranged partially sparse and partially dense. (4) When the outside wind speed is low, plant greening is highly recommended for cooling.