中美燃煤火电厂空气污染物排放标准比较研究

本文对中美燃煤火电厂国家行业排放标准的内容设置、限值形式、监测、记录和报告规定,以及固定源排污许可证中如何执行排放标准进行了比较。相对于美国,中国燃煤火电厂国家行业排放标准文本内容过于简略,限值形式设置单一,主要采用全国统一的浓度限值而不是采用绩效限值;浓度限值的制定基于部分样本源而不是全部源的数据,很难体现行业的排放控制技术水平;达标判据不科学,也过于严格,小时均值的考核方式影响了火电厂的生产安排;排放标准中监测配套规定单薄,与环境监测的一般规定衔接性不佳,针对性差;记录和报告要求缺位,不能满足排污许可证管理的需求。建议参照美国行业排放标准的内容形式,排放限值采用绩效限值形式,并规定长平均周期的考核要求,将与之配套的监测、记录和报告要求纳入排放标准,以满足固定源排污许可证制度的需求。     

Evaluation of approaches to calculate critical metal loads for forest ecosystems

This paper evaluates approaches to calculate acceptable loads for metal deposition to forest ecosystems, distinguishing between critical loads, stand-still loads and target loads. We also evaluated the influence of including the biochemical metal cycle on the calculated loads. Differences are illustrated by examples of Cd, Cu, Pb and Zn for a deciduous forest on five major soil types in the Netherlands. Stand-still loads are generally lower than critical loads, which in turn are lower than the target loads indicating that present levels are below critical levels. Uncertainties in the calculated critical loads are mainly determined by the uncertainty in the critical limits and the chemical speciation model. Including the metal cycle has a small effect on the calculated critical loads. Results are discussed in view of the applicability of the critical load concept for metals in future protocols on the reduction in metal emissions.     

Polybrominated diphenyl ethers in food and associated human daily intake assessment considering bioaccessibility measured by simulated gastrointestinal digestion

The concentrations of PBDEs in 299 vegetable and animal-based food samples of 31 species, collected in Shanghai, China, and the bioaccessibility of PBDEs in part of the samples were determined. The PBDE concentrations ranged from 0 to 1245.4 pg g⁻¹ with animal-based food containing more PBDEs than vegetables. The bioaccessibility of PBDEs, determined by a method simulating human gastrointestinal digestion process, were from 2.6% to 39.9% in vegetables, and from 5.2% to 105.3% in animal-based food. For animal-based food, good correlations were observed between the bioaccessibility of PBDEs and the fat content, thus the fat content in animal-based food was able to be used to estimate the bioaccessibility of PBDEs. The total daily intake of PBDEs via ingestion of vegetables and animal-based food for an average Shanghai resident was estimated as 13 235.7 and 13 668.0 pg d⁻¹, respectively, but the amounts available for human absorption were reduced to 2674.4 and 4316.6 pg d⁻¹ after the PBDE bioaccessibility was considered. Finally, the contributions of different food groups to the total daily intake of PBDEs were evaluated. The results revealed that, when not considering the bioaccessibility of PBDEs, vegetables were the leading contributor (49.2%), followed by fish (34.0%). However, the sequence was reversed after the PBDE bioaccessibility was taken into account. The results indicated that human exposure to PBDEs via food ingestion might have been significantly overestimated and the exposure assessment could be misleading if the bioaccessibility of PBDEs was not considered.     

空气质量监测中标准状态对测定结果的影响及建议

环境空气质量标准中各种污染物的浓度限值是评价、考核空气质量状况的基本依据。为了保证在不同时空、不同环境状况下监测数据的可比性,各个国家或组织在制定的空气质量标准中对标准状态(温度和压力)进行了定义。但是,由于标准状态定义不同,即使是同一环境状况下的同一实测结果进行标化计算后的污染物浓度也不相同,达不到可比性的基本原则。因此,建议中国在未来修订空气质量标准所采用的标准状态,进一步与国际接轨。     

应用等效质量方法确定间接排放企业的排污许可限值——以常州市为例

排污许可证制度是实施总量控制和减排任务的重要手段,是改善流域水环境质量的有效措施。间接排放企业是排污许可管理的重要对象,其排污许可限值是排污许可证发放的核心内容,我国关于间接排放企业排污许可限值的核定还没有统一的规定。通过借鉴美国国家污染物排放削减系统(NPDES)预处理机制,提出采用等效质量方法来确定间接排放企业排污许可限值,并以常州市某污水处理厂为研究对象,对该污水处理厂接纳的6家间接排放企业的污染物排污许可限值进行了研究。结果表明:采用等效质量方法计算出6家企业的等效质量负荷限值,结合我国现有排放标准浓度限值,可确定6家纳管企业COD_Cr的排污许可限值。等效质量方法在新建接管企业、现有企业停止接管和提高水质排放标准等多种情况下,能兼顾纳管企业的个体差异,方便灵活、便于应用。     

基于周围环境目标值估算的企业边界大气污染物限值分析

从40余项国家大气固定污染源污染物排放标准以及地方恶臭污染物排放标准中筛选出已制定企业边界限值的36种大气污染物,提出适用于限值分析的方法,基于周围环境目标值（AMEG）设置了参考区间,对比分析了我国与美国化学有害因素职业接触限值时间加权平均容许浓度（TWA）的差异。结果表明,36种大气污染物可分为3类：1）出现在国家大气污染物综合排放标准等制定和发布年限较长标准中且限值较为宽松的8种污染物;2）限值未受嗅阈值影响的13种污染物,其中12种污染物的限值与AMEG估算结果的8.4倍较为接近;3）限值受嗅阈值影响的15种污染物,其中部分污染物的限值接近AMEG估算结果,部分限值接近嗅阈值。参与对比分析的255种化学有害因素中,我国和美国的TWA相等的有44种,占比不超过20%,差异在±1倍之内的约占85%,在±5倍以上的约占7%。研究显示,现行大气污染物排放标准中的企业边界限值有效保护了人体健康和生态环境,应对制定和发布年限较长且限值较为宽松的标准,以及限值高于嗅阈值的标准开展研究,分析限值的合理性。在制定企业边界大气污染物限值时,应广泛收集更多来源的职业接触限值数据并分析其适用性。

     

Safety parameters for oxygen-enriched flames

The utilization of low-quality gaseous fuel from biomass gasification and the abundance of oxygen-rich streams obtained as a by-product of nitrogen-air separation by membrane technology has incentivized the development of sustainable oxygen-enriched combustion technologies in the last decades. However, a dearth of experimental and numerical analysis addressing the reactivity and safety aspects of these mixtures at initial low temperatures can be observed in the current literature.In this work, the heat flux burner was adopted for the measurement of the laminar burning velocity of methane in oxygen enriched air at different equivalence ratios. Results were compared with numerical data obtained by means of detailed kinetic mechanisms developed at the University of Bologna and the Gas Research Institute (GriMech3.0). Simplified correlations for the estimation of the laminar burning velocity with respect to the oxygen content at any equivalence ratio were developed, tested and evaluated.An elemental reaction-based function was found appropriate for the estimation of the overall reactivity of the investigated mixtures. Besides, numerical analyses were performed to characterize the flame structures in terms of temperature and product distribution under several initial conditions. These results gave further insights into the reaction mechanisms of gaseous fuels in the case of oxygen-enriched air, highlighting potential bottlenecks for kinetic model refinements. Eventually, relevant safety parameters were estimated, in particular the flammability range of the fuel/oxidant mixture, in terms of lower and upper flammability limits.     

An investigation of flammability limits of gaseous mixtures at reduced pressures

An experimental investigation of flammability limits of hydrogen, methane and propane in air and oxygen at reduced pressures was carried out. A slow influence of sizes of an experimental vessel of a diameter higher than 125 mm on the flammability limits was revealed, but an influence of a type of an oxidizer (air or oxygen) and an ignition energy is significant. Critical values of an initial pressure for a possibility of a flame propagation were determined. The limiting values of the ignition energy were determined, for which an elevation of this parameter does not influence the critical pressure and the flammability region. A qualitative interpretation of obtained experimental results is given, which is based on a peculiarities of a flame initiation.     

Rethinking the native range concept

A species is not native outside its native range, but native range is not precisely defined. The invasion literature contains wide discussion of the core concepts such as naturalization, invasiveness, and ecological impact, but the concept of native range has received so little attention that a formal definition does not exist. I considered, among other impediments to a formal definition of native range, the sometimes arbitrariness of the spatial and temporal limits assigned to native range. Broad questions that remain include whether invasion theory can be used to define the native range for species without non-native ranges.     

Flow and flame visualization near the upper flammability limits of methane/air and propane/air mixtures at elevated pressures

In this study, direct visualization of flow and flame from the ignition of methane/air and propane/air mixtures near the UFL at elevated pressures of up to 2.0 MPa were obtained with a test cell comprised of double-sided plexiglass and a containment vessel with double-sided glass. These visualizations allowed direct observations of ignition and flame near UFL at elevated pressures. Two distinctive features were observed in ignition at elevated pressures that differ from those under ambient pressure: the hot igniter formed a convective plume, rather than a convection cell; and the flame initiated from the top of the test cell and propagated downwards, rather than directly from the igniter. Both these distinctive features are characteristics of convection at high Rayleigh number accompanied with increased gas density at elevated pressures. Our study also shows that visualization of the formation of planar flame provides the most objective criterion for defining flammability limits at elevated pressures.