长三角城市群污染输送相互影响的敏感性试验

利用WRF-Chem模式,对2013年11月29日至12月11日长江三角洲地区的严重空气污染事件进行数值模拟,研究长三角核心区不同污染物本地源和外来输送所占比重。分析长三角核心区排放源对本地不同污染物浓度的污染贡献。结果表明,在2013年12月的这一次污染事件中,颗粒物平均本地贡献与外来输送基本比重相当;而SO_2、CO、NH_3、NO_x这4种气体污染物则以本地贡献为主,本地贡献的差异与气体的化学反应活性有关,活性越强本地贡献比重越大。污染过程中12月7日至12月9日00:00为污染最严重的时段,污染物的本地贡献有明显上升。区域间输送的方向和强度与地面风向、风速有紧密的联系。在边界层高度范围内,大部分污染物越往高空本地排放源的贡献越弱,外来输送主导作用增强,而硝酸盐在地面、1 km和1.5 km的本地贡献差异远小于其他污染物。     

An air quality balance index estimating the total amount of air pollutants at ground level

A new index named Air Quality Balance Index (AQBI), which is able to characterise the amount of pollution level in a selected area, is proposed. This index is a function of the ratios between pollutant concentration values and their standards; it aims at identifying all situations in which there is a possible environmental risk even when several pollutants are below their limit values but air quality is reduced. AQBI is evaluated by using a high-resolution three-dimensional dispersion model: the air concentration for each substance is computed starting from detailed emissions sources: point, line and area emissions hourly modulated. This model is driven with accurate meteorological data from ground stations and remote sensing systems providing vertical profiles of temperature and wind; these data are integrated with wind and temperature profiles at higher altitudes obtained by a Local Area Model. The outputs of the dispersion model are compared with pollutant concentrations provided by measuring stations, in order to recalibrate emission data. A three-dimensional high resolution grid of AQBI data is evaluated for an industrial area close to Alessandria (Northern Italy), assessing air quality and environmental conditions. Performance of AQBI is compared with the Air Quality Index (AQI) developed by the U.S. Environmental Protection Agency. AQBI, computed taking into account all pollutants, is able to point out situations not evidenced by AQI, based on a preset limited number of substances; therefore, AQBI is a good tool for evaluating the air quality either in urban and in industrial areas. The AQBI values at ground level, in selected points, are in agreement with in situ observations.     

Numerical Model Inter-comparison for Wind Flow and Turbulence Around Single-Block Buildings

Wind flow and turbulence within the urban canopy layer can influence the heating and ventilation of buildings, affecting the health and comfort of pedestrians, commuters and building occupants. In addition, the predictive capability of pollutant dispersion models is heavily dependent on wind flow models. For that reason, well-validated microscale models are needed for the simulation of wind fields within built-up urban microenvironments. To address this need, an inter-comparison study of several such models was carried out within the European research network ATREUS. This work was conducted as part of an evaluation study for microscale numerical models, so they could be further implemented to provide reliable wind fields for building energy simulation and pollutant dispersion codes. Four computational fluid dynamics (CFD) models (CHENSI, MIMO, VADIS and FLUENT) were applied to reduced-scale single-block buildings, for which quality-assured and fully documented experimental data were obtained. Simulated wind and turbulence fields around two surface-mounted cubes of different dimensions and wall roughness were compared against experimental data produced in the wind tunnels of the Meteorological Institute of Hamburg University under different inflow and boundary conditions. The models reproduced reasonably well the general flow patterns around the single-block buildings, although over-predictions of the turbulent kinetic energy were observed near stagnation points in the upwind impingement region. Certain discrepancies between the CFD models were also identified and interpreted. Finally, some general recommendations for CFD model evaluation and use in environmental applications are presented.     

Local Air Quality Impacts due to Downwash Around Thermal Power Plants: Numerical Simulations of the Effect of Building Orientation

One of the primary adverse environmental impacts associated with power generation facilities and in particular thermal power plants is local air quality. When these plants are operated at inland areas the dry type cooling towers used may significantly increase ambient concentrations of air pollutants due to the building downwash effect. When one or more buildings in the vicinity of a point source interrupt wind flow, an area of turbulence known as a building wake is created. Pollutants emitted from relatively low level sources can be caught in this turbulence affecting their dispersion. In spite of the fact that natural gas-fired combined-cycle power plants have lower air emission levels compared to other power plants using alternative fossil fuel, they can still create significant local air pollution problems. In this paper, local air quality impacts of a natural gas-fired combined-cycle power plant located in a coastal area are compared with those of another natural gas-fired combined-cycle power plant having identical air emissions but located in an inland area taking into account differences in topography and meteorology. Additionally, a series of scenarios for the inland site have been envisaged to illustrate the importance of plant lay-out configurations paying particular attention to the building downwash effect. Model results showed that different geometrical configurations of the stacks and cooling towers will cause remarkable differences in ambient air pollutant concentrations; thus it is concluded that when selecting a plant site, a detailed site-specific investigation should be conducted in order to achieve the least possible ambient air pollution concentrations with the given emissions.     

Multipoint source method in air pollution modelling of cold start emission

The paper presents a new method of air pollution modelling on a micro scale. For estimation of concentration of car exhaust pollutants, each car is treated as an instantaneous moving emission source. This approach enables us to model time and spatial changes of emission, especially during cold and cool start of an engine. These stages of engine work are a source of significant pollution concentration in urban areas. In this work, two models are proposed: one for the estimation of emission after cold start of the engine and another for the prediction of pollutant concentration. The first model (defined for individual exhaust gas pollutants) enables us to calculate the emission as a function of time after the cold or cool start, ambient temperature and average speed of motion. This model uses the HBEFA database. The second mathematical model is developed in order to calculate the pollutant dispersion and concentrations. The finite volume method is applied to discretise the set of partial differential equations describing wind flow and pollutant dispersion in the domain considered. Models presented in this paper can be called short-term models on a small spatial scale. The results of numerical simulation of pollutant emission and dispersion are also presented.     

Validation of Urban Emission Inventories

Two emission validation methods are presented. The first method focuses on the precision of the emission factors and the accuracy of modelled traffic flows. Emission factors derived from the COPERT II methodology are compared with on-board emission measurements and modelled traffic flow rates are compared with observations. The second validation method focuses on the completeness of the inventory, i.e. coverage of all sources. The method compares measured pollutant fluxes in the urban plume with the downwind transported and dispersed emissions integrated over plume width and mixing height. Both methods seem to indicate that traffic emission factors used in the urban emission inventories show large uncertainties. Besides the lack of measurement precision this is mainly induced by external influence factors like driving behaviour and vehicle maintenance.     

大气污染物排放调查监测研究进展

系统总结了当前大气污染物排放调查监测的主要方法及其在全球、区域、局地等不同尺度的典型应用，分析了地面监测、模型模拟与遥感反演3种方法受排放源多样、成分复杂、时空变异显著等因素影响，在尺度效应、成分解析等方面存在的问题。从优化监测方法、改进监测模式、融合监测技术等角度，提出了构建现代化大气污染物排放调查监测网络、开展污染物在不同排放阶段的变化解析研究及在不同圈层间的迁移全过程研究等建议。     

Numerical simulation on pollutant dispersion from vehicle exhaust in street configurations

The impact of the street configurations on pollutants dispersion from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard kappa - epsilon turbulence model, which was numerically solved based on Reynolds-averaged Navier-Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three cases of street configurations: (1) a regular-shaped intersection, (2) a T-shaped intersection and (3) a Skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably well with wind tunnel results. The results obtained indicate that the mean horizontal velocity was very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and Skew-shaped street intersections. Moreover, the results reveal that the street intersections are important factors to predict the flow patterns and pollutant dispersion in street canyon.     

复杂岩溶条件下锰矿尾矿库地下水溶质运移特征数值模拟研究

受构造、地层等复杂地质情况综合影响的岩溶地区地下水,其溶质运移及流场模拟向来是水文地质、环境地质研究中的难点。以贵州省松桃县某锰矿尾矿库为例,在充分分析研究区周边水文地质、环境地质条件的基础上,建立地质模型,概化边界条件,利用有限元软件FEFLOW进行流场拟合。在此基础上,模拟特征污染物锰及氨氮的弥散情况。模拟结果表明,在不做任何防渗处理的情况下,特征污染物将在F201断层、地层产状等边界条件的影响下汇入地下暗河,最终流入地表水系及地下水系,流向东部的松江河。因此,必须对锰矿尾矿库采取防渗措施,从而降低其对地下水、地表水的污染风险。     

Modelling of Fluid Flow and Pollutant Dispersion in a Street Canyon

A two-dimensional steady state numerical simulation has been carried out for a typical street canyon ventilated by a cross-wind. The PHOENICS package from CHAM was used to solve for the air flow above and within the street canyon. The k-epsilon turbulence model was used for turbulence modelling and pollutant sources were added at ground level over the road but not over the pavements. Results for the air flow showed the formation of a longitudinal vortex within the street canyon, as found by other researchers. Pollutant concentrations were predicted with the highest values occurring at the leeward walls of the upwind buildings, and the lowest values on the windward walls of the downwind buildings. The accuracy of these simulations was examined by comparing the predicted results with field observations. Reasonable agreement was obtained, confirming the difference between concentrations on the leeward and windward walls. The results show that the dispersion characteristics can be simulated in terms of structural configurations.     

大气污染物指纹系统构建及在污染溯源中的应用

基于污染物检测特征信息结合区域产业结构、企业布局等信息构建了大气污染物指纹系统,通过污染物检测特征信息构建的第一级指纹数据库实现了对大气特征污染物的识别和污染物应急处置措施的推送;通过污染源行业及其排放的特征污染物信息构建的第二级指纹数据库实现了产排污行业的溯源;通过企业及其产排污信息,结合气象条件构建的第三级指纹数据库实现了对产排污企业的溯源。基于大气污染物指纹数据库的污染溯源技术为突发环境污染事故中污染物质的识别和污染源的追踪提供了新途径。实际应用验证表明,大气污染物指纹系统污染溯源响应快速、识别精准,实现了大气污染物从监测、溯源到应急处置的全过程无缝衔接。     

Human exposure, health hazards, and environmental regulations

United States environmental regulations, intended to protect human health, generally fail to address major sources of pollutants that endanger human health. These sources are surprisingly close to us and within our control, such as consumer products and building materials that we use within our homes, workplaces, schools, and other indoor environments. Even though these indoor sources account for nearly 90% of our pollutant exposure, they are virtually unregulated by existing laws. Even pollutant levels found in typical homes, if found outdoors, would often violate federal environmental standards. This article examines the importance of human exposure as a way to understand and reduce effects of pollutants on human health. Results from exposure studies challenge traditional thinking about pollutant hazards, and reveal deficiencies in our patchwork of laws. And results from epidemiological studies, showing increases in exposure-related diseases, underscore the need for new protections. Because we cannot rely solely on regulations to protect us, and because health effects from exposures can develop insidiously, greater efforts are needed to reduce and prevent significant exposures before they occur. Recommendations include the development and use of safer alternatives to common products, public education on ways to reduce exposure, systematic monitoring of human exposure to pollutants, and a precautionary approach in decision-making.     

Inventory of emissions of primary air pollutants in the city of Kocaeli, Turkey

This study aims to obtain a reliable inventory of the emission rates of the principal air pollutants including PM, SO2, NOx) and CO in Kocaeli, Turkey. In the first stage, the pollutant sources classified as point, area and line sources are determined in the area. Then the annual emission rates of the pollutants released from these sources are estimated by the emission factors given by USEPA and CORINAIR. Results show that the annual emission rates for PM, SO2, NOx) and CO are 2195 tons, 5342 tons, 14632 tons and 23095 tons, respectively. On the other hand, the pollutant group with the highest contribution to total emission rate is determined as the point sources for NOx, which is responsible for 73% of total NOx emission, while it is the area sources for PM, SO2 and CO with the contribution percentages of 75, 76 and 69, respectively.     

秸秆焚烧对哈尔滨市灰霾天气的影响

2015年11月1—4日,哈尔滨市及周边地区发生了连续的灰霾天气,颗粒物浓度急剧升高。污染发生时,监测仪器均布设在哈尔滨市区上风向30 km处(哈尔滨市双城区)并开展了连续96 h的监测分析。综合利用气象观测资料,3D可视激光雷达监测资料及地面空气污染监测资料分析了灰霾天气发生的气象条件和污染边界层特征,根据哈尔滨市双城区大气污染物排放源谱库对主要成分进行来源解析,结合颗粒物质量浓度和气象条件研究了秸秆焚烧对灰霾天气的影响。结果表明,灰霾天气持续期间,夜间生物质燃烧源成为该地区颗粒物的第二大源;秸秆焚烧产生的大气污染物,由于地面长时间静风,污染边界层降低等原因,致使本地污染物累积、不易扩散,加剧了本次污染。     

利用综合指标和一元分布拟合筛选重点污染源

首次将综合指标和数理统计一元分布拟合方法运用于重点污染源的筛选,通过筛选排污量离群单位来确定重点污染源.研究了污染物排放量的分布,污染源各污染物排放量之间的关系;在进行重点污染源的筛选时,针对污染源所处不同地理位置或不同排放去向,可造成不同危害程度的问题,采取了对污染源所处地理位置或排放去向进行加权的方法;针对当污染源排放多种污染物,多参数筛选难于综合考虑的问题,提出了采用综合参数进行筛选的方法.采用的重点污染源的筛选方法更具有理论依据和科学性.     

A Numerical Study of Airflow and Pollutant Dispersion Inside an Urban Street Canyon Containing an Elevated Expressway

The goal of this study is to investigate numerically the wind flow and pollutant dispersion within an urban street canyon containing an elevated expressway and reveal the impacts of elevated expressway on the atmospheric environment in the canyon. A two-dimensional numerical model for simulating airflow and pollutant dispersion inside urban street canyons is first developed based on the Reynolds-averaged Navier–Stokes equations coupled with the standard k???ε turbulence model and the convection–diffusion equation for passive species transport, and then it is validated against a wind tunnel experiment. It was found that the model-predicted results agree well with the experimental data. Having established this, the wind fields and pollutant distributions in the canyon containing an elevated expressway are evaluated. The numerical results show that the expressway height above the street floor and the gap distance between the expressway and the building wall have considerable influence on airflow and pollutant level inside a canyon: (1) the vortical flow structure in the canyon varies with the expressway height for a constant gap distance, under certain expressway heights, only one main clockwise vortex is formed, while under others one main vortex as well as one or two secondary vortices above and below the expressway are created; (2) the pollutant level within the canyon increases when an expressway is placed in the canyon, especially when the expressway height equals the building height the flow velocities in the canyon are drastically reduced and air exchange in and above the canyon is seriously impeded by the expressway, which leads to a much higher pollution level in the canyon; and (3) the wider gap distance is favorable to pollutant removal from the canyon.     

长株潭区域一次重度污染过程气象成因

利用PM_2.5质量浓度、地面气象要素、NCEP、ERSST＿V3、GBL等资料，研究了2021年12月7—11日长株潭地区一次重度空气污染过程的特征及成因。结果表明，高空平直环流、无明显槽脊影响，地面弱冷空气活跃是本次重度空气污染过程的主要环流形势特征；地面均压场、小风和升温增湿是此次重度空气污染过程的主要气象要素特征。污染物浓度变化与主导风向和污染通道密切相关，本地风速对混合层的高度、污染物水平扩散影响较大，600～700 hPa逆温层有利于污染物在主导风作用下近距离传输及在低层交换积累。我国中东部污染物积聚是长株潭区域重要的污染来源，长株潭地区存在区域性同步污染现象。低层流入长株潭区域气流轨迹差异及地理条件是长株潭污染物空间分布差异的重要因素。     

Developing an indicator for the chronic health impact of traffic-related pollutant emissions

The goal of this study is to develop an emission based indicator for the health impact of the air pollution caused by traffic. This indicator must make it possible to compare different situations, for example different Urban Travel Plans, or technical innovations. Our work is based on a literature survey of methods for evaluating health impacts and, more particularly, those which relate to the atmospheric pollution caused by transport. We then define a health impact indicator based on the traffic emissions, named IISCEP for Chronic health impact indicator of pollutant emission. Here health is understood in a restricted meaning, excluding well-being. Only primary pollutants can be considered, as the inputs are emission data and an indicator must be simple. The indicator is calculated as the sum of each pollutant emission multiplied by a dispersion and exposition factor and a substance specific toxicity factor taking account of the severity.Last, two examples are shown using the IISCEP: comparison between petrol and diesel vehicles, and Nantes urban district in 2008 vs 2002.Even if it could still be improved, IISCEP is a straightforward indicator which can be used to gauge the chronic effects of inhaling primary pollutants. It can only be used in comparisons, between different scenarios or different technologies. The quality of the emissions data and the choice of the pollutants that are considered are the two essential factors that determine its validity and reliability.     

洞庭湖区一次重度空气污染过程成因分析

利用AQI和PM_(2. 5)质量浓度、地面气象要素、NCEP、ERSST_V3、GBL等资料,对2016年12月29日至2017年1月5日洞庭湖区一次重度空气污染过程成因进行了分析。结果表明,静稳天气形势下的累积效应和本地持续升温、降压、增湿、小风导致污染物浓度不断增加。本地风速与雨量对污染物浓度产生显著影响。降温前风速明显加大,有利于污染物快速扩散。湿度增加有利于污染物吸湿性增长,但高湿易引起降水有利于污染物的湿清除。此次重度空气污染过程中大气稳定度为中性或稳定,14:00混合层高度逐渐降低且重度空气污染日降至100 m以下。污染物空间分布与主导风向和污染通道密切相关。气流后向轨迹分析表明,洞庭湖区各地气流来源和影响路径差异明显,且存在大范围区域性同步污染现象。北方外来污染源是洞庭湖区重要的污染面源,本地工业污染排放点源和地理条件也是洞庭湖区空气污染物空间分布差异的重要因素。     

Characterisation of particulate matter on the receptor level in a city environment

Airborne particulate matter (PM) has become one of the dominant pollutants with the increasing material and energy demand due to global economic growth. The main objective of this research is to provide a comprehensive receptor level characterisation of the particulate matter collected in a city environment. Particulate matter samples were collected on Tapered Element Oscillating Microbalance (TEOM) filters from five monitoring sites over a period of 1 year. An Andersen eight-stage cascade impactor was also used to collect airborne PM samples from three other locations to compare with the samples collected by TEOM. All the samples were then subjected to individual particle morphology and chemical composition analysis by SEM/EDS. Bulk chemical composition of the samples were also analysed through ICP–OES. Based on these analyses, possible sources of the PM samples were identified. The results showed that the monitoring sites in residential environments were dominated by transportation-derived particles and other migratory particulates. Monitoring sites near the city centre were dominant by particles from transportation, with biological particles abundant for the site closer to a river. The monitoring station located close to the industrial area, despite only 200 m away from a motorway, has low contribution of non-exhaust particulates from vehicles. Instead, the particulates collected from this site were dominated by industrial sources. An air dispersion modelling package was also used to model the particulate matter dispersion in the city area for the period of sampling. The results from the model showed that the points of high emissions were around industrial areas.