基于空气质量模拟的江苏省大气污染物排放清单比较研究

大气污染物排放清单是空气质量模拟和空气污染治理的重要依据.本研究比较分析了两套覆盖江苏省的2017年大气污染物排放清单，即分别由上海市环境科学研究院、江苏省环境科学研究院编制的"长三角清单"和"江苏省清单"，并结合区域空气质量模型CMAQ评估不同清单对长三角地区2017年1、4、7、10月的空气质量模拟的影响.清单比较结果表明，除二氧化硫（SO₂）以外，江苏省清单估算的各污染物排放量较长三角清单低.通过与观测数据比较，发现两套清单对SO₂、氮氧化物（NO_x）、臭氧（O₃）和细颗粒物（PM_2.5）的模型模拟性能均较好.江苏省清单与长三角清单两者的模拟结果空间分布接近，其中江苏省清单模拟的PM_2.5和O₃在长三角多数地区略低于长三角清单的模拟结果（1月O₃除外）.江苏省清单与长三角清单均能够用于空气质量模式模拟，可为江苏地区的细颗粒物和光化学烟雾污染的控制策略制定提供参考.     

A Eulerian air pollution model for Europe with nonlinear chemistry

A long-range transport model with nonlinear chemical reactions is described. The model contains 35 pollutants and 70 chemical reactions. This is a Eulerian model defined on a space domain containing the whole of Europe. The spherical space domain (corresponding to the Earth's surface covered by the model) is mapped into a square plane domain and discretized by using a 32×32 grid. The grid increments are equidistant (both along the Ox axis and along the Oy axis). The choice of values of the physical parameters involved in the model and the numerical treatment of the model are shortly discussed. The model is tested with meteorological data for 1985 and 1989. The numerical results are compared with measurements at stations located in different European countries. Extensive comparisons of ozone concentrations for July 1985 with measurements taken at 24 European stations are also carried out. Results concerning three episodes in July 1985 as well as results obtained in the study of the sensitivity of the ozone concentrations to variations of NO _x and/or anthropogenic VOC emissions are presented. The advantages and the limitations of such a model are discussed. The model is continuously improved by adding new modules to it. The plans for improvements in the near future are outlined.     

Analysis of a regional model (EURAD) near surface gas concentration predictions using observations from networks

Summary The three-dimensional long-range transport model EURAD has been applied to two episodes in 1986 to study the transport and transformation of air pollutants over Europe under different meteorological conditions. The spring episode is characterized by varying meteorological conditions over Europe and transport of pollutants is complex. The summer episode is suitable to study the enhanced formation of photooxidants as an almost stagnant high pressure system over central Europe favoured the accumulation of pollutants. Available observations from several monitoring networks in Europe are used to evaluate the near surface concentration predictions of the model. This is possible for the sulfur species, O₃ and NO₂ for the central part of the modelling domain. It is shown that O₃ and NO₂ trends in the western part of the model domain are estimated reasonably well. The strong bias for underpredicting NO₂ in the eastern part of the domain reflects the quality of emission data for the two regions of the modelling area. Typically for regional scale Eulerian transport models when applied on larger grid sizes, EURAD overpredicts the observed minima and underpredicts the high observations. This is particularly true for O₃ but also detectable in the sulfate comparisons. Several sensitivity simulations for both episodes were performed to test numerical algorithms, parameterizations or emission data. Results from these simulations clearly show the important role of cloud related processes during the spring time for the sulfur species. Further testing and assessment of cloud parameterizations and emission data for transport models is anticipated.With 22 Figures     

The onset of separation in neutral,turbulent flow over hills

The onset of separation in turbulent, neutrally stratified, boundary-layer flow over hills is considered. Since the flows are fully turbulent, the occurrence of intermittent separation, in the sense of any reversal of near surface flow, will depend strongly on the detailed structure and behaviour of the turbulent eddies. Very little is known about such intermittent separation and the phenomenon cannot be studied with numerical models employing standard turbulence closures; eddy-resolving models are required. Therefore, here, as elsewhere in the literature, the arguably less physically significant process of mean flow separation is studied. Numerical simulations of flow over idealised two- and three-dimensional hills are examined in detail to determine the lowest slope, _crit, for which the mean flow separates.Previous work has identified this critical slope as that required to produce a zero surface stress somewhere over the hill. This criterion, when a mixing-length turbulence closure is applied, reduces to requiring the near-surface vertical velocity shear to vanish at some point on the hill's surface. By applying results from a recent linear analysis for the flow perturbations to this condition, a new expression for _crit is obtained. The expression is approximate but its relative simplicity makes it practically applicable without the need for use of a computer or for detailed mapping of the hill. The approach suggested differs from previous ones in that it applies linear results to a non-linear expression for the surface stress. In the past, a linear expression for the surface stress has been used. The proposed expression for _crit leads to critical angles that are about twice previous predictions. It is shown that the present expression gives good agreement with the numerical results presented here, as well as with other numerical and experimental results. It is also consistent with atmospheric observations.     

Aerodynamic Scaling for Estimating the Mean Height of Dense Canopies

We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h _a as the most effective means of resolving the representative canopy height for all forests. We determined h _a by simple linear regression between zero-plane displacement d and roughness length z ₀, without the need for stand inventory data. The applicability of h _a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h _a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z ₀ was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h _a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h _a was also verified using data from several previous studies.     

On the parameterization of drag over small-scale topography in neutrally-stratified boundary-layer flow

Predictions of the surface drag in turbulent boundary-layer flow over two-dimensional sinusoidal topography from various numerical models are compared. For simple 2D terrain, the model results show that the drag increases associated with topography are essentially proportional to (slope)² up to the steepness at which the flow separates. For the purposes of boundary-layer parameterisation within larger-scale models, we propose a representation of the effects of simple 2D topography via an effective roughness length, z ₀ ^eff. The form of the varation of z ₀ ^eff with terrain slope and topographic wavelength is established for small slopes from the model results and a semi-empirical formula is proposed.     

Review of the Field Measurements and Parameterization for Dust Emission During Sand-Dust Events

Dust emission generated by wind erosion is a basic process before the transport and deposition of dust particles. Parameterization of dust emission flux is important for accurate simulation and prediction of dust events. Field observation and numerical simulation are two approaches to understand the complex process of dust emission. Great progress has been made on the characteristics and mechanism of dust emission during dust storm events. This review introduces the major factors influencing dust emission and summarizes the calculation methods of several key parameters of dust emission, including the threshold friction velocity u.t, threshold wind speed Ut, streamwise saltation flux Q, and （vertical） dust emission flux F, from perspectives of both observation and parameterization. The paper also discusses the improvement, application, and validation of different dust emission schemes in dust models. Existing problems and future research directions are elaborated as well.     

1991年江淮特大暴雨的降水性质与对流活动

从计算大尺度热源和分析ＴＢＢ资料两个方面，阐述了１９９１年江淮梅雨期间降水性质与对流活动的季节性演变特征。结果表明：梅雨期间江淮上空３个强上升运动时段分别形成了３场暴雨，由暴雨释放的热量使江淮大气出现了３个时段的强加热；３场暴雨的降水性质呈显著的季节性演变，由第１场暴雨以锋面性降水为主发展到第３场暴雨异常强的对流性降水。文中详细分析了热源和水汽汇的时空分布特征，并从大气运动场和热力结构讨论了盛夏强对流降水期间积云对流以涡动形式对热量和水汽的强铅直输送作用。江淮地区ＴＢＢ值能很好地反映降水状况，雨期一致地对应于ＴＢＢ低于２５０Ｋ的时段。梅雨中后期东亚地区对流活动季节性地增强，带状对流区（特别是ＴＢＢ高负距平区）与雨带位置相符。对流带位置及对流活动强弱与西南暖湿气流活动密切相关，它很好地表征了东亚地区的低空急流（给积云输送热带对流大气）。梅雨期间对流带主要出现在江淮流域，但可在东亚范围内飘移，它落在江淮与否则决定了江淮暴雨的维持与中断     

Bulk Transfer Relations for the Roughness Sublayer

In the roughness sublayer (RSL), Monin–Obukhov surface layer similarity theory fails. This is problematic for atmospheric modelling applications over domains that include rough terrain such as forests or cities, since in these situations numerical models often have the lowest model level located within the RSL. Based on empirical RSL profile functions for momentum and scalar quantities, and scaling the height with the RSL height z _*, we derive a simple bulk transfer relation that accounts for RSL effects. To verify the validity of our approach, these relations are employed together with wind speed and temperature profiles measured over boreal forest during the BOREAS experimental campaign to estimate momentum and heat fluxes. It is demonstrated that, when compared with observed flux values, the inclusion of RSL effects in the transfer relations yields a considerable improvement in the estimated fluxes.     

Effects of shear and sharp gradients in static stability on two-dimensional flow over an isolated mountain ridge

Summary ?We have investigated the effects of shear and sharp gradients in static stability and demonstrated how a mountain wave and its associated surface winds can be strongly influenced. Linear theory for two-dimensional, nonrotating stratified flow over an isolated mountain ridge with positive shear and constant static stability shows that the horizontal wind speeds on both the lee and upslope surfaces are suppressed by positive shear. The critical F(=U/Nh where U is the basic wind speed, N the Brunt-Vaisala frequency, and h the mountain height) for the occurrence of wave breaking decreases when the strength of the positive shear increases, while the location for the wave-induced critical level is higher in cases with larger positive shear. The linear theory is then verified by a series of systematic nonlinear numerical experiments. Four different flow regimes are found for positive shear flow over a two-dimensional mountain. The values of critical F which separate the flow regimes are lower when the strength of the positive shear is larger. The location of stagnation aloft from numerical simulations is found to be quite consistent with those predicted by linear theory. We calculate the strongest horizontal wind speed on the lee surface (U _max), the smallest horizontal wind speed on the upslope surface (U _min), the reflection (Ref), and the transmission (Tran) coefficients for different combinations of the stability ratio between the upper and lower layers (i.e. and z ₁ (interface height) in a two-layer atmosphere from linear analytical solutions. Both Ref and Tran are found to be functions of log() but not the interface height (z ₁). Ref is larger when is much different from 1, no matter whether it is larger or smaller than 1. However, Tran decreases when log() increases and approaches 0 when log() is large. The magnitude of the largest U _max (smallest U _min) increases (decreases) as the absolute value of log() increases. It is found that the largest U _max occurs when the nondimensional z ₁ is near for cases with a less stable upper layer or when z ₁ is near for cases with a more stable upper layer. These results are confirmed by nonlinear numerical simulations. We find that linear theory is very useful in qualitative analysis of the possibility of high-drag state for different stability profiles. The location of stagnation aloft in a two-layer atmosphere from numerical simulations agrees very well with those predicted by linear theory. The above findings are applied to investigate the Boulder severe downslope windstorm of 11 January 1972. We find that the windstorm cannot develop if the near mountain-top inversion is located at a higher altitude (e.g.,  km). However, if there exists a less stable layer right below the tropopause, the windstorm can develop in the absence of a low-level inversion. These results indicate the importance of partial reflection due to the structured atmosphere in influencing the possibility of severe downslope windstorms, although partial reflection may not be the responsible mechanism for the generation of windstorms. Received September 25, 1999/Revised February 9, 2000     

下垫面非均匀流域的幂指数TOPMODEL的模拟研究

利用取消流域土壤表层饱和导水率0K、土壤饱和导水率有效衰减系数m和地下水补给速率R为空间均匀假设的幂指数TOPMODEL,对流域水量平衡各分量进行敏感性研究试验,揭示空间非均匀性对幂指数TOPMODEL模拟结果的影响。从特定研究流域所得结果中可得的主要结论有:1)0K、m和R的空间变化对流域的逐日地表径流和基流以及逐日总径流有影响,针对设定的0K、m和R的空间变化,其中m的空间变化较明显地增加了逐日地表径流和洪峰流量。2)就设定的0K、m和R的空间变化而论,对流域多年平均年总径流以及蒸发模拟结果影响不大,但改变了径流在地表径流和基流之间的分配;其中R的空间变化影响最显著,m和0K的空间变化影响则较小。     

北京城市下垫面动力学参数的计算与分析

采用北京325 m铁塔2008—2012年的单层超声观测资料,基于莫宁-奥布霍夫相似理论(Monin-Obukhov similarity theory)和前人提出的最小误差分析方法,计算了铁塔周边下垫面的零平面位移高度和动力粗糙度长度。结果表明,由于铁塔位于北京市区,其周边下垫面呈现极其复杂的非均匀性,所以对应铁塔周边不同的扇区,零平面位移高度和动力粗糙度长度各有不同。平均而言,在2008—2012年间,铁塔周边下垫面的零平面位移高度为34.4 m,动力粗糙度长度为1.16 m。此外,综合前人的计算结果发现,铁塔周边的零平面位移高度和动力粗糙度长度在2001年之前呈显著增加的趋势,而在2001年以后并未增长,这一现象与铁塔周边的城市化进程相对应。     

Investigating the Changes in Air Pollutant Emissions over the Beijing-Tianjin-Hebei Region in February from 2014 to 2019 through an Inverse Emission Method

In recent years, China has implemented several measures to improve air quality. The Beijing-Tianjin-Hebei(BTH)region is one area that has suffered from the most serious air pollution in China and has undergone huge changes in air quality in the past few years. How to scientifically assess these change processes remain the key issue in further improving the air quality over this region in the future. To evaluate the changes in major air pollutant emissions over this region, this paper employs ens...     

A Model to Estimate Global Radiation in Complex Terrain

Global radiation is an important parameter necessary for most ecological models. However, in situ data barely meets the needs of modelling mountainous ecosystems since most field stations are located in flat areas. Consequently, it is usually necessary to extrapolate radiation measurements obtained from an adjacent flat area to the complex terrain of concern. The distribution of radiation in complex terrain depends upon two factors: the local atmospheric conditions, which determine the radiation potentially available to a supposed flat surface in a given location, and the topographic effects on this possible radiation. The latter have been included in detail in most radiation models for complex terrain, but the former are often only simply treated as constant or estimated by over-simplified empirical algorithms. In this paper we propose a novel model that uses a parametric atmospheric model to calculate the potential radiation for a supposed flat surface in a given location, and then account for topographic effects. Direct radiation, diffuse radiation and reflected radiation are calculated separately in the model due to the distinctive characteristics of and the effects by topography. Based on the parametric model, this paper has investigated the relationship between radiation transmittance, clearness indices and altitude under a series of water vapour content and turbidity conditions. This combines three ratios, R _b, R _d, and R _r, defined as the direct radiation, diffuse radiation and reflected radiation received by the arbitrary surface, respectively, to their counterparts in the horizontal surface, to estimate the global radiation for any given location. The model has been validated with data from measurements in National Park Berchtesgaden, Germany, where six measurement sites with various altitudes and topographic characteristics have been deployed. The r ² of modelled and measured hourly global radiation are greater than 0.90 in all six sites, with RMSE varies from 16 to 100 W m⁻². Sensitivity analysis revealed that the model was not sensitive to change in water vapour content, which suggests the possibility to use an exponential algorithm of water vapour content when there is no in situ water vapour content information in complex terrains. The NRMSE was only reduced by 0.04, on average, in five of the six sites when water vapour content information was calculated from the in situ air temperature and relative humidity measurements.     

基于CMAQ-MCM模型的长三角地区夏季臭氧和大气氧化性影响的研究

传统的空气质量模型多使用简化的光化学反应机制来模拟大气污染物的形成.这些机制主要基于烟雾箱实验拟合的反应速率和产物来模拟二次产物（如臭氧（O₃））前体物的氧化反应,具有一定的不确定性,导致模拟结果产生偏差.针对该问题,本研究将详细的大气化学机理（MCMv3.3.1）与美国国家环境保护局研制的第三代空气质量预报和评估系统CMAQ相结合（CMAQ-MCM）,模拟研究长三角地区2015年8月27—9月5日臭氧高发时段的空气质量.CMAQ-MCM模型可以较好地模拟长三角地区6个代表城市O₃和其前体物随时间的变化趋势.对模拟的O₃日最大8 h平均浓度的统计分析表明,徐州表现最好（标准平均误差=-0.15,标准平均偏差=0.23）.在长三角地区,居民源对挥发性有机物（VOCs）的贡献最大,占39.08%,其次是交通运输（33.25%）和工业（25.56%）.能源对总VOCs的贡献最小,约为2.11%.对活性氧化氮（NO_y）的分析表明,其主要组分是NO_x（80%）,其次是硝酸（HNO₃）（<10%）.O₃的空间分布与NO_y和NO_x非常相似.HCHO等其他氧化产物的分布与NO_x相似,这很可能是由于在高NO_x条件下VOCs氧化产生的产物.甲基乙烯基酮（MVK）和甲基丙烯醛（MACR）的空间分布与自然源VOCs （BVOCs）非常相似,表明长三角地区MVK和MACR主要由BVOCs氧化生成.长三角地区受到人为源和自然源排放相互作用的影响.     

长江中下游6—7月降水的降尺度模型

基于偏相关的强迫因子选取方法,以长江中下游6—7月降水为例,进行了降水变率的归因分析,并建立了相应的统计降尺度模型。结果表明,影响长江中下游6—7月降水的强迫因子主要有两个:西太平洋850 h Pa的位势高度(W_(PH8))和黑潮延伸区的海表温度(K_(SST))。W_(PH8)反映的是西太平洋副热带高压对长江中下游降水的影响;K_(SST)反映了黑潮延伸区的变率。基于这两个因子的线性降尺度模型能较好地拟合长江中下游6—7月的降水,在独立检验和模式检验阶段,模型体现出了可靠性,因而可用于长江中下游降水的季节预测。     

Subfilter-scale Fluxes over a Surface Roughness Transition. Part I: Measured Fluxes and Energy Transfer Rates

A wind-tunnel experiment was designed and carried out to study the effect of a surface roughness transition on subfilter-scale (SFS) physics in a turbulent boundary layer. Specifically, subfilter-scale stresses are evaluated that require parameterizations and are key to improving the accuracy of large-eddy simulations of the atmospheric boundary layer. The surface transition considered in this study consists of a sharp change from a rough, wire-mesh covered surface to a smooth surface. The resulting magnitude jump in aerodynamic roughnesses, M = ln(z ₀₁/z ₀₂), where z ₀₁ and z ₀₂ are the upwind and downwind aerodynamic surface roughnesses respectively, is similar to that of past experimental studies in the atmospheric boundary layer. The two-dimensional velocity fields used in this study are measured using particle image velocimetry and are acquired at several positions downwind of the roughness transition as well as over a homogeneous smooth surface. Results show that the SFS stress, resolved strain rate and SFS transfer rate of resolved kinetic energy are dependent on the position within the boundary layer relative to the surface roughness transition. A mismatch is found in the downwind trend of the SFS stress and resolved strain rate with distance from the transition. This difference of behaviour may not be captured by some eddy-viscosity type models that parameterize the SFS stress tensor as proportional to the resolved strain rate tensor. These results can be used as a benchmark to test the ability of existing and new SFS models to capture the spatial variability SFS physics associated with surface roughness heterogeneities.     

Instability in Lagrangian stochastic trajectory models,and a method for its cure

A number of authors have reported the problem of unrealistic velocities (“rogue trajectories”) when computing the paths of particles in a turbulent flow using modern Lagrangian stochastic (LS) models, and have resorted to ad hoc interventions. We suggest that this problem stems from two causes: (1) unstable modes that are intrinsic to the dynamical system constituted by the generalized Langevin equations, and whose actual triggering (expression) is conditional on the fields of the mean velocity and Reynolds stress tensor and is liable to occur in complex, disturbed flows (which, if computational, will also be imperfect and discontinuous); and, (2) the “stiffness” of the generalized Langevin equations, which implies that the simple stochastic generalization of the Euler scheme usually used to integrate these equations is not sufficient to keep round-off errors under control. These two causes are connected, with the first cause (dynamical instability) exacerbating the second (numerical instability); removing the first cause does not necessarily correct the second, and vice versa. To overcome this problem, we introduce a fractional-step integration scheme that splits the velocity increment into contributions that are linear (U _i ) and nonlinear (U _i U _j ) in the Lagrangian velocity fluctuation vector U, the nonlinear contribution being further split into its diagonal and off-diagonal parts. The linear contribution and the diagonal part of the nonlinear contribution to the solution are computed exactly (analytically) over a finite timestep Δt, allowing any dynamical instabilities in the system to be diagnosed and removed, and circumventing the numerical instability that can potentially result in integrating stiff equations using the commonly applied explicit Euler scheme. We contrast results using this and the primitive Euler integration scheme for computed trajectories in a drastically inhomogeneous urban canopy flow.     

Factors affecting levels of aerosol sulfate and nitrate on the Western Mediterranean coast

The present study was carried out between October 2003 and September 2004 at an urban background station near the Mediterranean coast in southeastern Spain. The sulfate and nitrate content was determined in 332 PM10 and PM2.5 daily samples. The results show that the seasonal variation of nitrate measured in PM10 does not correspond with what has been observed at other locations in the Iberian Peninsula, where the minima are reached during the summer months due to decomposition of ammonium nitrate at high temperatures. The recorded levels of PM10 nitrate were slightly higher in summer due to an increase in the concentrations of coarse mode nitrate. On the contrary, both the concentrations and the percentages of nitrate in PM2.5 were lowest from June to September. The sulfate levels in both PM10 and PM2.5 were maxima in summer because the oxidation rate of SO₂ increases with solar radiation. An elevated correlation (0.72 < r < 0.92) between the monthly average concentrations and percentages of sulfate and solar radiation has been found. We have also investigated the influence that Saharan dust intrusions and high pollution episodes have upon the sulfate and nitrate concentrations. Both types of events increased NO₃⁻ and SO₄²⁻ levels, particularly the high pollution episodes.