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1.
北京秋季一次典型大气污染过程多站点分析   总被引：3，自引：1，他引：2  
多站点多种大气污染物的同步在线观测对深入剖析大气污染的成因和演变机制有重要意义。以龙潭湖、北京325 m塔、双清路和阳坊4监测站点实时NOx、SO2、O3、PM2.5和PM10浓度观测数据为基础,介绍了北京地区2010年10月3～11日发生的一次典型污染过程。不同污染物在污染过程中变化特征不一致,表现为NOx、SO2、O3浓度有明显日变化,而PM浓度升高后一直维持在高值,日变化幅度很小。通过分析不同站点、相同污染物之间的相关性和变异系数发现,4站点间一次污染物NO和SO2空间浓度差别大,变异系数分别为77%和70%,相关系数低于0.44;而二次污染物NO2、PM2.5、O3空间浓度差别较小,变异系数分别为34%、36%和29%,相关系数均超过0.54。结合中尺度气象模式研究发现,该污染过程中,850 hPa高空持续的西南暖平流造成华北地区显著平流逆温,与近地层辐射逆温共同作用,使北京地区混合层高度维持在1200 m以下。低混合层高度和低风速限制了大气垂直和水平扩散,造成北京地区近地层污染物累积,形成重度污染。  相似文献   

2.
The dispersion of a point-source release of a passive scalar in a regular array of cubical, urban-like, obstacles is investigated by means of direct numerical simulations. The simulations are conducted under conditions of neutral stability and fully rough turbulent flow, at a roughness Reynolds number of Re τ  = 500. The Navier–Stokes and scalar equations are integrated assuming a constant rate release from a point source close to the ground within the array. We focus on short-range dispersion, when most of the material is still within the building canopy. Mean and fluctuating concentrations are computed for three different pressure gradient directions (0°, 30°, 45°). The results agree well with available experimental data measured in a water channel for a flow angle of 0°. Profiles of mean concentration and the three-dimensional structure of the dispersion pattern are compared for the different forcing angles. A number of processes affecting the plume structure are identified and discussed, including: (i) advection or channelling of scalar down ‘streets’, (ii) lateral dispersion by turbulent fluctuations and topological dispersion induced by dividing streamlines around buildings, (iii) skewing of the plume due to flow turning with height, (iv) detrainment by turbulent dispersion or mean recirculation, (v) entrainment and release of scalar in building wakes, giving rise to ‘secondary sources’, (vi) plume meandering due to unsteady turbulent fluctuations. Finally, results on relative concentration fluctuations are presented and compared with the literature for point source dispersion over flat terrain and urban arrays.  相似文献   

3.
The concentrations of air pollutants depend on meteorological conditions and pollutant emission level. From the statistical properties of air pollutants the number of times the daily average concentrations exceed the assigned air quality standard (AQS) can be estimated, as well as the level of reduction of particle matter emission sources required to meet the AQS. In this paper three statistical distributions (lognormal, Weibull and type V Pearson distribution) were used to fit the complete set of PM10 data for the Belgrade urban area during a three-year period (2003–2005). The method of moments and the method of least squares were both used to estimate the parameters of the three theoretical distributions. The type V Pearson distribution represented the PM10 daily average concentration most closely. However, the parent distributions sometimes diverged in predicting a high PM10 concentration and therefore asymptotic distributions of extreme values were used to fit the high PM10 concentration distribution more correctly. This method can successfully predict the return period and exceedances over a critical concentration in succeeding years. The estimated emission source reduction of PM10 to meet the assigned standard varied from 53% to 63% in the Belgrade urban area. The results provide useful information for air quality management and could be used to examine the similarities and differences among air pollution types in diverse areas.  相似文献   

4.
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5.
利用WRF模式与多尺度空气质量模式(CMAQ)系统模拟了试验期间(2005年1月30-2月2日)兰州市城区SO2的地面浓度,并根据模拟结果进一步分析了兰州市冬季污染物的空间分布特征。研究结果表明西固区和城关区各有一处污染物高浓度区域;受排放源空间分布和气象场的综合影响,夜间SO2地面污染范围小于日间,夜间污染物地面最大浓度明显高于日间,夜间模拟区域平均值低于日间;水平流场和山谷风环流形成的垂直运动均对污染物地面浓度有明显影响。  相似文献   

6.
选取沈阳市区9个典型的大气污染源冬季的PM10排放浓度资料,利用MM5耦合CALPUFF对2007年12月至2008年2月沈阳城市区域气象场和排放PM10浓度分布进行月平均数值模拟.结果表明:冬季沈阳地区受高压控制,北风较强,并经过增强、减弱的过程,多呈现对大气污染物扩散不利的天气形势.高空为偏西风且风速较大时,地面和...  相似文献   

7.
We call attention to the likely importance of the potential reaction OH+ClOHCl+O2. It may only be a minor channel for the reaction of OH with ClO, which is often ignored in models, but if it occurs it considerably increases the rate of recovery of HCl after an air parcel has encountered a polar stratospheric cloud (PSC). The net effect of this reaction on the ozone concentration depends on the relative HCl concentration and whether the air parcel is in a PSC. When an air parcel is in a PSC and the HCl concentration is less than the sum of the HOCl and ClONO2 concentrations, heterogeneous ClO x production is rate limited by the production of HCl. Under these conditions the reaction allows HCl to be reprocessed more rapidly by the heterogeneous reactions of HCl with HOCl and ClONO2. This allows high ClO x concentration to be maintained for longer, and at a slightly higher level, than would otherwise be possible which in turn leads to more ozone depletion. When there are PSCs but HCl is in excess, or outside of the PSC regions (i.e. during the recovery phase), the reaction will always reduce the ClO/HCl ratio and hence slightly reduce the ozone loss.  相似文献   

8.
The dynamical characteristics of concentration fluctuations in a dispersing plume over the energetic and inertial-convective range of scales of turbulent motion are studied using a multiscale analysis technique that is based on an orthonormal wavelet representation. It is shown that the Haar wavelet concentration spectrum is similar to the Fourier concentration spectrum in that both spectra exhibit an extensive inertial-convective subrange spanning about two decades in frequency, with a scaling exponent of -5/3. Analysis of the statistical properties (e.g., fluctuation intensity, skewness, and kurtosis) of the concentration wavelet coefficients (i.e., the concentration discrete detailed signal) suggests that the small scales are always more intermittent than the large scales. The degree of intermittency increases monotonically with decreasing scale within the inertial-convective subrange, reaching a plateau at the very small scales associated with the beginning of the near-dissipation subrange. The probability density function (pdf) of the concentration discrete detailed signal displays stretched exponential tails with an intermittency exponent (tail slope) q that increases as a , where is the scale or dilation and a is a power-law exponent that is dependent on downwind distance, plume height, and stratification strength with typical values in the range from about 0.25 to 0.35. It is shown that the concentration variance cascade process requires a phase coherency of eddies between different scales at the small-scale end of the inertial-convective subrange.The variation of the concentration wavelet statistics with height above the ground is investigated. The increased mean shear near the ground smooths the fine-scale plume structure for scales within the inertial-convective subrange, producing a weaker spatiotemporal intermittency in the concentration field compared to that measured higher up in the plume. The pdf of the concentration detailed signal at a fixed scale possesses less elongated tails with decreasing height z. The intermittency exponent q is found to decrease roughly linearly with increasing z.Finally, the results of the wavelet decomposition are combined to provide a conceptual model of the turbulent transport, stirring, and mixing regimes in a dispersing plume. The implications of the results for contaminant texture in a plume are discussed.  相似文献   

9.
Land surface air temperature (SAT), registered at 1.25–2 m above the ground, is influenced by wind patterns. As a consequence, some phenomena such as urban heat islands and the formation of ground-level air pollutants are affected. Detailed understanding of the effects of wind circulations on SAT is convenient to improve the knowledge of these phenomena. Thus, the joint multifractal analysis has been applied to describe time series recorded at Cordoba (southern Spain) from 2001 to 2008 revealing the presence of seasonal patterns related with warm and cold winds blowing from the SW (later spring and summer) and NE (later autumn and winter), respectively, that provoke different heterogeneity in SAT values. In addition, the extreme high SAT values seem to be related with summer SW winds. However, the presence of rare low SAT values produced by NE winds is less relevant.  相似文献   

10.
2019年1月铜仁市发生了中到重度污染过程,本文利用铜仁市城区逐时环境监测资料,高空及地面气象观测资料,分析了本次污染过程气象条件特征。结果表明,此次首要污染物为细颗粒物（PM2.5）。污染天气发生时,铜仁上空是高压脊或一致的西南气流,地面为冷高压或均压区控制,气压梯度小,风小;当转为高空槽前,地面有冷空气补充,气压梯度增大时,污染物浓度得到降低。同时风速和相对湿度大小跟污染物浓度也有一定关系,地面风速小,空气干燥时,污染物浓度增加;相反,风速增大达4m/s以上,空气相对湿度增大达90%以上,特别是明显的雨雪天气发生时,污染物浓度得到快速降低。另外,污染天气伴随有近地层逆温层持续影响,逆温层厚度越厚,且逆温强度越强,抑制了大气垂直方向的湍流交换,有利于污染物浓度累积增长。受梵净山地形阻挡作用,当近地层为弱偏东风影响时,污染物不能翻越梵净山向西扩散,会在山的东侧堆积,导致铜仁城区污染物在本地循环累积,污染浓度维持较大值。上述研究结果,可为铜仁市空气质量预报及污染防控提供新的参考依据。  相似文献   

11.
Summary The purpose of this paper is to examine some meteorological aspects of air pollution in the Athens area, Greece. Over recent years much attention has been directed to the importance of spells of weather in providing conditions that give rise to inversion of temperature at or near ground level, and hence to risks of severe incidents of air pollution. So, emphasis is given to the importance of anticyclonic conditions, associated with pronounced stability during ground level radiation inversions, when the same sampling sites show high concentration of both SO2 and smoke. Fifteen years of surface and radiosonde data obtained from Hellinikon Airport Athens are used for a climatological base. The meteorology of high concentration episodes has also been examined and the synoptic characteristics for the onset and end of such episodes have been identified. Finally, trends of pollution episodes and calculation of an air stagnation index for Athens have been obtained, which give a predicting indication about the occurrence of high pollution concentration.With 11 Figures  相似文献   

12.
Results from two independently developed biomass-burning smoke plume models are compared. Model results were obtained for the temporal evolution of two nascent smoke plumes originating from significantly different fire environments (an Alaskan boreal forest and an African savanna). The two smoke plume models differed by 1%–10% for [O3], with similar differences for NO x and formaldehyde (relative percent differences). Smaller intermodel differences were observed for the African savanna smoke plume as compared to the plume from the Alaskan boreal fire. Mechanistic differences between the models are heightened for the Alaskan smoke plume due to the higher VOC emission ratios as compared to the African savanna fire. The largest deviations result from the differences in oxidative photochemical mechanisms, with a smaller contribution attributable to the calculation of photolysis frequencies. The differences between the two smoke plume models are significantly smaller than the uncertainties of available photokinetic data or field measurements. Model accuracy depends most significantly on having the fullest possible VOC data, a requirement that is constrained by currently available instrumentation.  相似文献   

13.
A meandering plume model that explicitly incorporates the effects of small-scale structure in the instantaneous plume has been formulated. The model requires the specification of two physically based input parameters; namely, the meander ratio,M, which is dependent on the ratio of the meandering plume dispersion to the instantaneous relative plume dispersion and, a relative in-plume fluctuation measure,k, that is related inversely to the fluctuation intensity in relative coordinates. Simple analytical expressions for crosswind profiles of the higher moments (including the important shape parameters such as fluctuation intensity, skewness, and kurtosis) and for the concentration pdf have been derived from the model. The model has been tested against some field data sets, indicating that it can reproduce many key aspects of the observed behavior of concentration fluctuations, particularly with respect to modeling the change in shape of the concentration pdf in the crosswind direction.List of Symbols C Mean concentration in absolute coordinates - C r Mean concentration in relative coordinates - C0 Centerline mean concentration in absolute coordinates - C r,0 Centerline mean concentration in relative coordinates - f Probability density function of concentration in absolute coordinates - f c Probability density function of plume centroid position - f r Probability density function of concentration in relative coordinates - i Absolute concentration fluctuation intensity (standard deviation to mean ratio) - i r Relative concentration fluctuation intensity (standard deviation to mean ratio) - k Relative in-plume fluctuation measure:k=1/i r 2 - K Concentration fluctuation kurtosis - M Meander ratio of meandering plume variance to relative plume variance - S Concentration fluctuation skewness - x Downwind distance from source - y Crosswind distance from mean-plume centerline - z Vertical distance above ground - Instantaneous (random) concentration - Crosswind dispersion ofnth concentration moment about zero - ny Mean-plume crosswind (absolute) dispersion - y Plume centroid (meandering) dispersion in crosswind direction - y,c Instantaneous plume crosswind (relative) dispersion - Normalized mean concentration in absolute coordinates:C/C 0 - Particular value taken on by instantaneous concentration,   相似文献   

14.
地面观测提供空间点的浓度信息,三维化学模式提供网格面的浓度信息,两者在进行对比验证或同化融合时会因为空间尺度不匹配引入误差,即观测代表性误差。本研究将大气污染地面国控监测站与区县监测站结合起来,获得了京津冀地区高密度地面观测数据,利用该数据首次对京津冀地区6项常规大气污染物（PM2.5、PM10、SO2、NO2、CO和O3）的地面观测代表性误差进行了客观估计,并与Elbern et al.（2007）方法估计的代表性误差进行了对比。结果发现:两种方法对京津冀地区NO2地面观测代表性误差估计非常接近,但Elbern et al.（2007）方法显著低估了SO2、CO和O3地面观测的代表性误差。在此基础上,我们对Elbern et al.（2007）方法及其误差特征参数进行了本地化修正,并增加了PM2.5和PM10的代表性误差特征参数,建立了京津冀大气污染地面观测代表性误差的客观估计方法。  相似文献   

15.
PM2.5污染仍然是湖北省冬季大气污染的首要污染类型,且具有明显区域传输特征,重污染过程的空气污染气象条件有别于华北地区,值得关注。采用WRF/Chem不同排放情景下的模拟结果,并结合观测分析,研究了2015年12月—2016年1月湖北省PM2.5重污染过程的气象输送条件及日变化特征,从大尺度输送条件和局地边界层动力作用分析了外来污染物水平传输、悬浮聚集和向下传输的过程,并解释了该地区观测到的午后PM2.5浓度特殊峰值的气象成因。结果表明,湖北重污染爆发以区域传输为主,地面观测PM2.5极值对应10 m风速可达8—10 m/s,边界层0—1 km为较强偏北风输送,污染传输通量极值位于400 m高度附近,为重要传输通道,低空无明显逆温,重污染过程具有“非静稳”边界层气象特征。重污染形成的大尺度输送条件为,长江中下游及北部地区偏北风异常偏强,南部地区风速减缓,使污染物在中游平原堆积,鄂北边界风速越大,越有利污染输送增长。传输性污染主要来自偏北和东北方向的污染源输送,潜在源区贡献主要为途经偏北通道上的豫中、南阳盆地和关中地区,以及途经东北通道上的鲁、皖、苏等部分地区。PM2.5浓度日变化双峰结构的天气成因不同,21—24时（北京时）峰值为静稳性污染,11—14时峰值为传输性污染。污染输送受大气边界层高度影响,日出前大气边界层高度较低,层结稳定并伴有上升运行,使得低空外来输送悬浮聚集在400 m高度附近;日出后随大气边界层高度升高,静稳层结被破坏,在干沉降作用下高浓度PM2.5开始向下传输,并在午后地面形成峰值。   相似文献   

16.
对防城港市影响最大的首要空气污染物为PM2.5和O3,空气污染日主要集中在秋冬季。空气污染按500 hPa环流形势可分为西北气流型、偏西气流型及西南气流型;按地面气压场可分为冷高压脊型、均压型、高压后部低压前部型。在无境外输入的情况下,PM2.5产生在风速小、气温较低、能见度小、湿度较大并且无降雨或降雨不明显的天气环境里,而O3产生在高温、低湿、日照充足、风速较大和能见度好的天气环境里。在垂直运动方面,中低层的下沉气流利于空气污染物累积。在温度层结分布方面,700~850 hPa的低层存在的逆温层对PM2.5浓度增加非常重要,近地面的逆温层对PM2.5浓度增加的作用要比低层弱,而近地面的逆温层对O3浓度的增加非常重要,但是低层的逆温却不重要。  相似文献   

17.
The CHIMERE mesoscale chemistry transport model is used for the quantitative assessment of the contribution of transboundary transport of anthropogenic admixtures from China to the surface concentrations of major suspended pollutants, aerosol PM10, ozone O3, and nitrogen oxides NOx in the Far Eastern region. Analyzed in detail are the time series of concentration of mentioned substances computed with the model taking account and not taking account of anthropogenic emissions in China. It is revealed that the transboundary transport of anthropogenic pollutants can cause the recurring episodes of manyfold increase in the concentration of PM10 in the south of Khabarovsk region, as well as more rare variations of O3 and NOx concentration. The trajectory and synoptic analysis demonstrated that the episodes of the increase in the concentration of PM10 and O3 in the south of the region mainly depend on the carryover of air masses from northeastern China in the front part of continental cyclones.  相似文献   

18.
Summary  In the central region of Taiwan, ozone episodes occur most often during autumn. Two field experiments were conducted during the autumns of 1998 and 1999 to analyze the vertical profile of the boundary layer and determine its effects on ozone concentration over the region. The vertical virtual potential temperature and wind profiles were derived from tethersonde data. The NOx, NMHC and O3 concentration vertical profiles were monitored up to a height of 500 meters using black-covered Teflon tedler sampling bags. During the experimental periods, nighttime terrestrial long wave radiation could cause the inversion height to reach 500 meters by the following morning. It was shown that these types of synoptic structures suppress the vertical diffusion of NOx, NMHC and O3. During the daytime, measurements indicate that pollutants were well mixed in the upper portion of the mixing layer. At night, the ground level ozone concentration was on the decrease but increased with altitude to a height of 500 m. The NOx decreased with altitude whereas the NMHC showed no significant variations. Received April 13, 2000 Revised July 24, 2000  相似文献   

19.
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（NOy）的分析表明,其主要组分是NOx（80%）,其次是硝酸（HNO3）（<10%）.O3的空间分布与NOy和NOx非常相似.HCHO等其他氧化产物的分布与NOx相似,这很可能是由于在高NOx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.  相似文献   

20.
Results are presented from an experimental investigation of turbulent dispersion of a saline plume of large Schmidt number (Sc=830) in a turbulent boundary-layer shear flow simulated in a laboratory water channel. The dispersion measurements are obtained in a neutrally buoyant plume from an elevated point source over a range of downstream distances, where both plume meandering and fine-structure variations in the instantaneous plume are important. High-resolution measurements of the scalar fluctuations in the plume are made with a rake of conductivity probes from which probability distributions of concentration at various points throught the plume are extracted from the time series.Seven candidate probability distributions were tested, namely, the exponential, lognormal, clipped normal, gamma, Weibull, conjugate beta, andK-distributions. Using the measured values of the conditional mean concentration, , and the conditional fluctuation intensity,i p , the Weibull distribution provided the best match to the skewness and kurtosis over all downstream fetches. The skewness and kurtosis were always overpredicted by the lognormal probability density function (pdf), and underpredicted by the gamma pdf. The conjugate beta distribution for which the model parameters are determined using a method of moments based on the fluctuation intensity,i p , and skewness,S p , was capable of modeling the distribution of scalar concentration over a wide range of positions in the plume.  相似文献   

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