Potential source area (footprint) related to air pollution of Beijing is investigated. Long-term modeling of meteorological fields is carried out by WRF model, from 2000 to 2014. A backward dispersion footprint model is used to derive hourly footprint using these meteorological data. Long-term mean source area is obtained as well as its seasonal variation. Heavy air pollution episodes in winter and autumn are selected from air pollution index (API) data in the period from 2000 to 2012. Relationship between air pollution and its potential source area is discussed. Results show that daily mean footprint varies both by its pattern and direction, indicating strong temporal variation of the source areas for Beijing. Long-term mean source area for Beijing is shaped like a triangle, and the southwest branch is the strongest, the other two are in the east and north. Beijing locates in the middle to norther position of the triangle. Seasonal variation of the mean source area show enhancement in the southwest and south in summer (July) and autumn (October). Local wind frequency may mislead assessment of source area, in comparison to the footprint derived by the backward dispersion model. By handling all dispersion processes, such as accumulation of air borne materials, the footprint model provides reasonable information of source area. Mean footprint of all heavy air pollution episodes reveals that a wide arc zone in front of the mountains is the most significant source area to air pollution of Beijing. This zone starts approximately from Shijiazhuang in the southwest to Beijing, and then turning to Tangshan in the east.

 Based on the surface data of NCDC (National Climatic Data Center), the wind data of 345 stations during 1985 to 2014 are chosen, the characteristics of low wind-speed meteorology and the distribution of low wind-speed’s mean percentage in China are analyzed. Harbin, Urumqi, Beijing and Chengdu are chosen from 345 stations as representative cities, and the characteristics and annual variabilities of low wind-speed’s percentage are studied. The results show that: 1) The probability of occurrence of low wind-speed is about 40% in China during recent 30 years, as for the four representative cities, Harbin is the lowest (25%), Chengdu is the highest (60%); 2) Time-of-day occurrence: during the period of midnight and early morning, the probability of occurrence of low wind-speed is high; 3) Monthly occurrence: from September or October to next year January, the probability of low wind-speed maintains at a high level, the lowest probability happens in April; 4) Persistence, 36% low wind-speed condition can last at least 3 hours in China, in the four cities, 20% low wind-speed conditon can lasts at leat 12 hours in Chengdu; 5) Distribution, the probability of low wind-speed is high in the South and the inland, while it is low in the North and the coastal; 6) Annual variabilities, Harbin has increasing trend, while other three stations’s long-term trend is not obvious.

Based on the data of 460 automatic weather stations in the year of 2006, after quality control and data organization, meteorological field of the whole year was calculated by Calmet model. On the basis of hourly wind field and 72-hour trajectory, the diffusion state of Pearl River Delta (PRD) area was divided into three types (systematic wind field, local atmospheric circulation and feeblish systematic wind field). Based on this classification and further classification of atmospheric transmission trajectories, the characteristics of atmospheric diffusion, and atmospheric transmission trajectories and reach in PRD area were analyzed. Specifically, the characteristics of atmospheric transmission and diffusion of the PRD region obviously change with seasons and are highly influenced by sea-land breeze. The best diffusion condition is in winter while worst in Autumn. Additionally the transmission trajectories are markedly distinct between different types and seasons.

As a significant parameter in atmospheric environmental studies, atmospheric boundary layer height (ABLH) is of great importance in research about pollutants transportation and diffusion, cloud microphysical process, model parameterization and so forth. Based on the WRF modeling in Hainan Island, the temporal and spatial variation of ABLH is analyzed. The results show that, the mean ABLH in the northern part is relatively bigger in spring and summer, about 500?600 m; while in the circular coasts from northwest to east, southeast that is bigger in autumn and winter, about 500?700 m. However, in south central coteaux the mean ABLH keeps a low value of about 200?500 m and variations of differ seasons are very little. There is a good correspondence between prevailing background wind and factors that benefit the sea breeze developing. Mean ABLH in surrounding sea appears such seasonal characteristics low in autumn and winter with a value of 500?800 m but high in spring and summer with that of 100?500 m. The ABLH inland comes to its maximum of above 1800 m in spring and summer but that offshore 1300?1500 m in autumn and winter. The diurnal characteristics inland appears very much like that in typical land surface, while in coastal zone deeply influenced by prevailing wind, the daily variation of atmospheric boundary layer presents maritime characteristics under the circumstances of onshore background wind but terrestrial on occasion of offshore wind.

Based on data from a comprehensive atmospheric dispersion experiment of high temporal and spatial resolution over a complex hilly-valley area in Hunan province, the applicability of USEPA (United States Environmental Protection Agency) recommended guideline model CALPUFF (California Puff Model) in near field over complex terrain was investigated. Using diagnostic wind fields of different temporal resolutions and various dispersion schemes, the near-field concentration distributions under various meteorological conditions were simulated and compared with the observed tracer concentrations. The results show that using the measured turbulence profiles to calculate dispersion parameters can better simulate near-field concentration distributions. The modeling results can be improved if the fitted relationships between standard deviations of turbulent velocities and stability parameters are used instead of the default CALPUFF turbulence parameterization scheme. The modeling results are not sensitive to the temporal resolution of wind fields and dispersion schemes when the wind speed is high and wind direction is steady. However, under low and variable wind conditions, the 10 min wind field is needed to model the ground concentration distributions. The modeling results of measured turbulence scheme are higher than those of similarity scheme and closer to the observed values. Overall, CALPUFF modeling system can well simulate the near-field peak concentrations over this hilly-valley complex terrain by using either the hourly wind field and turbulent measurement or 10 min wind field and modified similarity scheme.

Disturbances of cooling towers on wind and turbulence field were simulated with a computational fluid dynamics model, Fluent. The influence on atmospheric dispersion was simulated by using a Lagrangian stochastic particle model. With 4 cooling towers and 4 emission stacks, and a typical wind speed of 1.5 m/s at a nuclear power station site, flow disturbances under neutral condition were simulated for three wind directions, i.e., ESE, SSE and SW. Dispersion plumes and their standard deviations were calculated for each wind direction and 2 selected stacks. Results show that, in case of wind direction with least disturbance on the air flow, there can be almost no influence of the cooling tower at the dispersion. While with significant influence of the air flow disturbance, the standard deviations of plumes can be increased for 2 and 1 stability classes in horizontal and vertical direction. The influence is mostly significant within 1 km of downwind distance.

Observations of VOCs concentration were conducted at a litchi plantation in the Pearl River Delta in July 2008 and February-March 2009 respectively. VOCs fluxes were estimated based on the relationship of flux-gradient and REA method using the VOCs concentration data. Statistical evidence indicates that the major emission matter is isoprene with a typical daytime mean flux 0.932 nmol/(m2?s) in the growing season over the litchi plantation. While in the non growing season, the flux is negligible. This study provides a reliable reference not only for emission rates for litchi and manmade plantation, but also for usage of micrometeorological methods to measure VOCs fluxes.

In order to systematically study the statistical characters of coastal near-surface wind over the China Sea, a division for wind regions and an automated classification for wind fields were realized through cluster analysis. Four wind regions and 31 wind patterns were obtained. Wind regions show the correlations of wind speed among different parts of the China Sea. Identified wind patterns include the typical wind fields of monsoons, and wind fields reflecting frequently occurring synoptic systems. Wind fields in the transition periods between monsoons and wind fields in the whole year were also identified. Besides mean wind speed, other meteorological factors, including temperature and humidity, are also significantly affected by the patterns. Investigation of occurrence frequencies, timing, mean wind speed and wind direction distribution of wind patterns reveal the statistical characters of coastal near-surface wind over the China Sea.

The dispersion simulations are carried out over a coastal region where Zhangzhou nuclear power station will be located. The diagnostic wind model, trajectory analysis and random walk model are used. The dispersions in this area are determined both by synoptic systems and land-sea breeze circulation. Spatial variation of wind field is not obvious, which leads to the straight dispersion plume. Temporal variation of wind field, particularly the wind direction transition caused by transient of land and sea breezes, plays an important role in atmospheric diffusion. Results from random walk simulations agree well with the in situ tracer experiment data, though quite large scatter still exists in some cases due to the effects by complex terrain and coastal meteorological condition.

Diffusion process of tracer experiments on complex seashore of Sanmen in Zhejiang Province of China is simulated by a combined modeling system. This system is composed of the diagnostic wind model Calmet, which provides a high-resolution wind field, and the Lagrangian random-walk dispersion model RPPM which calculates surface concentration distribution for comparison with the field measurement. In each tracer experiment, tracer concentration is measured at sample stations which spread over several arcs so as to capture the main body of the plume. Comparison between surface concentrations generated by the two methods reveals that the modeling system considerably well simulates the trajectory of the plume and distribution of surface concentration.

A typical stagnant air pollution episode happened during October 1 to 10, 2004 in Beijing. Using the method of footprint analysis and the monitoring data for major pollutant (PM10 in this period, detailed process and the source-area of potential influence in this episode were analyzed. Results illustrate that: 1 the diurnal variation of PM10 concentration differs significantly from usual case, and high concentration appeares in the afternoons and evenings, 2 the horizontal distribution of PM10 concentration has a pattern as “the higher in the south and the lower in the north”, and 3 the development of the episode is accompanied with obviously extending of the footprint 100-200 km to the southwest of Beijing, suggesting that source emission from the southwest may contribute significantly to this heavy pollution episode.

The large aperture scintillometer (LAS) is a versatile instrument to measure area-average heat fluxes over heterogeneous surface. In order to analyze the source area of LAS data, a new Eulerian analytical footprint model is developed. The parameters of the LAS footprint are discussed in detail and some outcome of the model application over a heterogeneous field experiment are shown. The good agreement of the results demonstrates that this footprint model is an effective and practical tool for complex surface study.

The non-hydrostatic mesoscale model ARPS 5.0IHOP5 was used to simulate the background wind field in the atmospheric boundary layer over Beijing-Tianjin area. As a comparison, the wind-field diagnostic analysis with observed meteorological data was used to generate hourly wind field in the lower atmosphere in August 2004. The results show that two mesoscale circulations affect this area, they are sea-land breeze and mountain-valley breeze. The mountain-valley breeze may influence the whole plain area, and the influence of sea-land breeze can reach as far as 100km approximately into the inland. Under the influence of these two circulations, the dominant wind is southerly from afternoon to midnight, and then changes to northerly till forenoon. During the period of switching from southerly to northerly, a belt of convergence occurs in the front of the western mountains in the model domain.

The concept and application of blending height are introduced. Large-eddy simulations were conducted to study the blending height in convective boundary layers over heterogeneously heated surfaces. The influences of heterogeneous length, heterogeneous strength and wind speed on blending height were investigated. The results show that the blending heights are mainly determined by the heterogeneous length and wind speed, while less influenced by the heterogeneous strength. Blending height appears at the height where the spatial standard deviation of heat flux decreases to 5% of that on the surface and can be fitted as Z_b = 1/C_wm * w'θ'_sfc/Θ₀ * L^a_hetero/U^b, with a=1.266, b=0.854, C_wm=3.205×10^-3.

Using air sounding data from 3 stations in the western urban and suburban districts of Beijing in September and October, 2000, the authors study the diurnal variation of the atmosphere boundary layer height, and analyze the vertical structures and characteristics of temperatures, wind directions and wind speeds in the boundary layers. Differences of the variables between urban and suburban districts are compared. The results show that, in the autumn of Beijing, the maximum atmosphere boundary-layer height is about 1km in daytime, and the nocturnal stable boundary layer height is between 200 and 400m. For clear days, daytime temperatures in urban area are higher than those in suburban districts, indicating the effect of urban thermal-island. However, temperature difference at night is not obvious. A lower boundary layer, caused by strong temperature inversion over it, leads to weak vertical exchange between the boundary layer and upper layers. It thus favors the formation of fogs and haze. According to the vertical wind profiles, three types of nocturnal flows below 400m could be identified, they are (i) weak winds in the whole layer; (ii) lower-level jet; and (iii) with maximum of wind speed near surface. All these flows are closely related to different thermal stratifications.

The iterative algorithm for calculating the Monin-Obukhov (M-O) length in the aerodynamic method is transformed into the problem of finding the fixed points of a one-dimension mapping in nonlinear theory. By adopting the nondimensional functions of the profile-flux relationships summarized by Dyer, the analytical solution of M-O length is derived for the stable surface layer, which is applicable to Richardson number (Ri) less than 0.2. The consistence between analytical and iterative solutions is validated through the computations of 4 calculation cases for the stable surface layer in typical summer and winter time. According to the theory of fixed-point stability in nonlinear sciences, the convergence property is discussed. It is concluded that the analytical solutions can be figured out by iteration in principle, though iterative solutions exhibit significant errors when Ri approaches 0.2.

Dispersion of heavy dust-particulate was simulated by means of a Lagran gian stochastic model with turbulence fields of convective boundary layers (CBL) derived from a large-eddy simulation model. Three geostrophic winds of 0.0, 2.0 and 4.0 m•s^-1were used for the CBL simulations. And three gravity falling velocities of 0.2, 0.4 and 0.6 (which corresponded to mineral dust diameters of 53, 80 and 104 μm, respectively) were employed to represent gravity effect of dust particulate. The model results were compared well with previous works of water tank experiments and numerical modelings for neutral particle diffusion. Diffusion of small particle (53μm) behaved in CBL similar to the neutral one, while the large particle (104μm) could hardly be carried to upper part of the CBL. An interesting result was that strong wind in CBL seemed to benefit heavy particle falling to the surface, if other atmospheric conditions kept the same. This phenomenon need to be verified by observation.

Spatial and temporal variation of PM₁₀and SO₂over Beijing area is obtained by analysis of monitoring data in 1999 and 2000. Random walk simulations are carried out to reveal impact of the urban emission to whole simulation domain. Accumulation effect of air pollutants in this area is also discussed. Results show that 1) Spatial distribution of PM₁₀and SO₂concentration is centered to urban area of Beijing and characterized by distinct diurnal and seasonal variation. 2) Diurnal variation of air pollutant concentration in urban area differs o bviously from that in clean station Dingling (background site). The former peaks twice in a day while the latter has a single peak. 3) Conditional statistics of monitoring data with the support of the random walk simulations show evident in fluence of urban emission to the clean station, Dingling. 4) Air pollutants may accumulate essentially over the simulation domain in winter, with a time scale 2-5 days approximately. The advection-diffusion factor plays a crucial role in the local accumulation process of air pollutants.

Large-eddy simulations are carried out for atmospheric boundary layers from con vective to near-neutral cases. The simulation condition covers the range as follows: surface heat flux from 0.0001 to 0.2 K·m·s^-1, geostrophical wind speed from 0～15 m·s^-1, and the correspondent stability parameter -z/L from 0.0062 to 368. Simulation results show that in the atmospheric boundary layer, the heat flux and momentum flux profiles have the form as those in typical unstable condition and near neutral condition. And within the stability situation the model resolves the turbulence in ABL well, in good agreement with observation data, particularly in surface layer. By current resolution, the model does not properly simulate turbulent characters in near neutral boundary layer. While convective roll vortices may emerge in strong wind and weak unstable condition, with the stability range of -z/L from 0.668 to 24.6 approximately.

Spatial distribution and time scales of atmospheric diffusion over Beijing area are revealed by means of a random walk simulation model and practical meteorological data with a specified emission source from the city. Results show a southward transport pattern for wintertime while a northwest transport of pollutants in summer. The area is the least evidently influenced by the emission source in spring, while the largest in autumn.The time spent for instantly emitted material removing from the model domain varies from winter-spring to summer-autumn. The former was shorter one of less than 20 hours; the latter was longer one of approximately 30 hours. Distribution of occurrence probability for different removal times was not symmetry.Reducing slowly at the end of longer removal time, probability exists for pollutants remaining in this area a long time.

Refined grids were utilized in a large-eddy simulation(LES) model for obtaining high-resolution planetary boundary data and analyzing surface layer turbulence. Simulation results showed that refined meshes reduced turbulent contributions of subgrid scales(SGS), sensitivity of simulation results to SGS parameters decreased, and features of the whole boundary layer were explicitly resolved better. Results also revealed flux-profile relationship correctly in surface layer and a good agreement of turbulent velocity characters with observation. Therefore, it concluded that the LES method was able for simulation of surface layer flow and turbulence, and might be used for further applications.

Wind-field diagnostic analysis and historical observation data are used to reveal general flow patterns of lower atmosphere over Beijing area. The preliminary results show that air flows in this area could be classified into autumn-winter pattern and spring-summer pattern. The former is under effect of more strong synoptic systems, while the latter shows more characteristics of mesoscale thermal circulation induced by topography. The mesoscale circulation determines basic air flow patterns in this area, which is typical in spring-summer season and in calm weather of autumn-winter season. Air flow under strong wind condition in autumn-winter season is seriously perturbed by topography. The perturbation displays as a horizontal vortex covering whole city of Beijing and part of mountain area in northwest.

Large-eddy simulations are carried out for the adjustment of convective boundary layer (CBL) over heterogeneous surfaces. Simulations are confined for zero mean-wind and flat terrain. Surface heat-flux is set varying in x-direction with its average to be 0.15K·ms^-1 and varying magnitude 0.05K·ms^-1. Wavelengths or scales of surface heterogeneity are less than 20km. Simulation results show that CBLs do reach a quasi-stationary state correspondent to specified surfaces, after a long enough evolution. In this transition process and after that, horizontal statistics, i.e. mean potential temperature and vertical heat-flux, show profiles little differences to those over homogeneous flat surface. Main effect of surface heterogeneity is to increase kinetic energy in CBL and the increase concentrates in the direction of surface heterogeneity. The time of CBL spent to reach its first peak of mean kinetic energy, t_c, and dimensionless kinetic energy of CBL in its stationary state, E_eq, could be two scales for the adjustment process. Results show that, qualitatively, the larger scale of surface heterogeneity, the higher value of dimensionless kinetic energy E_eqcould be reached, meanwhile the longer transition time t_c is needed.