| The environment of human subsistence has a close relation with atmospheric boundary layer processes. Since 20's century, for the development of industry and traffic, especially for the quicken-up of urban trend, the characteristics of urban boundary layer (UBL) become more and more complex. Due to its too many impact factors, it is very difficult to recognize the mechanism of physical and chemical processes of UBL. So in order to protect the environment of human subsistence and set up a benign circulation structure of urban environment to control urban air pollution, study on UBL air dynamical structure characteristics and their coupling mechanism with chemical process has became an exigent project that will effect the development of society and economy. As our capital, Beijing's urban environment problem is more important and noticeable. By utilizing vertical observational data of "BECAPEX" (Beijing City Air Pollution Observation field experiment), including 15 levels gradient data, 3 levels ultra-sonic data, tethersonde profiler data and so on, the integrated studies on Beijing UBL processes vertical structure features are carried out. Characteristics of Beijing UBL turbulent vertical structure and its difference with other cities and underlying surface are disclosed. The UBL vertical dynamical structure characteristics especially its turbulent vertical structure features and their relations with pollutant concentration during different urban catastrophic events as sand/dust weather and city fog process are studied. Meanwhile, by amending aerodynamic parameters in numerical model, the simulation capacity of it is improved. Furthermore, the effects of change in urban underlying surface on UBL dynamical, thermal and turbulent structure are investigated. So the basic turbulence dynamical pattern of Beijing UBL is disclosed through all above studies. The main conclusions are as follows:(1) Integrated studies on turbulence vertical structure of Beijing UBL suggest: Under unstable condition, the normalized turbulent wind standard deviation (σ_u/μ*σ_v/μ* σ_w/μ* ) and turbulent temperature standard deviation (σ_T/T*)at height of 47 and 120m follow the Monin-Obukhov similarity theory and its normalized function are given out as well. But data at height of 280m is scattered and does not follow the M-0 theory. At day time the near surface layer includes heights of 47 and 120m while 280m has beyond it. Under stable condition, according to the value of dimensionless stability parameter (z' /L), the stable near surface layer of 47m could be divided into two regions. When z'/L<0.1 it is weak stable region where the M-0 similarity theory can be applicable. The other is strong stable region when z '/L>0.1. In this region the normalized turbulent wind standard deviation increase with stability but the normalized turbulent temperature standard deviation remain constant and thesimilarity theory can not be applied. And this phenomenon can not be found at height of 47 and 120m at stable condition.(2) At all height of Beijing UBL, comparison of normalized turbulent wind standard deviation in different direction show that the value of σ_u/μ* is largest, then it is σ_v/μ*, σ_w/μ* is the smallest. As to vertical direction, σ_u/μ* increase as height increase. To σ_v/μ* and σ_w/μ*, their values at 47 and 120m are very close while the value at 280m is larger than that two layers. The urban underlying surface leads to the decreased normalized turbulent wind standard deviation but increased turbulent intensity in near surface of Beijing. And the impact is more remarkable in horizontal direction then in vertical direction.(3) The drag coefficient (Co) of Beijing underlying surface increases as z'/L increases but decreases as height increases. Under near-neutral condition, C_D at the height of 47m is between 0.1-1, for 120m it is 0.01-0.1, and for 280m it is 0.001-0.1 and centered near 0.01. Compared to that of the different underlying surface, C_D in near surface of Beijing has increased considerably.(4) The particle air... |
PDF Full Text Request