【作者】 王颖；

【导师】 张镭；

【作者基本信息】 兰州大学 ， 大气物理学与大气环境， 2010， 博士

【摘要】 本文在对兰州市西固区2005年1月20日—2月2日大气边界层实验观测资料和空气质量监测资料分析的基础上,利用中尺度气象模式WRF (Weather Research and Forecasting)和空气质量模式Models3系统,对实验期间兰州市西固区冬季边界层低空气象要素特征和空气污染分布进行了模拟；通过与同期观测的气象资料和空气质量监测资料进行对比,了解WRF模式中不同边界层参数化方案对兰州市复杂下垫面边界层低层气象场特征的模拟能力,进而探讨WRF模式不同PBL (Planetary Boundary Layer)参数化方案模拟的近地层气象场对空气质量模拟效果的差异；论文也验证了CMAQ (Community Multiscale Air Quality)模式在复杂地形高分辨率下对污染物输送扩散特征的模拟能力,研究结论对于改进复杂下垫面空气质量数值模拟效果,进而提高空气污染数值预报水平有一定的参考价值；利用模拟结果进一步研究了兰州市冬季污染物的时空分布特征,讨论了大气中各种物理化学过程对SO2和NO2地面浓度的贡献；通过设计敏感性试验,研究了兰州市高架源排放对兰州城区空气质量的影响程度,为治理兰州地区大气污染、改善兰州地区空气质量提供科学依据。论文主要结论如下：(1)WRF中YSU、MYJ和ACM2三种边界层参数化方案模拟的兰州地区冬季温度场空间分布特征相似,但MYJ方案模拟的夜间温度低于YSU和ACM2方案,日间则高于YSU和ACM2方案。这主要是由于局地闭合的MYJ方案湍流交换能力较弱,从而导致地面温度变化幅度低于非局地闭合方案。日间太阳短波辐射增强,湍流混合加剧的结果使得三个方案模拟的地面温度的水平梯度小于夜间。(2)不同边界层参数化方案对地面温度的模拟比较分析表明,对于冬季稳定边界层,WRF模式局地闭合的MYJ方案可以更好地模拟低层温度的时间变化特征。(3)与实测位温廓线对比可知,WRF模式三种边界层参数化方案模拟的夜间位温廓线均较好,ACM2方案模拟的日间低层位温廓线优于MYJ和YSU方案,而MYJ方案对边界层中上部位温廓线的模拟更接近于实测。(4)WRF模式不同PBL参数化方案与CMAQ模式模拟的SO2和NO2日均浓度均能反映出污染物时空分布特征,说明高分辨率的CMAQ模式能够研究复杂下垫面条件下的空气污染问题。(5)不同方案模拟结果表明：ACM2方案与CMAQ模式相结合模拟的污染物浓度与监测值相关性最好,模拟的SO2和NO2日均浓度与监测值浓度的相关系数分别为0.61和0.57；这是由于局地与非局地闭合的ACM2方案描述的湍流扩散特征更接近于实际大气,且气象模式与空气质量模式采用相同的湍流交换系数计算方法,因而模拟效果相对较好。(6)粗粒子排放源的不确定性导致模式对PM1o的浓度模拟效果相对不理想,但模拟的PM25浓度与TSP浓度具有一定的相关性(ACM2方案相关系数达0.398),说明CMAQ模式的化学传输模块可以反映污染物气相化学过程；CMAQ模式具有模拟细粒子在大气中的形成、转化及清除机制的能力,而对粗粒子在大气中形成转化机制的处理能力尚需进一步验证。(7)对模拟的兰州市城区的SO2、N02和PM2.5等主要污染物水平和垂直分布特征分析表明：受排放源的空间分布和气象场共同影响,污染物浓度的高值区分别在城关区的铁路局附近和西固区的兰化宾馆附近；污染物的浓度随高度线性减小,日间湍流混合能力增强,使得日间污染物浓度随高度递减率小于夜间。(8)高架源排放敏感性试验表明：试验期间高架源(有效源高H≥100m)排放的SO2和NO2分别占污染物排放总量的59%和72%；由高架源排放造成的SO2和NO2地面浓度日均值对兰州市主城区的贡献率分别为46%和49%；可见高架源排放对兰州市空气质量影响较大,控制高架排放量是治理兰州市大气污染的有效途径之一(9) CMAQ过程分析模块分析表明：对于SO2地面浓度,污染源排放的影响最大,其次是垂直扩散过程的影响；而对于NO2地面浓度,化学反应过程的影响最大,其次是污染源排放,这也是各种物理化学过程对NO2地面浓度的影响区别于SO2的主要特征。更多还原

【Abstract】 The mesoscale weather model WRF and CMAQ model were used to simulate the characteristics of meteorological field and air polluted distributions in Xigu district of Lanzhou city in winter from the 27th of January to the 2nd of February in 2005, which are based on the analysis of atmospheric boundary-later observed and air quality monitoring. The capacities of WRF and CMAQ models over complex terrain were testified by comparing simulated results and observed data, the effects of meteorological fields from three PBL (Planetary Boundary Layer) schemes (YSU, MYJ and ACM2) on the simulated results of CMAQ model were discussed; The differences of three PBL schemes (YSU, MYJ and ACM2) on the retrieve of meteorological characteristics in lower layer were analyzed, the effects of meteorological fields from three PBL schemes on the simulated results of CMAQ model were also discussed. The results can improve the accuracy of numerical simulation and air pollution forecasting in Lanzhou city. The spatial and temporal distributions of air pollutants in Lanzhou city were also investigated by analyzing the contribution of the various physical-chemical processes on the concentration of SO2 and NO2; some sensitive numerical experiments were used to study the effects of higher emission sources on air quality in Lanzhou city. This would provide some scientific foundations for controlling air pollution and improve air quality in Lanzhou city.(1) Comparing the results of the observations and simulations shows that the metrological variables have similar characters in PBL with three PBL schemes in WRF, but the temperature from MYJ scheme was lower than that from the other two schemes during the night, with opposite results during the daytime, which is caused by stronger turbulence due to the short-wave radiation during the daytime.(2) Local closed MYJ parameterization presents more reasonable daily changes on surface temperature than the other non-local closed parameterizations (YSU and ACM2) due to the facts that traces and energy were dominated by local turbulence, which results in the weak turbulent transportation in winter stable condition especially in valley city.(3)Investigating observed and simulated profiles of the mean temperature shows that three PBL schemes have good characters during the night, while the temperature profiles simulated by ACM2 (combined with local and non-local scheme) PBL scheme in WRF in is better lower layers than that from the other schemes during the daytime. It also presents that MYJ gives more reasonable results in upper layer. (4) Spatial and temporal characters of pollutants were well simulated by WRF model combined with CAMQ model with different PBL parameterization, which also testified the capacity of studying pollutant problems by CMAQ model.(5) The simulated concentrations of air pollution using the ACM2 PBL scheme was in WRF model combining with CMAQ model were consistent with the observed data The correlation coefficients of simulated and observed SO2 and NO2 daily averaged concentration are 0.61 and 0.57 respectively. It is because that’the turbulent exchanges are well simulated by ACM2 PBL scheme. The same exchange coefficients adopted by air quality model and meteorology model is another reason.(6) The simulated PM10 concentration was not satisfied due to the uncertainty of course particles. Simulated PM2.5 concentration may be related to TSP concentration, which indicates that the chemical transport process in CMAQ model can illustrate the formation, change and clarity of fine particles, which must be tested for the coarse particles.(7) The horizontal and vertical distributions of SO2, NO2 and PM2.5 in Lanzhou city show that they are affected by the spatial distribution of emission sources and meteorological fields. There are two maximum concentrations of pollutions in Lanzhou, which located around Tieluju in Chengguan district and Lanhua hotel in Xigu district. Pollutant concentration decreases linearly with height. The vertical gradients of the concentration are smaller during daytime than that in night because of the stronger turbulent mixing in the daytime.(8) The results of sensitive experiments of the emissions of higher emission sources show that:SO2 and NO2 emissions of higher emission sources accounts for 59% and 72% in total emissions; and SO2 and NO2 concentration caused by higher emission sources accounts for 46% and 49% in daily averaged concentration. Controlling the emissions of higher emission sources is the effective method to control air pollution in Lanzhou city.(9) Analysis on physical and chemical processes of different pollutions shows that pollution emission is the main factor over effecting SO2 surface concentration, and the vertical diffusion is the secondly one, while chemical processes have significant effects on NO2 concentration.更多还原