【作者】 刘晓环；

【导师】 王文兴；

【作者基本信息】 山东大学 ， 环境科学， 2010， 博士

【摘要】 近年来,我国高速的经济发展和城市化进程加速了大气环境的恶化,高浓度的大气污染物严重危害人体健康并破坏生态环境。因此,控制大气污染物排放、改善空气质量已成为我国面临的一个非常严峻的环境问题。本研究旨在通过空气质量模型的模拟,分析我国主要大气污染物浓度的时空分布现状,探讨几个代表性城市和地区污染物的形成过程,以期为国家区域大气污染控制对策提供理论基础。本论文利用美国环保局第三代空气质量模型Models-3/CMAQ(4.7版本)对我国主要污染物(PM10、O3、SO2和NO2)浓度进行了数值模拟。主要分析了这些污染物浓度的时空分布以及冷锋天气系统对颗粒物浓度的影响。另外,还根据过程分析模块(综合过程速率和综合反应速率)的结果分析了臭氧和二次无机颗粒物分别对其前体物(VOCs, NOx、SO2和NH3)敏感性、定量地分析了不同的大气物理-化学过程(大气水平输送、垂直输送、气溶胶化学过程、云雾和湿沉降过程、干沉降等)对代表性地区颗粒物和臭氧的形成过程的影响。模拟结果与地面观测和卫星数据的对比表明,本论文模拟结果存在一定的偏差,但是基本能够满足后续情景分析、敏感性分析和过程分析的要求。从CMAQ模拟结果看出,我国PM10、SO2和NO2浓度的空间分布在地理上存在相似性,四个季节均呈现东高西低的空间分布特点,高浓度区主要包括京津冀、长三角、珠三角和四川盆地。受气象条件和源排放量季节变化等因素的影响,三种污染物种浓度一般在冬季最高,夏季最低。臭氧的时空分布与PM10、SO2和NO2不同,臭氧浓度(1小时最大值,>70ppb)最大值出现在夏季,主要位于我国华北地区。春季,长江以北～30°N-42°N之间有一条臭氧高浓度带贯穿我国东西,该区域臭氧(1小时最大值)浓度范围约60-70 ppb之间,其他地区臭氧浓度约55-65 ppb。冬季由于太阳辐射较弱,臭氧浓度较低,全国大部分地区臭氧浓度在50ppb以下,冬季臭氧浓度较高的地区出现在青藏高原,约50～60 ppb。冷锋天气过程对PM10浓度影响的模拟个例的研究表明,本次模拟很好的捕捉到这次冷锋天气过程,冷锋“间歇期”是污染物浓度逐渐积累的时间,冷锋过后,颗粒物浓度明显降低。臭氧生成敏感性分析表明,冬季我国中东部广大地区(东北地区、华北平原、长江三角洲和珠江三角洲等)和西部的几个城市大气臭氧生成主要受VOCs控制,西部地区除几个城市外其他地区臭氧生成受NOx控制。夏季臭氧生成VOCs控制区的范围比冬季大大缩小,仅分布在我国几个大城市地区(如北京、上海等),其他地区臭氧生成主要对NOx敏感。从北京和上海市区、郊区小坪和瓦里关大气背景站这几个不同地区大气中HOx自由基收支循环分析也可看出,城市和郊区大气HOx自由基循环过程存在差异,不同的自由基循环终止反应证明夏季北京、上海市区臭氧生成对VOCs敏感,小坪和瓦里关臭氧生成对NOx敏感。颗粒物生成敏感性分析得出,夏季颗粒物质量浓度对SO2敏感性最强,其次为NOx和NH3。对夏季SO2、NOx、AVOCs以及NH3排放量削减的情景模拟结果表明,除了颗粒物的一次源排放之外,S02源排放削减比NOx和NH3削减可以更有效控制颗粒物质量浓度。城市地区夏季臭氧污染可以AVOCs控制排放为主。但是若通过SO2和NOx减排控制城市地区颗粒物污染,则会引起臭氧浓度的升高。从臭氧和颗粒物生成敏感性分析与情景模拟的结论可见,在我国臭氧和颗粒物污染都比较严重的情况下,通过控制污染源排放同时降低臭氧和颗粒物污染、改善空气质量会受到较多因素限制,因此污染物排放控制措施的制定需考虑不同地区在不同时间下的具体特点。北京市区夏季近地面大气臭氧昼夜浓度差大于高层大气臭氧昼夜浓度差,臭氧夜间易在高层贮存,对次日日间臭氧浓度造成影响。边界层内臭氧大气化学过程在垂直方向存在差异,臭氧生成高值区在200-1500 m之间。近地层臭氧浓度升高主要依赖边界层内高层大气臭氧的垂直输送。干沉降是近地面大气臭氧去除的重要途径之一,另外近地面臭氧还因与NO反应而被消耗。相对于近地层和几百米高,1500 m之上大气臭氧浓度受光化学影响减弱。一次颗粒物排放对北京市夏季低层大气(」～300 m)的PM10质量浓度的影响大于高层大气。气溶胶化学过程对PMlo质量浓度的影响有正有负：负贡献主要包括低层大气中硝酸盐的分解等过程,正贡献包括大气中硫酸盐、硝酸盐以及二次气溶胶等新粒子的生成、H2SO4和HN03在已经存在粒子上的凝结等。干、湿沉降对颗粒物去除有重要的作用,干沉降对颗粒物的去除作用多发生在近地面。大尺度的水平传输可降低北京市颗粒物浓度,而垂直传输在不同高度不同时间对颗粒物质量浓度的影响不同。更多还原

【Abstract】 During the past several decades, rapid economic development and urbanization process led to deterioration of air quality in China. High concentrations of air pollutants caused serious risk to human health and ecological environment damage. Therefore, it is urgent to improve air quality through reducing emission in China. The primary objectives of this study are to evaluate seasonal characteristics of major pollutants and to understand formation mechanisms of major air pollutants in China via air quality model simulation. Such information would provide useful perspectives for developing local and regional emission control strategies.Models-3/CMAQ v4.7 was applied to simulate the concentrations of the major pollutants (PM10, O3, SO2 and NO2) in China. Temporal and spatial distributions of these pollutants and the impact of cold front weather system on PM10 concentrations were investigated. Process analysis (PA) in CMAQ (including integrated process analysis (IPR) and integrated reaction rate analysis (IRR)) were used to identify the most influential processes and chemical reactions (such as horizontal/vertical transport, aerosol processes, clouds/fog processes and wet/dry deposition) that led to the accumulation or loss of O3 and PM10 in atmosphere. Secondary inorganic aerosol and O3 chemistry regime analysis were also analyzed based on the CMAQ-PA results. Model evaluation results indicated that our simulated results were acceptable and could fulfill the need of air quality impact and control scenario analysis, O3 and PM chemistry regime analysis and process analysis.CMAQ simulations showed that higher concentrations of SO2, NO2, and PM10 occurred over Jing-Jin-Ji Bohai sea rim region, Yangtze River Delta (YRD) area, Pearl River Delta (PRD) area and Sichuan Basin. Highest surface concentrations of SO2, NO2, and PM10 were found in winter and lowest in Jul due to the variations of weather condition and pollutants emissions. Temporal and spatial variations of O3 concentrations were different from SO2, NO2, and PM10. Highest 1-h O3 concentrations (>70 ppb) were found over North China Plain in summer. April also had relatively high O3 mixing ratios of about 60-70 ppb over large areas in the North of Yangzi River (～30°N-42°N), which extended from east to west of China while 55-65 ppb over most other areas. Compared with other seasons, Jan had the lowest O3 mixing ratios (<50 ppb) over most area of China due to weaker solar radiation in winter, except Tibetan Plateau in the western part of China (O3 mixing ratios were 50-60 ppb). Case study of PM10 concentrations influenced by cold front system indicated that our simulation captured this cold front weather system and cold front weather system could reduce PM10 concentrations significantly.Indicator analysis of O3 chemistry regime indicated that VOC-limited chemistry covered the central and eastern China including the North China Plain, YRD, PRD and the northeastern China, as well as some major cities in most provinces, while other areas were NOx-limited O3 chemistry in winter. NOx-limited O3 chemistry dominated over almost entire China during summer except several metropolitan areas (such as Beijing and Shanghai). Differences between HOx radical termination reactions in urban and rural areas also indicated VOCs-limited chemistry over Beijing and Shanghai, and NOx-limited chemistry at Xiaoping and Waliguan sites. Indicator analysis of PM chemistry regime suggested that PM formation was more sensitive to SO2 reduction than NOx and NH3. Scenario analysis indicated that SO2 control would be more effective to PM10 reduction than NOx and NH3 besides primary emissions of PM10. AVOCs reduction could lead to O3 reduction over metropolitan areas in summer while NOx reduction could lead to O3 reduction over rest areas. However, if SO2 and NOx reduction were used to control aerosol pollution over metropolitan areas, O3 mixing ratios will increase. These results indicated that different emission control strategies for air quality improvement (separate NOx or VOC emission control, or integrated control of NOx and VOCs emissions) should be taken over different regions and during different seasons to effectively control ambient O3 and PM10 air pollution.Diurnal variations of O3 concentrations in Beijing at surface layer were larger than that at higher altitude, indicating that O3 stored at higher layers at nighttime and contributed to the O3 mixing ratios of next day. Obvious discrepancy of O3 formation processes existed between surface layer and upper level. Highest O3 production rate was found at 200-1500 m layer, and vertical transport was the dominate factor that contributed to O3 accumulation at surface layer. O3 reaction with NO and dry deposition process were two major factors that contributed to O3 loss at surface layer. Above 1500 m, gas-phase chemistry contributed much less to O3 formation compared with lower layers.Primary particulate species mainly contributed to PM10 increase at low layers (< 300 m). Aerosol processes had positive and negative contributions to PM10 concentrations, e.g. the positive contributions included the formation of sulfate, nitrate, second organic aerosol, the condensation of gas phase H2SO4 and HNO3 on pre-existing particles, while the negative contribution was due to the thermal decomposition of nitrate. Wet and dry deposition processes were two main sinks of PM10, and dry deposition only occurred at surface layer. Horizontal transport helped transport particles from heavily-polluted areas to downwind areas. Vertical transport contributions to PM10 concentrations changed with layers.更多还原