兰州大学机构库 >大气科学学院
中国西南地区冬季空气污染气象成因的诊断分析和数值模拟研究
Alternative TitleNumerical Simulation and Diagnostic Analysis of Meteorological Causes of Winter Air Pollution over Southwest China
胡钰玲
Thesis Advisor王式功
2019-10-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Degree Discipline气象学
Keyword中国西南地区 四川盆地 空气污染 气象参数 冬季干旱 数值模拟
Abstract空气污染、尤其是污染事件的发生通常由不利于污染物扩散的气象条件和过量的污染物排放共同作用造成的。中国西南地区受复杂地形和高原天气系统的共同影响易形成有别于其它地区的不利大气扩散条件,导致冬季空气污染事件时有发生,其中四川盆地尤为严重,已成为继京津冀、长江三角洲和珠江三角洲之后的我国第四大重污染区。然而,关于中国西南地区空气污染的气象成因、特别是干旱对当地空气污染影响的研究鲜有报道,而且高原南支槽活动对四川盆地空气污染的影响及其机理尚未引起关注,特别是四川盆地深盆地形对当地空气污染的影响仍不清楚。基于此,本文采用诊断分析和数值模拟方法,分析了中国西南地区的空气污染特征;对比研究了中国西南地区重污染区四川盆地与国内其它典型污染区的空气污染特征及其对气象条件的响应;对受高原南支槽活动影响的四川盆地典型重污染事件做了诊断分析和数值模拟研究;量化了四川盆地深盆地形对当地空气污染的影响;剖析了中国西南地区冬季空气污染与干旱大气环流背景及海-气遥相关型之间的关联性及其对当地干旱和非干旱事件的响应。主要研究结果如下:(1)中国西南地区空气污染事件主要发生在春冬季,其中,春季各个环境监测站的首要污染物主要为PM2.5、PM10和O3,冬季各个环境监测站的首要污染物主要为PM2.5和PM10;夏秋季空气污染轻,其中,夏季各个环境监测站的首要污染物主要为O3,秋季各个环境监测站的首要污染物主要为PM2.5。空间上,四川盆地是中国西南地区空气污染最严重的地区,云南省和贵州省次之,盆地外川西高原污染最轻;其中,四川盆地、贵州省和盆地外川西高原非达标率主要出现在冬季,而云南省的非达标率主要出现在春季。(2)通过对受高原南支槽活动影响的四川盆地典型重污染事件进行诊断分析和数值模拟研究,发现四川盆地重污染期间相对湿度约为70%,能见度较差(约8 km),气温约7.2 °C,风速较小(1~2 m/s),大气边界层高度较低,大气逆温非常显著,大气中水汽含量较高,对流层下沉运动占主导地位,700 hPa以下盛行偏南风。高原南支槽活动影响四川盆地空气污染的机理为:当四川盆地位于南支槽前时,一定强度和规模的西南气流受青藏高原和云贵高原大地形的影响在四川盆地上空形成背风坡垂直次级环流,同时西南暖湿气流的输送在四川盆地上空形成逆温层,产生“锅盖效应”,逆温层限定了低空次级环流的活动高度,进而制约了当地污染物在垂直方向的输送扩散范围,导致污染物在近地面积累,浓度迅速上升,产生空气重污染事件。当南支槽东移出四川盆地时,四川盆地上空逆温层逐渐减弱消失,背风坡垂直次级环流活动高度明显抬升,有利于大气污染物在垂直方向的稀释扩散,近地面污染物浓度降低,污染过程结束。(3)对比真实四川盆地地形高度(约500 m)和将盆底地形高度分别抬升至海拔2500 m和4000 m时WRF-Chem模式的数值模拟结果,发现四川盆地深盆地形是诱发当地出现高温、高湿、高海平面气压、低边界层高度、低风速和逆温层等不利大气扩散条件的主要原因;当盆底地形高度分别抬升至海拔2500 m和4000 m时,模拟的PM2.5浓度比真实四川盆地地形高度下模拟的PM2.5浓度分别降低82 μg m-3和112 μg m-3,计算的真实四川盆地地形对当地空气污染的贡献分别为54%和76%。因此,四川盆地空气污染气象成因与盆地深度密切相关。在污染源排放量不变的情况下,模拟结果显示深盆地形和由此所造成的不利于污染物扩散的气象条件共同作用是诱发四川盆地易出现重空气污染的两个重要因素,也是导致四川盆地成为中国西南地区空气污染最严重的关键地理和气象原因。(4)EOF主成分分析表明,1980–2012年中国西南地区冬季霾日(代表污染日)数有两个主要模态。第一模态解释方差为25.9%,空间上霾日数呈西北-东南偶极子变化,最强信号分别出现在川西高原和广西省西部;第二模态解释方差为10.2%,空间上霾日数呈现同位相变化,最强信号出现在四川盆地。运用回归分析和合成分析方法,探究中国西南地区冬季空气污染与当地干旱大气环流特征及海-气遥相关型之间的关联性,结果发现,欧亚大气遥相关型、负位相的极地/欧亚大气遥相关型、负位相的北极涛动、以及海洋上负位相的北大西洋涛动和拉尼娜事件均可诱发我国西南地区冬季空气污染潜势加重,为当地月尺度的空气污染潜势预报的开展提供了重要的科学依据,弥补了当前仅有空气质量中短期预报的不足。(5)资料分析和数值模拟均表明,干旱条件下我国西南地区气象条件发生了显著的变化,降水量和降水日数的减少导致湿清除效应减弱;边界层高度和相对湿度降低,形成了不利于污染物扩散的气象条件,导致污染物浓度上升,诱发空气污染事件。WRF-Chem模式不仅很好地模拟了干旱和非干旱条件下我国西南地区气象要素(降水量、2 m气温、海平面气压、相对湿度、地面风场和边界层高度)和污染物(PM2.5、PM10、CO、NO2、SO2和O3)浓度的时空变化,而且很好地再现了我国西南地区冬季空气污染对当地干旱和非干旱事件的响应,进一步从动力学和热力学的角度客观反映了当地干旱影响空气污染的物理过程及作用机制,为深化此类研究提供了本地化模式支持。总之,本文的研究结果进一步揭示了我国西南地区、特别是四川盆地空气污染的气象学成因及其机理,尤其是我国西南地区冬季空气污染与当地干旱大气环流特征及海-气遥相关型的关联特征,为当地月尺度的空气污染潜势预报的开展提供了重要科学依据,有助于当地短期空气质量预报水平的进一步提高,丰富和发展了复杂地形区域空气污染气象学的理论内涵。
Other AbstractAir pollution events are usually caused by adverse meteorological conditions and excessive emission of air pollutants. Southwest China (SWC) is affected by complex terrain and plateau weather system. As a result, the atmospheric diffusion conditions in winter over SWC are different from other areas, result in air pollution events occur frequently over SWC, especially in the Sichuan Basin of SWC, which has become the fourth of heavily polluted regions in China following the Beijing-Tianjin-Hebei region, the Yangtze River Delta and the Pearl River Delta. However, little attention has been paid to the meteorological causes of air pollution over SWC, especially the impact of winter drought on local air pollution. Moreover, the impact of the activities of the south branch trough of the Tibetan Plateau on air pollution in the Sichuan Basin and its mechanism are still unclear. Additionally, the effect of bowl-shaped basin on local air pollution is badly in need of research. Therefore, this study was carried out from the following aspects with the methods of diagnostic analysis and numerical simulation. (1) Air pollution characteristics over SWC was analyzed. (2) Air pollution characteristics and their responses to meteorological conditions among the four mostly polluted areas in China were compared. (3) A typical heavy air pollution event induced by the activities of the south branch trough of the Tibetan Plateau in the Sichuan Basin was investigated. (4) Impact of bowl-shaped deep basin on local air pollution was quantified. (5) The association between winter air pollution and atmospheric circulation background of winter droughts over SWC was explored. (6) The response of winter air pollution over SWC to local drought and non-drought events was quantified. Some main conclusions are as follows: (1) Air pollution over SWC is serious in spring and winter, with PM2.5, PM10 and O3 as the primary pollutants in spring, and PM2.5 and PM10 as the primary pollutants in winter. Air pollution in summer and autumn is light, with O3 as the primary pollutant in summer, and PM2.5 as the primary pollutant in autumn. Spatially, air pollution in the Sichuan Basin is the most serious over SWC, followed by Yunnan and Guizhou provinces, and western plateau is the least polluted. The number of non-attainment days in the Sichuan basin, Guizhou Province and western plateau mainly appeared in winter, while that in Yunnan Province mainly occurred in spring. (2) It has been found that the relative humidity was about 70%, the visibility was poor (8 km), the temperature was low (7.2 °C), and the wind speed was small (1~2 m/s) during the period of heavy air pollution in the Sichuan Basin. Moreover, the boundary layer height was low, the atmospheric inversion layer was very significant, the water content in the atmosphere was high, the subsidence dominated in the troposphere, the southerly wind prevailed below 700 hPa. The mechanisms of the activities of the south branch trough of the Tibetan Plateau affecting air pollution of the Sichuan Basin are as follows. When the Sichuan basin is in the front of the southern trough, southwest airflow affected by the Tibetan Plateau and Yunnan-Guizhou Plateau formed a leeward slope vertical secondary circulation above the Sichuan Basin. Meanwhile, warm and humid air flows transported by southwesterly formed inversion layer over the Sichuan Basin, producing “pot lid effect”. Thus, the inversion layer defines the activity height of the low-level secondary circulation, and further restricts the vertical transportation and diffusion range of air pollutants, leading to air pollutant concentrations near the ground increasing rapidly. When the south branch trough moved east out of the Sichuan Basin, the inversion layer over the Sichuan Basin weakened and disappeared, and the activity height of the leeward slope vertical secondary circulation increased significantly, which was conducive to the dilution and diffusion of air pollutants in the vertical direction. The concentrations of air pollutants near the ground decreased. (3) Compared to the PM2.5 levels under simulations of elevated Sichuan Basin topography with altitudes of 2500 m and 4000 m, the PM2.5 levels simulated under the real Sichuan Basin topography were comprehensively enhanced with an average increase reaching up to 82 μg m-3 and 112 μg m-3, indicating that the basin contributed 54% and 76% PM2.5 to the heavy air pollution event, respectively. The bowl-shaped topography was the main cause of high temperature, high humidity, high sea level pressure, low atmospheric boundary layer height, low wind speed and inversion layer over Sichuan Basin. When the amount of the natural and anthropogenic emissions is a constant, the bowl-shaped topography together with adverse meteorological conditions are the main factors inducing heavy air pollution over Sichuan Basin. (4) The number of winter haze days over SWC has two main modes. The first leading mode, accounting for 25.9% of the variance, displayed a northwest-southeast dipole pattern over SWC, with the two anomalous centers locating over the Western Sichuan Plateau and Western Guangxi Province, respectively. The second leading mode, accounting for 10.2% of the variance, primarily reflected the spatially in-phase change pattern, the number of winter haze days over SWC changing synchronously with the strongest signal over the Sichuan Basin. Regression analysis and synthetic analysis were used to explore the association between winter air pollution and atmospheric circulation background of winter drought over SWC. It has been found that atmospheric teleconnections associated with winter air pollution over SWC were La Niña events, conventional Eurasian teleconnection, and negative phases of Polar/Eurasia pattern, Arctic Oscillation and North Atlantic Oscillation. This provides an important scientific basis for the local monthly air pollution prediction, and makes up for the shortage of short- and medium-term air quality prediction. (5) Data analyses and numerical simulations showed that the meteorological conditions over SWC have changed significantly under drought conditions. Precipitation, the number of precipitation days, atmospheric boundary layer height and relative humidity all decreased during the droughts, resulting in unfavorable conditions for the dispersion of air pollutants. WRF-Chem model not only simulated the spatial and temporal characteristics of the meteorological parameters (rainfall, 2 m temperature, sea level pressure, relative humidity, atmospheric boundary layer height) and air pollutant (PM2.5, PM10, CO, NO2, SO2 and O3) concentrations, but also reproduced the responses of winter air pollution over SWC to local drought and non-drought events, reflecting the physical processes and mechanisms of winter droughts affecting air pollution from the perspectives of kinetics and thermodynamics. The results of this study further reveal the meteorological causes and mechanisms of air pollution in the Sichuan Basin. Particularly, the association between winter air pollution and atmospheric circulation background of winter drought over SWC not only provides important scientific basis for the development of monthly-term air pollution potential forecast, but also is helpful to improve the forecast accuracy of local short-term air quality, enriching and developing the theoretical connotation of meteorological causes of air pollution over the region with complex terrain.
Pages161
URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/338286
Collection大气科学学院
Affiliation大气科学学院
Recommended Citation
GB/T 7714
胡钰玲. 中国西南地区冬季空气污染气象成因的诊断分析和数值模拟研究[D]. 兰州. 兰州大学,2019.
Files in This Item:
There are no files associated with this item.
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Altmetrics Score
Google Scholar
Similar articles in Google Scholar
[胡钰玲]'s Articles
Baidu academic
Similar articles in Baidu academic
[胡钰玲]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[胡钰玲]'s Articles
Terms of Use
No data!
Social Bookmark/Share
No comment.
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.