兰州大学机构库
气溶胶对城市边界层的影响机制研究
Alternative TitleAN INVESTIGATION OF THE INFLUENCE MECHANISM OF ATMOSPHERIC AEROSOLS ON URBAN BOUNDARY LAYER
马永敬
Subtype博士
Thesis Advisor张文煜 ; 辛金元
2020-09-28
Degree Grantor兰州大学
Place of Conferral兰州
Degree Discipline大气物理学与大气环境
Keyword北京城市站 大气气溶胶 城市边界层 影响机制 大涡模型DALES
Abstract随着中国经济和城市化的迅猛发展,我国大部分地区出现不同程度的颗粒物污染。高浓度的大气污染物不仅给人类的社会生产生活带来了巨大影响,同时也严重威胁了人类的身体健康。研究发现,除了一次气溶胶及气态前体物的大量排放和二次气溶胶的快速生成外,气溶胶与边界层的相互作用也是导致污染累积爆发的一个重要诱因。气溶胶作为污染物,可以通过辐射效应影响地表能量平衡,进而直接或间接影响边界层结构,而边界层控制大气垂直扩散能力,其高度变化又直接影响污染的变化,即气溶胶-边界层的反馈系统。论文利用中国科学院大气物理研究所北京城市站多年观测数据,结合微尺度湍流大涡模型DALES(Dutch Atmospheric Large Eddy Simulation, version-4.1),分别从观测和模拟两个角度研究了气溶胶对城市边界层的影响机制,并进一步探讨了气溶胶浓度、散射吸收能力以及气溶胶层垂直高度对边界层发展的影响。 北京地区2010-2017年的观测数据分析表明,气溶胶光学厚度(Aerosol optical depth, AOD)及辐射强迫绝对值呈明显下降趋势,表明我国大气污染治理措施卓有成效,晴空边界层高度(Planetary boundary layer height, PBLH)呈上升趋势。污染条件下,大气静稳,水汽在边界层内累积,相对湿度高,PBLH随AOD的增加而降低,表明高浓度气溶胶是污染条件下抑制边界层发展的重要因素。 为精确解析边界层内各气象、物理参数变化特征,采用耦合陆面-辐射模块的大涡模型DALES针对北京地区典型静稳天气污染个例进行模拟,研究发现DALES可以很好的重现静稳天气污染个例的边界层内各气象、物理参数的日变化特征,证明DALES在模拟城市污染边界层的热动力结构方面具有很好的适用性。气溶胶浓度敏感性实验模拟中,增加吸收性气溶胶浓度可以增强上层大气加热效应和底层大气冷却效应,形成强稳定层结,显著抑制边界层发展。在气溶胶散射吸收特性敏感性实验模拟中,增强气溶胶的散射能力会造成上层大气冷却和底层大气的加热,使得大气层结稳定性减弱,边界层发展更充分,即吸收性气溶胶较散射性气溶胶更能抑制边界层的发展。同时与以往研究对比发现大气中同时存在吸收性气溶胶更抑制和散射性气溶胶更抑制两种情景。 以该典型静稳天气条件热力结构为背景,设计了一系列敏感性实验,系统性研究气溶胶散射吸收能力对边界层发展的影响。研究发现不同类型气溶胶对边界层的作用与气溶胶层的垂直位置有关。位于残留层之下的局地排放的吸收性气溶胶表现为火炉效应,加热残留层和稳定边界层,促进边界层的发展;位于残留层之上的传输型吸收性气溶胶表现为穹顶效应,强烈加热逆温层,抑制边界层发展;散射性气溶胶对边界层热力结构没有热量输入,仅通过阳伞散射效应削弱到达地面的辐射而抑制边界层发展,但抑制作用弱于穹顶效应,且与残留层上下位置无关。由此发现大气中存在一个转换高度h,在h之上,吸收性气溶胶较散射性气溶胶更抑制边界层发展(即,穹顶效应>天空阳伞效应);而在h之下,散射性气溶胶较吸收性气溶胶更抑制边界层发展(即,地面阳伞效应>火炉效应)。该转换高度h与残留层的高度密切相关。气溶胶穹顶和阳伞效应可被解读为双重抑制效应,成功地从光学辐射角度解释了华北平原雾霾形成机制,并强调了在污染防控中实施具有针对性的精准治理的重要性,对于京津冀上空的传输型气溶胶,要加强管控华北平原南部上风向地区的燃煤、秸秆焚烧等吸收性污染物(黑碳、棕碳)高排放的燃烧活动;而对于华北平原局地地区,应加大力度实施机动车限行、燃煤的脱硫处理等措施,减少散射性气溶胶及前体物的排放。根据双重抑制效应所提出的精准管控,协同治理方案,对污染的防控具有重要指导意义。 针对传输型气溶胶(残留层上层自由大气气溶胶),发现吸收性气溶胶对边界层的作用存在一个穹顶效应绝对有效高度z。在z之下,吸收性气溶胶表现为穹顶效应,强烈抑制边界层发展,随着气溶胶层的提升,对边界层抑制作用减弱;当气溶胶层高于z之后,气溶胶层对边界层的抑制作用保持一个常值,定义为虚拟穹顶效应。对于纯散射性气溶胶来说,无论其在残留层之上的垂直位置如何,对边界层均表现为相同的抑制作用,但相对于虚拟穹顶效应来说抑制作用更弱,同样定义为天空阳伞效应。气溶胶火炉、穹顶、虚拟穹顶、地面和天空阳伞效应形象阐明了不同类型气溶胶位于不同高度时在城市边界层发展过程中所扮演的角色,深化了我们对气溶胶-边界层相互作用机理的认识。
Other AbstractWith the rapid development of 中文na's economy and urbanization, severe particulate matter pollutions, also known as haze, have appeared in most regions of 中文na. These high-concentration pollutants not only affect the social life, but also threaten the human’s health. Therefore, scientists both at home and abroad have made great efforts to explore the cause of these haze events. They found that apart from the high emissions of primary aerosols and gas precursor and the fast formation of secondary aerosols, the interactions between aerosols and planetary boundary layer (PBL) are also important in triggering the haze episode. Aerosols affect the surface energy balance through radiation effect, therefore directly or indirectly change the thermal structure of boundary layer. On the other hand, the boundary layer determines the atmospheric vertical diffusion ability and the change of planetary boundary layer height (PBLH) controls the variation of pollutant concentrations, forming the aerosol-PBL feedback system. Herein, at the basis of the multi-year observations of BeiJing City site of the Institute of Atmospheric Physics, coupling with a large-eddy simulation model, we elucidate the influence mechanism of atmospheric aerosols on PBLH through both observations and modeling. Furthermore, how aerosol loading, scattering ability and the vertical aerosol distribution affect the development of PBL is systemically investigated. Statistics of the long-term observations of 2010-2017 shows a decline of aerosol optical depth (AOD) and the absolute value of aerosol radiative forcing, indicating the effective control of the 中文nese government policy. The planetary boundary layer height (PBLH) shows an upward trend. For polluted conditions, the atmospheric stratification is stable and the water vapor is accumulated within the boundary layer. The PBLH decreases with the increase of AOD, suggesting the high concentration of aerosols seriously suppresses the boundary layer. To accurately resolve the properties of the boundary layer meteorological and physical variables, we used a large-eddy simulation model named as DALES coupling with radiation and land surface modules to simulate a stagnant weather case over Beijing. Results show that DALES performed satisfiedly in reproducing the diurnal variation of the variables, demonstrating the ability of DALES in simulating the boundary layer thermodynamic structures. We observe an enhanced upper-atmosphere heating and a lower-layer cooling in the scenario of increasing absorption aerosol loadings. In the sensitivity experiment of aerosol scattering ability, the enhancement of aerosol scattering property leads to a vigorous convection through weakening the upper-atmosphere heating and lower-layer cooling, demonstrating that the absorption aerosols suppress PBL more than the scattering aerosols. In order to systematically investigate the influence of aerosol scattering ability on PBL development, a series of sensitivity experiments were designed based on the thermodynamic structure of this typical stagnant weather condition. The impact of scattering and absorption aerosols on PBL are found to be closely related to the vertical position of aerosol layer. The local emission of absorption aerosols below the residual layer acts as a stove effect, heats the underneath stable boundary layer and residual layer, promotes the development of PBL. The absorption aerosols above the residual layer heat the upper inversion layer, str英语then the atmospheric stability, and strongly inhibit the PBL, which is defined as dome effect. The impact of scattering aerosols depends on the loadings rather than the vertical position because they have no heat input to the thermal structure of the boundary layer. Only the umbrella effect backscattering the solar radiation weakens the radiation rea中文ng to the ground surface and inhibits the PBL. However, this inhibition effect is weaker than the dome effect. It is, therefore, found that there exists a transition height h in the atmosphere, above which, the absorption aerosols inhibit PBL more than the scattering aerosols (i.e., dome effect > aloft umbrella effect), while below which, the scattering aerosols dominate the suppression of PBL rather than absorption aerosols (i.e., stove effect < surface umbrella effect). This height is highly related to the height of the residual layer. The aerosol dome and umbrella effects can be interpreted as a double-inhibition effect on the formation mechanism of North 中文na Plain haze event. For the aerosol suspending on the North 中文na Plain region, i.e. transport aerosols, we emphasize the importance of controlling the coal and straw burning which producing high amount of absorption pollutants (i.e., Black carbon, BC; Brown carbon, BrC) over the southern area. For the local region of North 中文na Plain, measures such as vehicle restrictions and desulfurization of coal burning should be str英语thened to reduce the emission of scattering aerosols and precursors. The precise and coordinated control schemes proposed based on the double-inhibition effect have important guiding significance for the prevention of air pollutions. For the transport aerosols (i.e., aerosols above the residual layer or free atmosphere aerosols), it is found that there is a dome effective height z for the effect of absorption aerosols on the PBL. Below z, absorption aerosols exihibit as the dome effect, suppress the PBL. This dome inhibition weakens as the evaluation of aerosol layer. When the aerosol layer is higher than z, the inhibition of aerosol layer on the boundary layer maintains a constant value, which is defined as the virtual dome effect. The scattering aerosols show the same inhibition performance regardless of their vertical position (from residual layer to ∞), but to a weaker extent than the virtual dome effect, denoted as aloft umbrella effect. Aerosol stove, dome, virtual dome, and surface/aloft umbrella effects visualize the impacts of different types of aerosols located at different heights on the evolution of PBL, which deepens our understandings on the aerosol-PBL interactions.
Pages114
URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/448512
Collection兰州大学
Affiliation大气科学学院
Recommended Citation
GB/T 7714
马永敬. 气溶胶对城市边界层的影响机制研究[D]. 兰州. 兰州大学,2020.
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