长三角典型城市空气污染与大气边界层相互作用机制的观测与模拟研究

Characterized with high concentration of fine particular matter (PM), the regional-scale complex atmospheric pollution has brought serious challenge to the ecosystem and society. Recent studies showed that the concentration of PM was high enough to modify meteorological conditions in the Planetary Boundary Layer (PBL), which are key factors influencing the air quality, and hence to enhance the air pollution through this feedback loop. However, because of a lack of comprehensive integrated observations, especially those for the vertical measurement of the physical and chemical parameters in the PBL, there are high uncertainties in the understanding of quantitative impact of such kind of feedback on the regional haze pollution.. Here, we propose a study to address this issue in the Yangtze River Delta, a region with heavy haze pollution and relatively strong solar radiation. Intensive field complains will be conducted at several super-sites in Nanjing, a city downwind of the YRD city cluster, to detect the vertical structure of PBL physical and chemical parameters and multi-processes/ parameters around the ground surface. Based on these data, we will investigate the contributions of surface energy budget and vertical heating induced by aerosol layers to the development of PBL, and will also try to quantitatively understand the influence of local air pollution accumulation, enhanced by the change of PBL dynamics, and that of secondary formation induced by the change in meteorology conditions. We will improve the meteorology-chemistry two-way coupled numerical model by using optimized parameterization schemes or key parameters based on the measurement and our new findings. This model will be use to quantitatively understand the impact of air pollution-PBL feedback on regional haze pollution from a larger scale. Relevant control policy will also be raised to improve the air quality efficiently by considering the air pollution-PBL feedback.

以细颗粒为特征的大气复合污染问题对我国东部地区生态环境带来严峻挑战。近期的研究表明，当前我国重污染地区颗粒物浓度之高，足以影响与空气污染形成自身所密切相关的大气边界层气象条件，从而通过反馈作用加剧污染。然而，由于缺乏比较系统的集成观测（尤其是垂直理化结构的观测），目前对相关过程在大气复合污染形成中的定量贡献在认识上尚有较高的不确定性。本项目拟在颗粒物浓度高、太阳辐射强的长三角地区开展研究。通过在城市群下风向的南京开展多超级站的协同观测，探测大气边界层垂直方向理化结构和地基多过程、多参数，揭示地表能量平衡和大气辐射加热在边界层演变中的贡献，认识大气层结变化所引起的局地污染积累与二次污染转化速度的改变对复合污染形成的影响；同时针对双向反馈模型关键过程参数化方案和关键参数选择进行优化，从而定量研究空气污染-大气边界层相互作用对区域大气复合污染形成的贡献，并针对相关问题提出控制对策建议。

本项目旨在基于外场试验和数值模拟的方法开展长三角典型城市空气污染与大气边界层相互作用机制的观测与模拟研究。项目首先基于历史资料对空气污染-大气边界层相互作用规律的诊断分析研究，利用北京、南京等地的黑碳和细颗粒物外场观测、飞机航测数据、气象站气球探空数据和南京大学地球系统区域过程综合观测试验基地SORPES站的边界层理化结构、辐射和地表感热潜热通量观测数据，结合区域大气动力-化学耦合模式WRF-Chem和一维的辐射传输和边界层耦合模式深入分析了冬季灰霾期间具有强吸光性的黑碳气溶胶对短波辐射传输、地表长波辐射强度、感热潜热通量、大气温度层结、边界层发展以及近地面污染之间的交互反馈作用。研究发现黑碳可因其对可见光的强吸收作用冷却地表并加热1-2公里高度的大气，导致大气边界层的发展受到抑制，使得城市污染排放被限制在更低高度，从而显著加剧城市污染。此外，项目基于南京大学SORPES站在典型季节开展了强化观测试验对大气成分、边界层气象参数、地表能量平衡相关参数以及基于激光雷达、风温廓线雷达、GPS探空、系留气球探空等对关键气象参数和主要气溶胶浓度及其前体物在边界层内的垂直结构进行观测。并基于上述观测针对包括秋冬季节城市及工业复合污染、春季沙尘/扬尘以及夏初秸秆燃烧等不同类型的污染优化改进数值模拟并定量评估区域尺度上相关反馈过程对我国东部地区极端污染形成的定量贡献。