气候变化下我国华北地区热浪和静稳天气对臭氧影响的高精度区域模拟研究

The ozone concentrations over North China (including Jing-Jin-Ji region, Shandong and the surrounding areas) have been increasing over the past few years. The high ozone concentrations are not only closely related to anthropogenic emissions, but also strongly influenced by meteorology such as heat waves and atmospheric stagnation. Focusing on the ozone pollution problem in North China, this study applies dynamical downscaling technique to conduct high spatial resolution (12 km) regional climate and air quality simulations using WRF-CMAQ. By combining both modeling and observational data, this study will construct the temporal and spatial correlations between extreme weather events and high ozone pollution episodes and examine in detail the underlying mechanism for severe ozone pollution. By applying dynamical downscaling method based on multiple global climate models (GCMs), this study explores the impact of climate change on extreme weather events such as heat waves and atmospheric stagnation, as well as the impact of these extreme weather events on ozone pollution in North China. Meanwhile, this study focuses on modeling and analyzing how extreme weather events modulate the ozone changes through modulation of atmospheric transport as well as local photochemical reactions, thus it may provide important guidance for the control of severe ozone problems in North China.

我国华北地区（包括京津冀、山东及周边）臭氧浓度近年来持续升高。高浓度臭氧污染一方面与人为污染源排放紧密相关，另一方面也受到气象因素如高温热浪和静稳型天气的影响。针对华北地区臭氧污染现状，本研究将采用动力降尺度方法，通过区域气候和空气质量模式WRF-CMAQ进行高精度（空间分辨率为12公里）模拟。综合利用模拟和观测数据剖析当前极端天气与臭氧污染的时空相关性，深入理解高浓度臭氧污染形成的天气和气候原因。通过选择多个全球模式驱动进行动力降尺度区域模拟，探讨本世纪中叶气候变化下华北地区高温热浪和静稳天气等极端气象对臭氧的影响。同时,本研究着力于模拟和分析极端天气如何通过影响大气传输及局地化学反应进而影响臭氧浓度,从而为我国华北地区臭氧的防控提供重要的科学根据。

我国华北地区近年来臭氧污染严重。本研究首先聚焦2017年6月华北臭氧重污染事件，通过WRF-CMAQ模拟，指出了高温热浪、静稳天气促进高浓度臭氧累积的气象因素，揭示了常用的土地覆盖类型水平分辨率较低无法识别城市绿地，过去研究忽视了城市绿地天然源排放对臭氧的重要作用。考虑到天然源排放随树种不同差异较大，我们提出一方面城市绿化过程中需慎重考虑树种选择，另一方面构建我国城市绿地排放天然源清单对理清其在臭氧污染的贡献至关重要。其次，基于对臭氧生成物理化学过程的追踪，发现：1）在高浓度（如MDA8臭氧大于70 ppbv）臭氧时段，边界层内光化学反应几乎是臭氧浓度增加的唯一来源，且与地面高浓度MDA8臭氧显著正相关；2）相对于单日减排，连续减排可通过降低初始场大大减少臭氧浓度累积；3）除本地污染源外，外部地区传输影响显著。基于此，提出动态减排策略，如臭氧高污染累积时段和污染前1-2天的减排，以及周边区域减排。最后，基于CMIP5 RCP情景，发现人为源减排可导致华北未来臭氧浓度降低；仅考虑气候变化，臭氧超标天数将增加。因此指出我国华北地区未来臭氧污染治理应同时考虑气候变化和污染排放的作用，以及理清气候变化、污染源对臭氧协同调控机制的重要性。