青藏高原UTLS气溶胶层形成机制及火山爆发影响的数值模拟研究

Recent observations by satellites have shown an aerosol layer existing in the upper troposphere and lower stratosphere (UTLS) over the larger Tibetan Plateau (TP) area during Asian summer monsoon. Such aerosol layer is also named as “Asian Tropopause Aerosol Layer”(ASAL),and its source and formation mechanism is not yet fully understood. With this proposal, we plan to use an atmospheric chemistry - general circulation model with coupled stratosphere and troposphere processes, together with various satellite and ground-based remote sensing observational data, to investigate physical-chemical processes during the transport of aerosols and their gaseous precursors from the boundary layer to the ASM anticyclone, and evaluate the effect of pollution from South and Southeast Asia on the UTLS aerosol layer over TP. We will investigate the physical-chemical processes during the transport of SO2 ejected from the June 2011 Nabro volcano to the ASM anticyclone, and evaluate the effect of the volcano eruption on the UTLS aerosol layer over TP. We will also investigate the chemical transport and transform processes of aerosols and their gaseous precursors within the TP anti-cyclone, and evaluate the impact of both the boundary pollution sources and volcano eruption on the physic-chemical characteristics of aerosols in the UTLS. The proposed study will be helpful for revealing the source, physic-chemical characteristics and formation mechanism of aerosols in the UTLS and further understanding the mechanism of troposphere-stratosphere interactions over TP.

近年来的卫星观测研究发现，亚洲夏季风期间在青藏高原及邻近地区上空上对流层和下平流层（UTLS）区域存在一气溶胶层，亦称之为“亚洲对流层顶气溶胶层”，其来源和形成机制还不十分清楚。本项目拟采用平流层和对流层耦合的大气化学-环流模式，结合各种卫星和地基遥感观测资料，研究气溶胶及其前体物自亚洲地区边界层向ASM反气旋输送中的物理化学过程，评估南亚、东南亚污染对高原UTLS气溶胶层形成的影响；研究Nabro火山爆发释放的SO2向ASM反气旋输送中的物理化学过程，评估火山爆发对高原UTLS气溶胶层形成的影响；研究气溶胶及其气态前体物在高原反气旋内的化学输送和转化机制，综合评估人为污染和火山爆发对高原UTLS气溶胶层形成的相对重要性。项目研究有助于深入揭示青藏高原UTLS气溶胶的来源、理化特征和形成机制，加深对青藏高原对流层－平流层相互作用机理的认识。

本项目用高分辨率 (T106L90) 的全球大气化学环流模式EMAC，模拟研究了2010-2012年期间亚洲夏季风反气旋上对流层和下平流层（UTLS）气溶胶的化学组成和来源。结果发现在青藏高原UTLS 气溶胶消光出现最大值，这些气溶胶主要来自青藏高原北部及其北坡区域，在这些区域排放的气溶胶被直接抬升到10公里高度，然后在反气旋内输送。模拟研究表明，ASM反气旋UTLS气溶胶消光主要来自沙尘气溶胶的贡献，其次亲水性气溶胶和液态水气溶胶。由于反气旋内高浓度背景气溶胶的遮掩，反气旋内对流层顶附近大范围高浓度值的气溶胶层并不十分明显，在有Nabao火山喷发的2011年甚至出现了反-ATAL情景，即：反气旋内气溶胶消光出现大范围的最小值。模拟结果显示，沙尘、硫酸盐和硝酸盐是ASM反气旋UTLS中干气溶胶的主要成分，沙尘和硝酸盐浓度会随着高度增加而降低，而由于火山爆发对低平流层的影响大于对上对流层的影响，硫酸盐气溶胶的浓度会随着高度增加而升高。本项目研究表明，青藏高原中对流层不仅对周边污染物而且还对自然气溶胶和气体起到输送导管的作用，这些天然和污染气体和气溶胶在反气旋中的相互作用十分复杂，需要进一步深入研究。