夏季青藏高原对流层臭氧年际变化及影响因子

Interannual Variation of Tropospheric Ozone over the Tibetan Plateau in Summer and Its Influencing Factors

基于2003—2022年ERA5(ECMWF reanalysis v5)再分析数据、AIRS(atmospheric infrared sounder)卫星数据和中国生态环保部的地面臭氧等数据,采用合成分析和相关分析方法发现夏季青藏高原地区对流层臭氧柱总量年际变化特征明显,并以每年约0.08 DU的速度增加。青藏高原地区对流层臭氧柱总量高低年份差异不仅与对流层高低层臭氧垂直分布直接相关,更与高低层动力和化学过程有关。分析发现:当青藏高原地区对流层臭氧柱总量偏高时,青藏高原北侧对流层顶偏低,副热带西风急流偏弱且存在断裂,较弱的传输屏障使平流层对流层交换增强,有利于平流层高浓度臭氧空气下传。对流层低层的垂直环流通过向上传输低浓度臭氧空气影响整个对流层臭氧浓度。此外,青藏高原西南部对流层整层的臭氧浓度偏低还与南亚高压异常有关,青藏高原腹地对流层臭氧柱总量偏高可能与地面污染物排放、地面太阳净辐射量异常偏高有关。

The Tibetan Plateau,located in the mid-latitude region of the Asian continent,is commonly referred to as the third pole and the water tower of Asia.The high-altitude terrain and distinct circulation systems contribute to the formation of an ozone valley in the atmosphere above the Plateau.The discovery of this ozone valley has garnered significant attention from the international scientific community regarding the ozone levels over the Tibetan Plateau.At the same time,in the context of global warming,the increase of surface ozone concentrations in various regions of the world has posed significant threats to both human health and ecological environment.However,due to limited observational data and satellite data of short time scales,past studies on the Tibetan Plateau’s ozone primarily focused on total column ozone,the upper troposphere and lower stratosphere,or surface ozone,while fewer studies have examined the tropospheric ozone column over the region.Therefore,longer-term data are needed to investigate the interannual variability and influencing factors of the tropospheric ozone column over the Tibetan Plateau.Based on AIRS(atmospheric infrared sounder)satellite data from 2003 to 2022,the tropospheric ozone column over the Tibetan Plateau during summer seasons from 2003 to 2022,as well as its interannual variation characteristics are analyzed.Additionally,using ERA5 reanalysis data from 2003 to 2022 and surface station data from China’s Ministry of Ecology and Environment from 2015 to 2022,the study employs composite and correlation analyses to explore the factors influencing the tropospheric ozone column over the region.Results show that the tropospheric ozone column over the Tibetan Plateau during the summer exhibits significant interannual variability,increasing at a rate of approximately 0.08 DU per year.The difference of total tropospheric ozone column in high and low years is not only directly related to the difference of vertical distribution of ozone in the upper and lower troposphere,but also related to the difference of dynamic and chemical processes in the upper and lower troposphere.When the total tropospheric ozone column over the Tibetan Plateau is elevated,the tropopause on the northern side of the Plateau is lower,and the subtropical westerly jet is weak and fragmented.The weak transmission barrier enhances stratospheric tropospheric exchange,which is beneficial to the downward transmission of stratospheric high-concentration ozone air,while the vertical circulation in the lower troposphere affects the ozone concentration in the whole troposphere by upward transmission of low-concentration ozone air in the lower troposphere.The tropospheric ozone column anomaly in the northern Plateau is primarily associated with tropopause folding,while the lower ozone concentration across the entire troposphere in the southwestern Plateau is linked to anomalies in the South Asian High.The elevated tropospheric ozone column over the central Plateau may be associated with unusually high levels of surface solar radiation and emissions from surface pollutants.