青藏高原典型高寒森林地带CH4浓度特征分析

基于波长扫描光腔衰荡光谱线监测系统在海螺沟国家大气背景站(以下简称海螺沟站)开展甲烷(CH_4)连续自动监测,通过局部近似回归法进行背景值筛分分析。结果表明:2016、2017年海螺沟站CH_4年均体积分数和筛分的背景体积分数接近,两者浓度水平与北半球中纬度地区全球本底站CH_4浓度水平相当;海螺沟站CH_4能够代表背景区域浓度水平。海螺沟站CH_4体积分数呈春、夏季低,秋、冬季高特征,季节变化主要受到特定的地理环境和大气环流的影响,大气环流占主导影响。夏季CH_4体积分数最低但日振幅最大,与高原高海拔背景下森林地带的辐射对流引起局地扩散作用有关。采用逐步逼近回归筛分CH_4监测数据,海螺沟站CH_4背景季浓度变化和北半球中高纬度地区其他背景站大气CH_4的季节变化特征以及CH_4季体积分数振幅基本一致。背景站四季的CH_4载荷贡献在16个风向分布结果表明,在春、夏季存在西风带下南亚方向污染物气团的远距离输送;青藏高原东部近地面在冬季处于反气旋冷高压控制下,而SSW方向风向能够短暂打破这种稳定的气象条件,污染物得到迅速扩散,SSW为负贡献。

Analysis of CH4 Background Concentration Characteristics of the Alpine Forest Zone in Qinghai-Tibet Plateau

The atmospheric CH₄ were continuously monitored in the national atmospheric background station of Hailuogou based on optical cavity ring-down spectroscopy method, and the background value was screened through the local approximation regression method.The results showed that the annual average volume fraction of CH₄ was close to screening background volume fraction of Hailuogou in 2016 and 2017, and their concentrations were comparable to those of the global background stations in the mid-latitudes of the northern hemisphere.The CH₄ concentration in Hailuogou station was characterized by low concentration in spring, summer and high concentration in autumn and winter.Seasonal changes were mainly influenced by specific geographical environment and atmospheric circulation, which is the dominant influence.In summer, the CH₄ volume fraction was the lowest but the daily amplitude was the largest, which was related to the local diffusion caused by radiation convection in forest area under the background of high altitude of plateau.The observation data of CH₄ by step approximation regression screening showed that the seasonal variation of CH₄ background concentration in Hailuogou station was basically consistent with the seasonal variation characteristics of atmospheric CH₄ and the seasonal concentration amplitude of CH₄ in other background stations in the middle and high latitudes of the northern hemisphere.The distribution of the background station CH₄ load contribution in 16 wind directions in four seasons showed that in spring and summer, there was long distance transport of pollutant air masses in South Asia under westerly belt.Under the control of near-surface anticyclone cold high pressure in the east of Qinghai-Tibet Plateau in winter, the SSW direction of the wind could temporarily break the stable meteorological conditions, the pollutants got rapid diffusion, SSW was a negative contribution belt.