2021年春季沙尘传输对徐州地区气溶胶演变影响分析

Analysis of impact of dust transport on aerosol evolution in Xuzhou region in spring 2021

沙尘气溶胶对局地大气环境具有显著影响。基于2021年3月中国东部卫星和地基遥感观测资料,以沙尘传输过程中上下游的两个城市北京和徐州为主要研究区,分析了两地气溶胶环境的阶段性变化特征和驱动因子。结果表明:(1)连续两次大型沙尘暴均来源于蒙古地区,并受冷空气驱动影响中国东部地区,第一次沙尘在江苏腹地进入黄海,第二次沙尘在江苏省附近受西南暖风影响发生沙尘回流现象造成持续污染。(2)沙尘以粗颗粒物为主,使得近地面层PM_(10)浓度急剧提升至背景值的20倍、PM_(2.5)提高至3倍。处于下游的徐州地区比上游的北京地区两次PM_(10)峰值均低500μg·m^(−3),且时间延后12 h。(3)沙尘过境前徐州背景气溶胶以散射性细颗粒物为主,气溶胶光学厚度(AOD)小于0.5,单次散射反照率(SSA)约等于0.99。到达徐州地区的沙尘漂浮在2∼4 km高空层并随重力作用与地面层气溶胶混合,使得AOD瞬间提升至1.5以上,24 h后开始逐步由沙尘主导过渡到本地污染物粒子主导(气溶胶退偏比从大于0.25降至0.1以下)。本次沙尘中部分颗粒物成分对440 nm光谱吸收性较强,与沙尘来源有关。

Dust aerosols have a significant impact on the local atmospheric environment.Based on the satellite/groundbased remote sensing observation data of eastern China in March 2021,the periodic characteristics and driving factors of aerosol environment in Beijing and Xuzhou,China,the upstream and downstream cities along the transport pathway of dust,are studied in this work.The results show that:(1)The two consecutive large-scale dust storms were driven by cold air from Mongolia to eastern China.The first dust entered the Yellow Sea in the middle part of Jiangsu province,and the second dust recirculation occurred near Jiangsu Province under the influence of southwest warm wind,resulting in continuous pollution.(2)The sand dust was mainly coarse particles,which made the PM_(10) concentration in the near surface layer rise sharply to 20 times of the background value and PM_(2.5) to 3 times.Xuzhou in the downstream was 500μg·m^(−3) lower than Beijing in the upstream,and the time was delayed by 12 hours.(3)The background aerosol in Xuzhou was mainly scattered fine particles,the aerosol optical thickness(AOD)was less than 0.5,and the single scattering albedo(SSA)was about 0.99.When the sand storm arrived in Xuzhou,it floated in the upper layer of 2∼4 km and mixed with the aerosol underlying layer with the action of gravity,so that AOD instantly increased to more than 1.5.After 24 hours,it began to gradually transition from sand dust dominated to local pollutant particles dominated(the aerosol depolarization ratio decreased from more than 0.25 to less than 0.1).It is also found that some particles in the dust had strong absorption to 440 nm spectrum,which was related to the source of dust.