Abstract:

In order to study the development law and pollution characteristics of dust weathers, two strong sandstorm processes occurring in northern China in March 2021 (the processes on March 15 and 27, referred to as “3·15” process and “3·27” process, respectively) are analyzed based on polarized mie-scattering lidar observation data and hourly urban particulate mass concentration data in Shijiazhuang and Jinan. The results are as follows: (1) When the dust arrived, the mass concentration of PM₁₀ in the two cities increased rapidly, and the mass concentration ratio of PM_2.5 and PM₁₀ decreased rapidly. (2) The PM₁₀ mass concentration of the two cities conformed to the normal distribution during the two processes, and the determination coefficients of the Gaussian fitting of the PM₁₀ mass concentration in Shijiazhuang and Jinan during the “3·15” process and the “3·27” process were 0.92 and 0.76, 0.83 and 0.89, respectively. (3) During the dust outbreak period, the extinction coefficient and depolarization ratio near the ground increased significantly. (4) Due to dust sedimentation and different sources of dust, a multi-layer structure appeared during dust transport, which can be divided into near-surface dust layer, low-altitude dust layer and high-altitude dust layer. The appearance time of near-surface dust layer was basically consistent with the sharp rise time of ground particle mass concentration. (5) At the height of 195 m (close to the ground and with reliable radar data quality), the maximum depolarization ratio in Shijiazhuang and Jinan during the “3·15” process (the“3·27” process) was 0.29, 0.28 (0.23, 0.20), and the maximum extinction coefficient was 3.94, 3.84 km^-1 (3.10, 1.83 km^-1), respectively, which showed that the strength of dust became weaker and the large particles decreased continuously during the transport process. The time when the depolarization ratio at this height began to rise rapidly was about 1 h earlier than the time when the mass concentration of ground particles began to rise rapidly. (6) According to the pollution characteristics of dust weather, its development can be divided into four stages: the early stage, the outbreak stage, the maintenance stage and the late stage. The different stages of dust can be well identified by comprehensive use of PM₁₀ mass concentration, PM_2.5 and PM₁₀ mass concentration ratio, extinction coefficient and depolarization ratio.

Key words: dust, lidar, aerosol, Mongolia cyclone, particle mass concentration

摘要：

为探究沙尘天气发展规律和污染特征，以石家庄和济南为例，基于偏振-米散射激光雷达观测数据和城市颗粒物小时质量浓度等数据，分析2021年3月中国北方发生的两次强沙尘过程（3月15日与27日强沙尘过程，简称“3·15”过程与“3·27”过程）。结果表明：（1）两次过程沙尘入境时，两市PM₁₀质量浓度快速上升，PM_2.5与PM₁₀质量浓度比迅速减小。（2）两次过程期间，两市PM₁₀质量浓度符合正态分布，“3·15”过程石家庄和济南PM₁₀质量浓度高斯拟合的决定系数分别为0.92和0.76，“3·27”过程分别为0.83和0.89。（3）沙尘爆发期，近地面消光系数和退偏比都明显增大。（4）因沙尘沉降和多沙尘源，沙尘传输过程中出现多层结构，可分为近地面沙尘层、低空沙尘层和高空沙尘层。近地面沙尘层出现时间和地面颗粒物质量浓度急剧上升时间基本一致。（5）离地面近且雷达数据质量可靠的195 m高度处，“3·15”过程（“3·27”过程）石家庄和济南退偏比最大分别为0.29、0.23（0.28、0.20），消光系数最大分别为3.94、3.84 km^-1（3.10、1.83 km^-1）。表明沙尘在传输过程中强度变弱，大粒子不断减少。该高度退偏比开始快速上升时间比地面颗粒物质量浓度开始快速上升时间早约1 h。（6）根据沙尘天气污染特征可将其发展分为前期、爆发期、维持期和后期4个阶段，综合利用PM₁₀质量浓度、PM_2.5与PM₁₀质量浓度比、消光系数和退偏比等能很好地识别沙尘的不同阶段。

关键词: 沙尘, 激光雷达, 气溶胶, 蒙古气旋, 颗粒物质量浓度