天津典型沙尘天气过程颗粒物污染特征

Particulate Pollution Characteristics of Typical Sand Dust Weather in Tianjin

为了解天津市典型沙尘天气颗粒物污染特征,基于2018年天津市4次沙尘天气过程(沙尘日9 d)中高时间分辨率在线监测数据,结合后向轨迹模型开展沙尘天气下颗粒物污染特征分析。结果表明:沙尘天气下,总悬浮颗粒物(TSP)和可吸入颗粒物(PM 10)小时峰值质量浓度分别为2265和928μg·m-3,平均质量浓度达970和435μg·m-3;PM 10/TSP比值为0.45~0.83,PM 2.5/PM 10比值为0.17~0.29。沙尘天气下颗粒物个数浓度迅速下降,粒谱分布表现为个数浓度密度中心峰值浓度下降,并向粗粒子方向偏移,中心峰值所对应的粒径为0.67~1.72μm。阳离子Ca 2+、Na+、Mg 2+浓度显著增加,二次离子(NO 3-、SO 42-、NH 4+)浓度显著减少。沙尘天气5 km以下高空气溶胶的消光系数小且退偏振比大,退偏振比随时间明显增加且逐渐向地面传递。在2018年4次沙尘天气中沙尘气团从3 km左右的高空向京津冀地区输送,主要源地为蒙古国中部、南部和东南部,途径为北方路径或西北路径。

In order to understand the characteristics of particulate pollution in recent sand dust weather in Tianjin,characterization of particulate matter pollution during four typical sand dust weather processes(nine dust days)in 2018 were investigated based on high-resolution online monitoring data and backward track model.The results show that the hourly peak concentrations of TSP and PM 10 were 2265 and 928μg·m-3,and the average concentrations were 970 and 435μg·m-3,respectively.The mass ratios of PM 10 to TSP were 0.45-0.83,and the mass ratios of PM 2.5 to PM 10 were 0.17-0.29.The number concentrations of particulate matter decreased rapidly,and the distribution trend of particulate spectrum show that the peak of particulate number concentrations decreased,and shifted to the direction of coarse particles.The peak size spectrum of the dust was among 0.67-1.72μm.Chemical compositions concentrations of PM 2.5 showed different change characteristics during sand dust weather processes.Concentrations of cations such as Ca 2+,Na+and Mg 2+increased significantly,while the concentrations of secondary ions(NO 3-、SO 42-、NH 4+)decreased significantly.The extinction coefficients were smaller and the depolarization ratios were larger at altitude below 5 km of sand dust weather,and the depolarization ratios increased obviously with time and gradually transferred to the ground.As for four typical sand dust weather processes in 2018 in Tianjin,the sand dust mass was transported to Beijing-Tianjin-Hebei Region from an altitude of about 3 km with the northern path or the northwest path influence of Tianjin,and its main sources located at central,south and southeast part of Mongolia.