石家庄一次沙尘气溶胶污染过程及光学特性

为掌握沙尘气溶胶远距离输送特征及其规律,对2015年4月15日影响石家庄空气质量的沙尘天气背景、污染特征进行了分析,利用HYSPLIT—4模式分析了沙尘气溶胶的后向轨迹,并利用微脉冲激光雷达和太阳光度计CE318监测资料分析了沙尘气溶胶的垂直分布和光学特性演变,与大风无沙尘沉降另一过程进行了对比,探讨了沙尘沉降对消光系数的影响,估算了沙尘沉降对地面PM10浓度的贡献.结果表明:来自蒙古国的沙尘气溶胶以西北路径远距离输送沉降是导致石家庄PM10浓度骤升的主要因素;沙尘沉降对消光系数和地面PM10浓度具有重要贡献;气溶胶快速沉降时间与冷锋过境、冷空气下沉相一致;微脉冲激光雷达监测到整个沙尘气溶胶输送沉降过程,沉降之前沙尘气溶胶主要分布在1500~3000m高空,气溶胶消光系数随高度上升而增大,输送飘浮空中到沉降持续时间较长,为沙尘污染预警提供了"强信号"特征;气溶胶光学厚度随沙尘到达明显上升,浑浊度较高,粒径偏大,地面能见度随气溶胶光学厚度呈幂指数递减.

Pollution process and optical properties during a dust aerosol event in Shijiazhuang

In order to investigate the properties and variation of dust aerosol transportation, the weather condition and pollutant characteristic that influenced air quality of Shijiazhuang on April 15^th, 2015 were analyzed. The HYSPLIT-4model was applied to analyze the back trajectories of dust aerosols. The ground-based micro-pulse Lidar and CE-318sun photometer measurements were used to study the vertical distribution of dust particles and its optical properties variation. In addition, it was compared with another case with strong wind but non dust aerosol deposition. The dust deposition effect on extinction coefficient was discussed. And the contribution of dust deposition to surface PM₁₀ concentration was evaluated. The results indicated that the major factor of rapid increase PM₁₀ concentration in Shijiazhuang was due to the long-distance transportation and deposition of dust particles from Mongolia by the direction of northwest. Dust deposition had an important contribution to both extinction coefficient and PM₁₀ concentration. The rapid dust aerosol disposition was consistent with cold front movement and cold air sinking over Shijiazhuang region. The whole process of dust transportation and disposition had been monitored by the micro-pulse Lidar. It was found that the dust particles mainly distributed on the height of 1500m to 3000m before sinking, where the extinction coefficient increased with the altitude. The process from dust transportation to deposition lasted long time, which could be regarded as one strong alarm signal for dust pollution. When the dust particles arrived over Shijiazhuang region, the aerosol optical depth, turbidity, and particle size showed larger values and the visibility decreased exponentially with the aerosol optical depth.