研究报告
潘亮,吴俊石,张燕燕,汪红斌,许建明.上海早晨边界层的稳定度特征及其对PM2.5峰值浓度的影响[J].环境科学学报,2020,40(4):1351-1360
上海早晨边界层的稳定度特征及其对PM2.5峰值浓度的影响
- The characteristics of the morning atmospheric stability and its impacts on the peak PM2.5 concentration during 2013 to 2017 in Shanghai
- 基金项目：上海市气象局科技项目（No.MS201807，MS201808）
- 作者
- 单位
- 潘亮
- 长三角环境气象预报预警中心, 上海 200030
- 吴俊石
- 宝山气候观象台, 上海 200030
- 张燕燕
- 宝山气候观象台, 上海 200030
- 汪红斌
- 宝山气候观象台, 上海 200030
- 许建明
- 1. 长三角环境气象预报预警中心, 上海 200030;2. 大气科学与卫星遥感安徽省重点实验室, 合肥 230000
- 摘要：PM2.5的峰值浓度一般出现在早晨，这是早晨高排放和低边界层共同作用的结果.早晨的边界层结构对PM2.5峰值浓度及演变具有重要影响，但准确反演早晨较低的边界层高度存在很大困难.基于此，本文以上海为例，采用8：00的L波段气象探空数据，利用高分辨率的垂直风温资料计算总体理查逊数（Rf）来判定早晨边界层的稳定度.研究发现，上海早晨边界层的稳定度具有明显的季节差异，其中，11月、12月和1月基本为稳定边界层结构（SBL），5—8月为对流边界层结构（CBL）.通过分析风温廓线发现，上海冬季早晨SBL存在明显逆温，高度约为100~200 m，平均逆温强度为2.4℃/100 m；而夏季早晨的CBL可发展至400~500 m.早晨PM2.5峰值浓度随Rf的升高明显上升，SBL条件下的PM2.5峰值浓度较CBL条件下偏高约20 μg·m-3.2013—2017年上海早晨边界层的稳定度在春季和冬季呈波动上升的趋势，其中，2016和2017年的上升幅度尤其明显.2016、2017年春季的SBL频数较2013—2015年同期分别偏多12.5%、17.0%，冬季分别偏多10.8%、9.0%，而2016、2017年春季的PM2.5浓度却分别下降11.00%、23.00%，冬季分别下降27.94%和34.38%，表明近几年上海早晨的PM2.5排放强度明显下降.
- Abstract：The peak values of PM2.5 mass concentration usually appear in the morning jointly resulting from the high local emissions and low planetary boundary layer (PBL). The morning PBL structures have great influence on the peak levels and the evolution of PM2.5 concentrations. However the height of a stable or a neutral PBL in the morning cannot be well retrieved with traditional parameters. In this paper, the bulk Richardson number (Rf) was applied to examine the atmospheric stability in the morning using high-resolution radiosonde measurements during 2013—2017 in Shanghai. Observational results suggested that the morning PBL exhibited distinct seasonal variations in Shanghai, presenting stable structures(SBL) in November, December and January, and convective structures(CBL) from May to August. By analyzing the profiles of temperature and wind speed, we found that the morning SBL was associated with obvious inversion layers in winter, locating at altitudes of 100~200 m. In summer, the CBL could develop to an altitude of 400~500 m due to strong solar radiation. The PM2.5 concentrations exhibited significant increase with enhanced Rf in the morning, with peak values in SBL 20 μg·m-3 higher than those in CBL, indicating that a stable PBL was more favorable for the accumulation of local PM2.5. The stability of the morning PBL tended to be enhanced in spring and winter during 2013—2017, exhibiting higher Rf in 2016 and 2017. The frequencies of SBL increased by 12.5%, 17.0% in spring of 2016 and 2017 respectively, and 10.8%, 9.0% in winter of 2016 and 2017 respectively, compared to those in 2013—2015, suggesting more stable PBL structures in the morning. The corresponding peak PM2.5 concentrations decreased by 11.00%, 23.00% in spring and 27.94%, 34.38% in winter respectively, indicating significant emission reductions as a result of the implementation of Clean Air Action in Shanghai.
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