• 关键词：边界层结构  小风层厚度  风廓线雷达  激光雷达  微波辐射计  佛山

• 基金项目：国家重点研发计划课题（No.2016YFC0203305）；国家自然科学基金重点项目（No.41630422）；国家科技支撑计划（No.2014BAC21B00）和佛山市气象局课题

• 李浩文
• 中山大学大气科学学院, 广州 510275

• 张阿思
• 中山大学大气科学学院, 广州 510275

• 步巧利
• 广东省佛山市气象局, 佛山 528000

• 董国业
• 广东省佛山市气象局, 佛山 528000

• 炎利军
• 广东省佛山市气象局, 佛山 528000

• 祝薇
• 中山大学大气科学学院, 广州 510275

• 范绍佳
• 中山大学大气科学学院, 广州 510275

• 摘要：2015年12月21-23日，广东珠三角佛山地区出现了一次PM_2.5重污染过程.利用佛山地区顺德、禅城、三水3个站点风廓线雷达、激光雷达和微波辐射计观测资料，结合地面气象观测数据和污染物浓度数据，分析研究了这次重污染过程的形成机理.结果表明：①形成这次污染过程的主要原因是近地层偏南风和偏北风对峙导致水平风速减小，大气水平输送能力变差；持续时间长且强度达到3℃·km^-1的强逆温抑制了污染物的垂直扩散；800 m以下超过90%的高相对湿度造成气溶胶粒子吸湿增长显著.②持续时间长且比较深厚的小风层是造成这次污染过程的直接原因，小风层厚度是预报空气质量变化的较好工具.与地面风速相比，PM_2.5浓度与小风层厚度的相关系数最多能提高0.36，且具有较长的预报时效.佛山地区小风层的风速阈值为3.8 m·s^-1.③这次污染过程存在两种不同的污染形成机制，污染前期（21-23日中午）主要以本地污染物累积为主，污染后期（23日下午）下风向地区（三水）的污染主要是受上风向地区（顺德和禅城）的污染输送影响.

• Abstract：Foshan experienced a heavy air pollution episode during December 21 to 23, 2015. With the data measured by wind profile radar, laser radar and microwave radiometer in three sites (Shunde, Chancheng and Sanshui)and the ground meteorological observation data, the formation mechanisms of this episode are analyzed. The results show that three reasons are collectively responsible for this episode. The interaction between southerly and northerly winds decreases horizontal wind speed and weakens the horizontal transport ability, long duration of strong inversion with intensity up to 3℃·km^-1 restrains the vertical diffusion of pollutants, and high relative humidity below 800 m above ground level leads to significant hydroscopic growth of aerosol particles. The long duration of deep small wind layer is the direct reason for this pollution process. In comparison with ground-level wind speed, the depth of small wind layer is a better factor for forecast of air quality change. Its correlation with PM_2.5 concentration is improved by up to 0.36 with a longer predictability. The threshold of small wind layer wind speed is 3.8 m·s^-1 in Foshan area. There are two different pollution formation mechanisms during this process, i.e. local pollutant accumulation in the early stage (December 21 to 23) and regional transport from upwind (Shunde and Chancheng) to downwind (Sanshui) areas in the late stage (after December 23 noon).

• Key words：atmospheric boundary layer structure  small wind layer thickness  wind profile radar  laser radar  microwave radiometer  Foshan

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