摘要:2017年12月22日至2018年1月18日利用无人机携带温、湿和颗粒物浓度探测仪对南京地区灰霾污染条件下大气边界层垂直结构开展加密观测。通过比较不同灰霾污染条件下温度、湿度和PM2.5（直径小于2.5微米的颗粒物）浓度的垂直结构差异，结合地面热通量、2米空气温度、相对湿度、风速、风向及主要大气污染物（如臭氧和PM2.5）浓度，定量评估了气溶胶辐射效应对边界层和夹卷过程的影响。分析表明，灰霾或气溶胶削弱到达地表太阳辐射，减小地表感热通量，延迟边界层发展，增加近地层大气稳定度，降低边界层高度，并加重灰霾污染。灰霾污染物在混合层顶处累积，导致PM2.5浓度最大变化出现在边界层顶部而不是近地层。气溶胶辐射效应对夹卷特征及其特征参数有重要影响。灰霾浓度升高时，夹卷区厚度增加；无量纲化夹卷速度随对流理查逊数的变化不再符合负1次方幂函数关系，与大涡模拟结果一致。本研究进一步指出，为提高重霾污染条件下天气和空气质量数值预报水平，必须考虑气溶胶辐射效应对边界层和夹卷参数化的影响。
关键词:气溶胶辐射效应/
边界层/
夹卷/
无人机探测
Abstract:An unmanned aerial vehicle (UAV) equipped with portable instruments was used to measure the vertical profiles of temperature, specific humidity, and particulate matter under different haze-polluted weather conditions in Nanjing from December 22, 2017 to January 18, 2018. The study aimed to assess the impact of the aerosol radiative effect on the atmospheric boundary layer (ABL) and the entrainment zone structures as well as their evolution on days with heavy haze pollution and other days with good air quality. The vertical profiles of the potential temperature, water vapor, and PM2.5 concentrations were obtained through detailed analyses of the UAV-measured vertical profiles and surface observations, including the surface heat flux, 2-m air temperature, specific humidity, wind speed, wind direction, and major air pollutants concentration (e.g., O3 and PM2.5) under different air pollution conditions. The results indicate that aerosols reduce the amount of surface-reaching solar radiation and the surface sensible heat flux, postpone the development of the ABL, enhance the atmospheric stability near the surface, decrease the ABL height, and exacerbate air pollution. The maximum concentrations of PM2.5 and the largest increase rate were observed at the top of the ABL rather than near the surface. Furthermore, the aerosol radiative effect was found to have an important impact on entrainment and its characteristic parameters. The depth of the entrainment zone increased with increasing surface PM2.5 concentrations. The entrainment rate normalized with convective velocity did not follow a negative?1 power function with the convective Richardson number under heavy haze or PM2.5 pollution conditions, which is consistent with the findings of large-eddy simulation studies. These results indicate that the aerosol radiative effect must be included in ABL and entrainment parameterization schemes to improve numerical predictions of weather and air quality under heavy pollution conditions.
Key words:Aerosol radiative effect/
Planetary boundary layer/
Entrainment/
Unmanned aerial vehicle (UAV)
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