气溶胶辐射效应对边界层结构及夹卷特征影响的观测分析

From December 22, 2017 to January 18, 2018, unmanned aerial vehicles equipped with temperature, humidity and particulate matter concentration detectors were used to conduct intensive observations on the vertical structure of the atmospheric boundary layer under the condition of haze pollution in Nanjing. By comparing the differences in the vertical structures of temperature, humidity and PM2.5 (particulate matter with a diameter less than 2.5 micrometers) concentrations under different haze pollution conditions, combined with the ground heat flux, 2-meter air temperature, relative humidity, wind and some chemical quantities (such as ozone, PM2.5), the impact of aerosol radiative effects on the boundary layer and entrainment process was quantitatively evaluated. The analysis shows that haze or aerosol weakens the solar radiation reaching the surface, reduces the surface sensible heat flux, delays the development of the boundary layer, increases the stability of the near-surface atmosphere, reduces the height of the boundary layer, and aggravates the haze pollution. Haze pollutants accumulate at the top of the mixing layer, resulting in the maximum change in PM2.5 concentration occurring at the top of the boundary layer rather than in the near-surface layer. The aerosol radiative effect has an important impact on the entrainment characteristics and their characteristic parameters. When the haze concentration increases, the thickness of the entrainment zone increases; the dimensionless entrainment velocity no longer conforms to the -1 power function relationship with the convective Richardson number, which is consistent with the results of large eddy simulation. This study further points out that in order to improve the numerical prediction level of weather and air quality under the condition of heavy haze pollution, the impact of aerosol radiative effects on the boundary layer and entrainment parameterization must be considered.

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、湿和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，风及一些化学量（如臭氧，PM2.5），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-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。