基于机载观测资料订正雷达比及其垂直分布特征

雷达比是激光雷达反演气溶胶光学特性的重要参数和影响因素。利用北京地区2016年一次清洁过程（12月10日）和两次污染过程（11月15～18日和12月16～19日）的微脉冲激光雷达、机载浊度计和黑碳仪以及多种地基观测设备，综合研究基于飞机观测订正雷达比的方法及其分布特征。清洁过程地面PM_2.5浓度低于40 μg m?3；污染严重时期的PM_2.5均高于150 μg m?3且能见度低于5 km，污染过程1存在高空传输的特征。研究结果表明相较于采用单一的柱平均雷达比，利用本文方法获得的雷达比垂直廓线反演得到的气溶胶消光系数和光学厚度更接近原位跟踪观测，精度均有提升。基于此方法获得的雷达比在污染发展不同时期垂直分布差异较大，主要分布在19～76 sr之间，清洁时期雷达比较小且垂直分布差异不大。污染过程1雷达比随高度波动增加至边界层顶（19～45 sr）；污染过程2严重期边界层内雷达比随高度由70 sr降低到20 sr；边界层以上均呈现小幅波动变化。边界层内雷达比垂直分布与气溶胶来源特别是高空气溶胶传输有密切联系，混有沙尘的区域传输显著提升了所在高度的雷达比值。边界层以上雷达比受少量大粒子或者强吸收性的气溶胶粒子的影响波动变化。边界层内消光系数增大时雷达比呈增加趋势；当相对湿度高于40%，边界层内雷达比随相对湿度增加而增大。

Correction of Lidar Ratio and Its Vertical Distribution Characteristics Using Aircraft Observations

The lidar ratio (LR) is an important parameter and impact factor for the retrieval of aerosol optical properties using micro-pulse lidar. We analyze the vertical LR retrieved by the method of correcting micro-pulse lidar with aircraft observation using multiple-observation equipment during one clean case (December 10, 2016) and two pollution cases (November 15–18, December 16–19, 2016) in Beijing. PM_2.5 concentration was lower than 40 μg m?3,while PM_2.5 concentration was higher than 150 μg m?3, and visibility was lower than 5 km during the severe-pollution period. The first pollution case was characterized via high-altitude transportation. The vertical extinction coefficient profiles and aerosol optical depth (AOD) obtained by the iterative algorithm using the LR values were closer to the in-situ observation than those obtained by the single column average value. LR obtained from this method primarily varied between 19 and 76 sr in different periods. The results showed a small LR value and insignificant differences in vertical distribution during the cleaning period, and LR increased in height from 19 to 45 sr in the boundary layer during the first pollution case. During the second pollution case, LR presented little variation during the pollution-development period and later decreased in height from 70 to 20 sr at the boundary layer under the severe-pollution period, while there were slight fluctuations above the boundary layer. The vertical distribution of LR along the boundary layer is related to the source of aerosols, especially the regional transportation in the high layer, and regional dust transportation may significantly increase the LR. LR fluctuates due to the influence of large particles or strong absorbing particles above the boundary layer. The results showed that LR increased with the increase in the extinction coefficient at the boundary layer as well as relative humidity (RH) when RH was higher than 40%.