激光雷达遥感地表气溶胶消光吸湿因子及其对波长的依赖特性

Remote Sensing Aerosol Extinction Hygroscopic Growth Factor and Its Wavelength Dependence Using Lidar

介绍了一种在开放大气环境下、利用水平探测的双波长-偏振米氏散射激光雷达遥感地表气溶胶消光吸湿增长因子的新方法。在激光雷达垂直观测气溶胶吸湿性质相关研究报道的数据筛选方法的基础上,利用消光系数与实测相对湿度(RH)之间的强相关性,以及实测的粒子质量浓度和粒子退偏振比的变化规律作为判据,说明吸湿增长作用是引起地表气溶胶消光系数增大的主要原因。相比于激光雷达垂直方法观测气溶胶吸湿性质,该筛选过程更加严格地约束了激光雷达水平观测吸湿性质的筛选判据,且对气象条件的约束相对简单。利用筛选得到的有效数据,计算得到气溶胶消光吸湿增长因子,并分析其对波长的依赖特性。观测结果表明,在开放大气条件下,合肥地区粒子谱分布可能会出现单模态、双模态甚至多模态的复杂情况,导致Angstrom波长指数与相对湿度之间的变化规律表现为正相关、负相关和不相关3种结果;同样也导致短波的气溶胶消光吸湿增长因子弱于、等于或强于长波的气溶胶消光吸湿增长因子的多样性现象。

A new method of using two-wavelength Mie-depolarization lidar for remote sensing extinction hygroscopic growth factor of aerosol near ground layer under varying conditions of relative humidity（RH）is proposed.Based on the algorithm used in lidar vertical aerosol hygroscopic growth observations,lidar horizontal measurements data is researched using strong correlation between extinction coefficient and RH,and the measured particle mass concentration going along with the decrease of depolarization ratio is used as a criterion,which proves that the hygroscopic effect of aerosol is the main cause of the extinction coefficient increment.Compared to the lidar vertical aerosol hygroscopic growth observations method,the proposed method has the advantage of the raising data selection criterion and simple meteorological conditions.Extinction hygroscopic growth factor can be calculated using valid data in lidar database,and its wavelength dependence is analyzed.Observation results at Hefei district show that,in various natural atmospheric environments,unimodal,bimodal and even multimodal aerosol distributions may exist.As a result,positive correlation,negative correlation and irrelevance between RH and Angstrom exponent can be observed,and hygroscopic growth factor at short wavelength can be weaker than,stronger than or equal with that at long wavelength.