北京春季强沙尘过程前后的激光雷达观测

利用激光雷达、PM_2.5和地面气象要素等综合观测资料,分析了北京地区2012年3月30—31日的强沙尘过程前后的天气形势和PM_2.5的污染特征,反演了雷达探测期间得到的消光系数,探讨了沙尘过程中气溶胶的时空分布特征及输送特征. 结果表明:沙尘过境时,地面风速最大达到6m/s,沙尘沉降时ρ(PM_2.5)增至289μg/m3,相对湿度和能见度明显降低,大气低层逆温和近地面风速等气象条件对沙尘影响地面的时间和程度起到了重要作用；沙尘层雷达反演的气溶胶消光系数最大为0.96km-1,偏振比最大为0.4,近地面消光系数变化与地面ρ(PM_2.5)变化规律吻合较好,其探测可以精确反映不同天气形势下气溶胶的垂直结构和时空变化信息；高空输送至北京的沙尘以粗颗粒物为主,细粒子主要来源于本地及周边地区细粒子源；西北方向的内蒙及外蒙地区沙尘输送是导致此次北京强沙尘过程的主要原因. 

Lidar Detection of a Sand-Dust Process at Beijing in Spring

A sand-dust process in Beijing was monitored based on a Lidar system, PM_2.5 and conventional meteorological observation instruments on March 30th and 31st, 2012. The aerosol extinction coefficient was retrieved during this process. The vertical structure and transport characteristics of sand-dust aerosol and the concentration of PM_2.5 were analyzed. The results indicated that wind speed increased to 6m/s and the concentration of PM_2.5 at land surface increased to 289μg/m3, when the sand-dust process sustained; meanwhile, the relative humidity and the appearance of haze significantly decreased. The meteorological conditions such as inversion of lower atmospheric and wind speed near the ground greatly impacted on the duration and intensity of the sand-dust. The maximum value of extinction coefficient was 0.96km-1, while depolarization ratio was 0.4. There was a strong correlation between the aerosol and extinction coefficient at 400m retrieved from the Lidar data. PM mainly originated from local and surrounding areas of Beijing. Sand-dust from Inner Mongolia Province and outer Mongolia area is the main reason to explain the process.