Retrieval Of Lanzhou Urban And Suburb Aerosol Radiative Properties Using Lidar Measurement

Aerosol is a very important factor in research of atmospheric sciences. It impacts the climate, cloud, precipitation and many elements of meteorology. But we know little its spatial and temporal characteristics because of the lack of efficient methods for observation. Now lidar can reinforce this lack. This paper used a CAML^TMCE-370-2 MPL (Micropulse Lidar) which purchased from CIMEL, a French company, observing the aerosol in Lanzhou urban and suburb Yuzhong for a long time. After selecting an appropriate method to retrieve the lidar data, we got the following main results.(1) Fernald method was used to retrieve lidar data, and it was got some changes. We used different scheme to pick up the calibration altitude with 3.5 km of the dividing line, then retrieved the boundary condition with slope method. Lidar data were compared with L97 sunphotometer data for deciding the value of S₁, the extinction-to-backscattering ratio, in different altitudes. The calculating precision was improved by changing the numerical integral scheme.(2) The aerosol extinction coefficient vertical distribution in Lanzhou was retrieved. The aerosol concentrates less than 2km, and reduces with altitude. The daily variation of the extinction is that it decreases to the minimum at night, then increases at morning, and reaches the maximum at noon. The seasonal variation characteristic is that it reduces to minimum in summer, then increases in autumn, and reaches the maximum in winter. The main changing range is between 0.195～2.0 km. The lidar data observed in Lanzhou are compared with that of Yuzhong. The results show evident difference, with the main different range of 0.195～2.0 km.The variation of aerosol extinction coefficient during three precipitation procedures is compared with the variation of water content data detected by microwave profiling radiometer. It is found that the extinction coefficient retrieved from 532nm lidar measurement can be influenced by the water content, and the more important influent factor is relative humidity. It will be very evident when precipitating, and there is much similarity between extinction coefficient vertical distribution and relative humidity vertical distribution. So, when the lidar observation data are used, the influence of water content will be paid more attention. Finally, the dust aerosol extinction coefficient vertical distribution is analyzed. It shows that the dust is mainly concentrated less than 1.5 km. The extinction coefficient during sand dust weather is evident larger than normal circumstance.The paper implicates that the lidar is a very efficient instrument for observing aerosol. We hope that it can promote the research of the aerosol radiative forcing and its climate response through lidar measurement of aerosols vertical distribution property in Lanzhou.