Lidar Measurement Of Atmospheric Aerosol Radiative Properties Over Lanzhou

The aerosol properties were measured systemically by a lidar in Lanzhou for the first time. The paper combined the Fernald method and the Collis slope method and developed a new data processing method based on the instrument and the local environment conditions. The aerosol extinction coefficient profile was retrieved through the lidar observation data, and the daily and seasonal variations of the aerosol extinction coefficient were analyzed. The main contents were as follows.(1) A new method to process the lidar data based on the Fernald method which was considered from the instrument and the local environmental conditions was developed, and the new method built another way to set the calibration altitude as well as the boundary condition.Applying the method, the AOD (aerosol optical depth) by two different schemes (set S₁ as 20&15, and as 30, respectively) was calculated, and then compared theresults with the AOD derived from L97 sunphotometer, it showed that the former scheme was more reasonable, and that was the very one which we adopted.(2) By processing the lidar data, the characteristics of aerosol extinction coefficient vertical distribution and evolution were revealed primarily.A. Typical day characteristicsThe trends of the low level aerosol extinction coefficient was agreement with that of the AOD, both of them reached the maximum at 1200 (Beijing Time), then declined, and reached the minimum at 2000, and finally rose a bit at midnight.The trend of the low level aerosol extinction coefficient was in accord with that of visibility.The aerosol concentration was mainly distributed in low level (below 500¹000m), and it decreased greatly with altitude.B. Seasonal characteristicsIn summer, fall, and winter, the low level mean aerosol extinction coefficient usually reached the maximum at 1200, then decreased gradually, but finallyrebounded slightly at midnight, so did the mean AOD.The maximum of low level mean aerosol extinction coefficient occurred in winter, and the minimum occurred in summer and so did the mean AOD.The mean aerosol extinction coefficient decreased rapidly with altitude in fall and winter, but the trend was not significant in summer.C. Mean daily characteristicsThe low level mean aerosol extinction coefficient reached the maximum in winter, minimum in summer at 1200, 1600, 2000 and 0000;but the maximum of the mean aerosol extinction coefficient appeared in summer, the minimum in winter above 1.5km level.D. A snowstorm procedureThe low level aerosol extinction coefficient was comparative large before the snowstorm procedure, with the AOD of about 0.408 between 0.195⁵km level;after the snow, the low level aerosol extinction coefficient decreased significantly, with the AOD of about 0.205 between 0.195⁵km level.This study would help to understand deeply the optical properties of aerosol, and it would be of benefit to the researches of aerosol radiative forcing and climate response.