Measurements Of Aerosol Radiative Properties Over Lanzhou

The atmospheric aerosol plays a crucial role in the global and regional climate change by its direct, indirect, and semi-direct effect. Due to the inhomogeneous temporal and spatial distribution of aerosol it has significant uncertainties in the research of aerosol radiative effect, especially for the dust aerosol, but it has no doubt that the study of aerosol radiative properties makes significant scientific senses, In the semiarid area of northwest China with special surface underlying, the aerosol observation in long-term and continuity is one of the key and fundamental elements in the study of the aerosol impacts on climate change.The vertical distribution and temporal evolution of aerosol over Lanzhou are analyzed using the data of micropulse lidar CE370-2 and depolarization lidar L2S-SMâ…¡at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Then the thesis presents the variation properties of aerosol scattering coefficient, absorption coefficient, and single scattering albedo using the measurements of nephelometer, aethalometer, multi-angle absorption photometer, PM10 particulate monitor et al.. Finally, a numerical simulation of the atmospheric boundary meteorological conditions and dust aerosol radiative properties over Lanzhou during a dust storm is carried out using the WRF+ABL+LOWTRAN7 models system. In all, some valuable results are retrieved, which would be the references for the numerical simulation of aerosol radiative effect and improve the radiation schemes in the atmospheric numerical models. The work surely has important scientific senses and values. The main results are as follows.(1) Statistic analysis of micropulse lidar CE370-2 observation since 2005 to 2008 shows that the maximum aerosol optical depth (AOD) appears in November and December, and AOD in March and April are some bit large, AOD is larger in winter and spring than in summer and fall, which is mainly determined by the conditions of local atmospheric diffusion and pollution emissions. The frequency analysis presents that the AOD mostly ranges around 0.3. As to the vertical distribution of aerosol over Lanzhou, it is mainly concentrated below 2 km height, and the aerosol extinction coefficient decreases with height.(2) The dust aerosol is mostly distributed under 2 km height, and the dust aerosol extinction coefficient decreases with height. The case study shows:In the dust aerosol layer, the aerosol extinction coefficient and relative humidity have the similar variation trends; It has linear correlations among PM10 concentration, aerosol scattering and extinction coefficients, and the correlation coefficient between PM10 concentration and aerosol scattering coefficient, between PM10 concentration and extinction coefficient, between extinction coefficient and scattering coefficient is 0.98 0.94 and 0.96 respectively.(3) Using the data of depolarization lidar L2S-SMâ…¡, the depolarization ratios of aerosol and cloud are analyzed. The depolarization ratios of cloud, ice, and dust aerosol are larger than anthropogenic aerosol. The aerosol depolarization ratio is below 0.25, while that of the cloud and ice mostly range around 0.3.(4) The black carbon (BC) mass concentration and absorption coefficient are analyzed using the measurement of aethalometer AE-31 in 2009. The BC mass concentration at 7 wavelengths have the similar variation trends, and the BC mass concentration of 370 nm is largest, while the BC mass concentration of 950 nm is the smallest. As to the diurnal evolution of BC mass concentration, the maximum appears at 08:00 and 12:00 respectively in the daytime of summer and fall, and winter and spring,22:00 in nighttime. The minimum appears at 16:00. The monthly average of BC concentration's variation shows the U distribution. It decreases since January till the minimum in May, then increases and reaches the maximum in December. It also presents that the BC mass concentration is larger in winter and spring than in summer and fall. As to the BC absorption coefficient, it has the similar variation trend with that of BC mass concentration.(5) Using the data of aethalometer AE-31 and multi-angle absorption photometer (MAAP) 5012 since August to November 2009, the comparison between two measurements presents a good linear correlation. The correlation coefficient between the retrievals of MAAP5012₁35 and MAAP5012₁36, between the retrievals of MAAP5012₁35 and AE-31, and between the retrievals of MAAP5012₁36 and AE-31 is 0.96,0.91 and 0.92 respectively.(6) The frequency distribution analysis of single scattering albedo (SSA) over Lanzhou and Zhangye are carried out using the data of 2008 China-US joint dust storm observation experiment. Over Lanzhou, the SSA of 450 and 550 nm have the similar frequency distributions, and the maximums frequency of SSA at 450 and 550 nm appear at 0.7, while 0.5 for the SSA of 700 nm. As to the SSA frequency distributions over Zhangye, they show similar frequency distributions at 450,50, and 700 nm, and the maximums appear at 0.8.(7) Using the numerical simulation platform of WRF+ABL+LOWTRAN7, the atmospheric boundary meteorological conditions and dust aerosol radiative properties are presented. During the dust storm, the west wind is prevailing in most simulation distract. In the north of simulation area, it has upward motion, as the development of dust storm the downward motion is dominated.The distribution of potential temperature has a good agreement with that of terrain, higher potential temperature is located on higher terrain and the lower seats on the valley. As to the relative humidity, it is opposite to that of potential temperature.The dust aerosol has warming effect in daytime, the temperature increases by 0.39℃. In nighttime, it presents cooling effect under 1 km, and the temperature decreases by 0.4℃,and in the layer above 1 km the dust aerosol has warming effect, the temperature increases by 0.35℃. As to the wind conditions, the dust aerosol increases the wind speed by 0.57 m/s in daytime. In nighttime, the wind speed decreases by 0.56 m/s below 1 km, and increases by 0.47 m/s above 1 km.