| Aerosol as an important component of the atmosphere has an increasingly profound and lasting impact on the earth-atmospher system.The Loess Plateau as a typical semi-arid region emits a large number of dust particles each year.Therefore it is significant to obtain the spatial and temporal distribution of the aerosol about annual,seasonal,and monthly changes for estimating the effects of aerosol on climate change.The observational data of the Semi-Arid Climate and Environment observatory of Lanzhou University(SACOL)was used to analyze the optical properties of the aerosol.We improved the existing Klett-Fernald lidar algorithm,and the multi-scale cloud recognition algorithm had been added,which had lower requirement about signal-to-noise ratio than previous studies.The main results were as follows:(1)In this paper,the frequency distribution of aerosol at SACOL was analyzed using a dual-wavelength lidar,a sun photometer and an aethalometer.We comprehensively described the optical properties of the aerosol according to the depolarization ratio,AOD,effective radius and black carbon mass concentration,and discussed the main source of polluted particles and their causes in each season at SACOL.This study found that the annual column-averaged depolarization ratio was0.12±0.08,and the value ranged from 0 to 0.15.The annual average effective radius was 0.53±0.21?m,and the value ranged from 0.3 to 0.6?m.The annual average AOD was 0.28±0.27,and the value ranged from 0 to 0.4.The annual average mass concentration of black carbon was 1.63±1.25?g/m~3,and the value ranged from 0 to2?g/m~3.The vertical distribution of the extinction coefficient varied greatly between 0to 3km,with rising firstly from the ground and then decreasing rapidly after reaching a maximum that the value was about 0.1km~-11 at approximately 1km.The depolarization ratio changed smaller than extinction coefficient between 0 to 3km,with the values mainly concentrated on 0.15.(2)The column-averaged depolarization ratio in spring,summer,autumn and winter were 0.17±0.1,0.09±0.07,0.09±0.07,and 0.12±0.08,respectively.The overall trend of depolarization ratio increased from January and then decreased after reaching the peak of 0.2±0.09 in April.The lowest depolarization ratio was 0.08±0.07 appeared in September.The average effective radius in spring,summer,autumn and winter were 0.63±0.24,0.42±0.13,0.44±0.12,and 0.59±0.24?m,respectively.The overall trend of effective radius increased slowly from January and then decreased after reaching the peak in March(0.63±0.21?m)and April(0.63±0.23?m).The lowest effective radius was 0.4±0.09?m in August.The average AOD in spring,summer,autumn and winter were 0.38±0.33,0.21±0.22,0.20±0.20,and 0.27±0.24,respectively.The highest AOD appeared in March and April,with values of 0.42±0.35 and0.42±0.34,respectively.The lowest AOD was 0.19±0.18 in June.The average mass concentration of black carbon in spring,summer,autumn and winter were 1.03±0.76,1.2±0.7,1.93±1.28,and 2.35±1.56?g/m~3,respectively.The highest mass concentration of black carbon was 2.37±1.12?g/m~3 in January and the lowest mass concentration was 0.94±0.6?g/m~3 in April.The extinction coefficient in spring was larger than the other three seasons in the range of 0.5-2km,and the highest value was about 0.15km~-11 near 1km.The characteristics of the extinction coefficient in autumn and winter were similar,which decreased with the height.The extinction coefficient in winter was also large because of the coal burning.The largest vertical depolarization ratio distributed in spring and followed by the winter.The vertical distribution of depolarization ratio in summer was similar to that of autumn.(3)A dust storm was observed at the Semi-Arid Climate and Environment observatory of Lanzhou University(SACOL)using a dual-wavelength lidar and an aethalometer from 16 March to 22 March 2010.There were two main sources of this dust storm that were the Taklamakan Desert and the desert closed to Dunhuang.The wind direction of this dust process was dominated by the wind in the northerly direction.The proportion of northerly winds exceeded 10%,and the maximum wind speed in the northwest reached 7m/s.After the arrival of the dust storm,the lidar backscattered signal increased suddenly;the depolarization ratio ranged from 0.2 to0.4;the?ngstr?m exponent ranged from 0.5 to 1.0;the average of AOD was 0.6.During the dust storm,the dominant particle was non-spherical and coarse-mode,the particle size mainly concentrated in 2?m.An aethalometer was used to measure the aerosol absorption coefficient as well as absorptive aerosol mass concentration.The average mass concentration of absorptive aerosol was 1.3?g/m~3 during the dust free period but increased to 1.8?g/m~3 during the dust storm.In addition,the peaks of the absorptive aerosol mass concentration mainly occurred at around 08:00 and 20:00.The trend of the aerosol absorption coefficient was similar to that of mass concentration,and the aerosol absorption coefficient significantly increased during the dust storm. |
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