Aerosol Optical Depth Observations In Lanzhou

Atmospheric aerosol plays an important role in influencing and adjusting the global climate, is considered to be one of the important factors that affect climate change. Usually due to such characteristics as the low concentration, short lifetime and great changes in time and space, complicated sources, atmosphere aerosol be researched in climate change as the biggest uncertainty factors。Two CE318sun photometers were used in Lanzhou city and Gaolan Mountain nearby to observe the Aerosol Optical Depth, the turbidity coefficient and the wavelength exponent in2006, to analyze the correlation between meteorological elements and aerosol parameters and the characteristics of changes over time. In addition, we analyzed the relative change of aerosol optical parameters in the Lanzhou city and Gaolan Hill, and discussed the influence of terrain conditions on aerosol concentration. Considering the insufficiency of the Ground-based observations, we analyzed the feasibility of applying the MODIS satellite data to inverse Aerosol Optical Depth in Lanzhou city. The main conclusions are as follows:(1) According to the working principle of CE318sun photometer, we put forward the insufficiency of Langley method be used in Lanzhou city, and corrected calibration constants on the basis of the traditional, the revised InVo had better correlation with m.(2) In the correlation analysis of AOD and influence factor, we found that the atmospheric stability parameter is the main factor affecting the spread of Lanzhou urban AOD, and is positive correlation. And the ground wind speed has a little effect on AOD, may be the Lanzhou is surrounded by hills cause the ground is given priority to with no wind or weak wind all year long。In the fitting process, the ground wind speed and atmospheric stability parameters have significant influences on the Angstrom wavelength exponent. Atmospheric stability parameter is positive correlation and the ground wind speed is negative correlation with a. But the correlation between the Angstrom turbidity coefficient and ground wind speed and atmospheric stability parameters is poor.(3) The diurnal variation of the aerosol optical parameters has obvious regularity, the change of the Lanzhou urban has obvious different with the Gaolan Hill. In urban,AOD is given priority to with peak type structure, accounting for56%of the total number of days; Steady type is also a main AOD change type, accounting for27%; Other types is complicated because the weather system of transit, accounted for17%. In Gaolan mountain, AOD is divided into two important types of peak type accounted for59%of the total number of days, and valley type accounted for25%。The diurnal variation of the Angstrom wavelength exponent is relatively simple, the urban is given priority to valley type, the top of the mountain is given priority to with peak type, were accounting for72%and81%of the total number of days respectively. The Angstrom turbidity coefficient, urban area can be categorized into peak type and steady type, accounting for60%and26%respectively; The top of the mountain can categorized into peak type and valley type accounting for48%and36%respectively.(4) The change of the average monthly AOD is significant in Lanzhou city in2006. The AOD is highest in December and the lowest in November, and in accordance with the distribution of the seasons, is the highest in winter, followed by spring, autumn minimum. The Angstrom wavelength exponent analysis found that dust particles is the main component of the aerosol.And the largest is in December, which related with the heating in winter., and the lowest in April, which related with sand and dust weather. The Angstrom turbidity coefficient is highest in April and the lowest in November, and according to the season that is the highest in spring, followed by winter, autumn minimum. The annual average is greater than0.2that illustrate the air quality is poor in Lanzhou city. The diurnal variation of the AOD and The Angstrom turbidity coefficient can be classified as peak type in550nm channel, and the numerical value is smaller in evening than in morning. The diurnal variation of Angstrom wavelength exponent can be classified as valley type, and the aerosol particles is more smaller in the morning and evening.On seasonal average, there is not much difference of Aerosol Optical Depth between two seasons over Gaolan Mountain. In Lanzhou city, the optical depth is much larger in Winter than in Spring, mainly for the heating from coal. The contributions of aerosol near the surface layer to the total optical depth are about48%in spring and60%in winter. The numerical value of Angstrom wavelength exponent is greater in mountain than in urban, the daily variation of Angstrom wavelength exponent is more stable in urban than in mountain. The value in mountain is influenced by the urban aerosol and ambient aerosols, and in downtown is influenced by primarily from a local emission source, especially in winter. Through the analysis of the turbidity coefficient, we find that turbidity coefficient is influenced by aerosols dust particles more significantly, and AOD is influenced by soot particles more significantly.(5) The inversion values of CE318photometer in most of the time is greater than the MODIS, the change rule there is a certain similarity. Besides lack representative due to less data in winter, the correlation analysis and linear fitting effects of the other three seasons and vary widely that illustrate the application of MODIS inversion method of aerosol in Lanzhou city has strict time limitations. The feasibility of the Aqu-MODIS data inversion AOD is larger in summer, but Terra-MODIS in spring. Satellite data inversion result is bad in other season, and the inversion method has yet to be improved.