Preliminary Studies On Radiative Properties Of Dust Aerosol In North China

Atmospheric aerosol plays an important role in both through the scattering and absorption of incoming solar radiation (the so-called direct effect) .And also it effects on size, concentration and lifetime of cloud droplet, leading to change of earth-atmosphere radiation balance (indirect effect).By using the direct solar radiation data measured by CE-318 sun photometer in Inner Mongolia during the period between June 2002 and May 2003, the aerosol optical thickness (AOT) and size distribution were retrieved by extinction method. The radiative properties including scattering efficiency, single scattering albedo (SSA), extinction coefficient were analyzed.The results show that there is a significant variation of temporal-spacial distributions of AOT. The highest AOT appears in spring[AOT(λ=440nm)=0.78] with the lowest in winter[AOT(λ=440nm)=0.13]. The AOT in Ejin Qi is always the highest and average AOT(λ=440nm) is 0.34. The lowest one is 0.29 in Dongsheng. However, it shows a significant discrepancy in different weather conditions. The aerosol is steady and consistent in the clean weather. The evolution of AOT is relatively steady, while in the dust weather, the AOT increases extremely and AOT(λ=440nm) is about 4. There are four patterns of daily variation of AOT: (1) the AOT is high in morning and low in evening, about 24%²9%;(2) the low AOT is in morning and the high one is in evening, about 35% ³6%;(3) the AOT presents a peak at noon, is about 21 %³3%;(4) the relatively steady pattern, is about 4%^The scattering efficiency and extinction efficiency of dust aerosol both appear a high value when radii is 0.1-1.0μm. The value is about 4. And the position of high value is in the direction of bigger radii when the channel λ₁ increases. The absorbing efficiency increases with the radii increases and approaches 1. The highest SSA is about 0.97 when radii is 0.1μm— 1.0μm. The aerosols with radii range from 0.1μm— 0.4μm contributed significantly to the total extinction coefficient. The highest is β_e(440) = 0.36 km^-1. The highest extinction capability is for 440nm wavelength. For the wavelengths longer than 440nm, extinction capability is lower. The aerosol extinction parameters are very sensitive to the imaginary part of complex refractive index. A small variation of imaginary part could lead to a deep effect on total extinction.The aerosol size distribution satisfies Junge distribution basically and appears obvious peak values (r=0.3um, 0.6um, l.Oum), are about 108cm"2-um"1, 107cm'2-uxn"] and 106cm'2-um'1. However, it shows a significant discrepancy in different weather conditions. Large dust particles and giant dust particles remarkably increase in dust weather. The aerosol number concentration in dust weather is about one magnitude larger than that of in clean weather. And it is also larger in spring (8.22x109 cm^-um'1) than that in winter (1.17><109 cm^-um'1) but within one magnitude. And it is about 2.07x109 cm^-um'1 in summer and autumn.