Observational Study On Aerosol Scattering And Absorption Properties In Semiarid Area And A Preliminary Study On Dust Emission Rate

Using integrating nephelometer and aethalometer observations in 2005 2006 measured at the Silinhot Observatory in Nei Mongolia, a study is performed of variation in aerosol scattering and absorptive properties in the semi-arid climate, with the affecting factors investigated. Results show that (1) In autumn - winter, on the whole, the scattering coefficient follows a pattern of dropping and then rising, due to human activities and meteorological conditions locally, the curve of daily mean scattering exhibits an evident bimodal form, with the appearance time and magnitude of the peak and valley varying slightly with season. The coefficient can be a good indication of the strength of sandy weather. The scattering coefficient and mass concentration of PM₁₀ have a high correlation coefficient, the mass scattering coefficientα=0.313 m²/g; There is an exponential relation between the scattering coefficient and the visibility. (2) The concentration of black carbon aerosols is much higher in winter than in spring because of the heating of coal burning in wintering. Precipitation scavenges the particles out of the air through moist deposition. Both in spring and in winter the daily mean follows a remarkable bimodal course. The peak and valley occur about 1 hr earlier than the scattering counterparts. (3) A study was performed of windspeed impacts on the scattering coefficient and BC mass concentration, and found that when the wind speed <3.5 m/s, its increase would substantially dilute the BC scattering coefficient and mass density. (4) Atmospheric visibility calculated from the aerosol scattering and absorptive coefficients is closer to reality; the scattering and absorptive extinctions account, respectively, for 75 and 25% of the total by aerosols in December.Using the dust particle concentration data measured by Wide Range Particle Spectrometer, the dust emission rate,friction velocity and threshold friction velocity over the surface of Zhurihe area was estimated. The result indicated that (1)The value of dust flux was in accordance with the intense of the dust weather. It showed that the dust flux increased when sand and dust weather occurred, and increased with the increasing sand and dust weather intensity. The average dust flux over dust-storm weather and blowing sand weather are 6.0×10^-8 kg·m^-2·s^-1and 4.14×10^-8 kg·m^-2·s^-1, respectively. (2)The friction velocity is almost less than 1 m/s. The relationship between dust emission rate and friction velocity was analyzed, when n is lor 2, the dust flux had the best linear correlation withU)*ⁿ. (3)The threshold frictionvelocity of observed dust diameter was calculated. When the diameter was increased, the threshold friction velocity there is first an ascending then a decline trend. The result observed in this article was prepared for the building of dust flux mode of arid area.