An Observation Study of the Scattering Properties of Aerosols over Shangdianzi, Beijing
北京上甸子秋冬季大气气溶胶的散射特征

Aerosols play a very important role in the climate system through its direct and indirect effects on the radiation forcing.The scattering coefficient of aerosols is an important optical parameter representing the scattering capability of aerosols and affecting its behavior on radiant transfer.Foreign scientists have begun observation experiments of the scattering properties of aerosols since the 1980s.However,the same experiments are late in China,which leads to extremely lack the observation data of scattering properties.In order to understand the radiative properties of aerosols in North China,a measurement was carried out during October to December 2003,in Shangdianzi regional Global Atmosphere Watch(GAW) station,which is located in the rural area of northeast Beijing city with a distance of 110 km from the downtown.The scattering coefficient was measured by a Model 9003 nepholometer(Ecotech,Australia).The zero check was done daily by using the filtered air and the span check/calibration done biweekly by using pure F134a gas,following the recommendations of manufacture.The heated inlet was used to insure that the scattering coefficient was measured under the condition that relative humidity was lower than 60%.The 5 minute data of scattering coefficient were carefully checked and then reduced to hourly dataset.Hourly PM2.5 mass concentration data were obtained by using a TEOM instrument(Model 1400a,R&P USA) only in December.Additionally,hourly meteorological data were obtained by an automatic weather station system at site through whole three months.The results of measurement showed that the scattering coefficient of aerosols over Shangdianzi was very variable with the hourly maximum value up to 1800 Mm-1 and the hourly minimum value as low as below 10 Mm-1.The averaged scattering coefficient for whole experiment period was 179.7 Mm-1,with the standard deviation of 253.2 Mm-1.The scattering coefficient also varied with a clear diurnal pattern,high at night and low in daytime,which showed obvious influences of local inversion at night.The mean scattering coefficient in different weather conditions showed obvious differences.The scattering coefficient in overcast days was significantly higher than that in fine days.This difference is considered as the result of combination of changes in boundary layer convection and local wind flow pattern of two kinds of weather condition.A good correlation between scattering coefficient and PM2.5 mass concentration was found with high coefficient as 0.93.Because of the location of Shangdianzi relative to Beijing urban area,the scattering coefficient of aerosols increased dramatically when the wind flows were from southwest.On the other hand,low scattering coefficient values often appeared in the periods of northeast wind flow.This indicates the transportation of pollutants from mega city like Beijing has significant influences on the properties of aerosols of the regional background.