The measurement of aerosol optical properties at a rural site in Northern China

[摘要] Atmospheric aerosols constitute one of the largest sources of uncertainty inthe estimation of radiative forcing for climate. From April 2003 to January2005, in situ measurements of aerosol optical properties were conducted at arural site in Northern China, Shangdianzi Global Atmosphere Watch (GAW)regional station (SDZ), about 150 km from Beijing. Mean values (standarddeviation, S.D.) of scattering and absorption coefficients for the entireperiod are 174.6 Mm⁻¹ (189.1 Mm^-1) and 17.5 Mm⁻¹ (13.4 Mm^-1), respectively. These values are approximately one third of thereported values for scattering coefficients and one fifth of those forabsorption coefficients obtained in the Beijing urban area. The mean singlescattering albedo (SSA) for the entire period was estimated as 0.88 (0.05),which is about 0.07 higher than the values reported for the Beijing urbanarea, and also higher than the values (0.85) used in a reported climatesimulation for China and India. Both the absorption and scatteringcoefficients showed a seasonal cycle with the lowest values in winter, whilethe highest values occurred in summer for absorption coefficients and infall for scattering coefficients. The mean SSA values were lowest in springand highest in winter. The daily variations of aerosol absorption andscattering coefficients were strongly influenced by synoptic changesthroughout the observation period. A trajectory cluster analysis was appliedto discern the source characteristics of aerosol optical properties fordifferent air masses. The cluster-mean aerosol scattering coefficients,absorption coefficients and SSA were all high when the air masses moved fromSW and SE-E directions to the site and aerosols were influenced with heavypollution from the dense population centers and industrial areas. Thecluster-mean SSA for air masses coming from the polluted areas was not onlyhigher than those with trajectories from the "clean" directions, but alsohigher than the reported values for the regions with high pollutionemissions (such as the Beijing urban area). This fact might reflect thesubstantial secondary aerosol production during transport. Thecharacteristics of aerosol optical properties measured at this rural sitesuggest significant impacts of human activities on the regional aerosol.

[学科分类] 大气科学