Characteristics and direct radiative effect of mid-latitude continental aerosols: the ARM case

[摘要] A multi-year field measurement analysis of the characteristics and direct radiative effect ofaerosols at the Southern Great Plains (SGP) central facility of the Atmospheric RadiationMeasurement (ARM) Program is presented. Inter-annual mean and standard deviation ofsubmicrometer scattering fraction (at 550 nm) and Ångström exponent å(450 nm, 700 nm) at the mid-latitude continental site are indicative of the scattering dominance of fine modeaerosol particles, being 0.84±0.03 and 2.25±0.09, respectively. We attribute the diurnalvariation of submicron aerosol concentration to coagulation, photochemistry and the evolutionof the boundary layer. Precipitation does not seem to play a role in the observed afternoonmaximum in aerosol concentration. Submicron aerosol mass at the site peaks in the summer(12.1±6.7mgm^-3), with the summer value being twice that in the winter. Of the chemicallyanalyzed ionic components (which exclude carbonaceous aerosols), SO₄⁼and NH₄⁺ constitute the dominant species at the SGP seasonally, contributing23-30% and 9-12% of the submicron aerosol mass, respectively. Although a minor species, there is a notable rise inNO₃^- mass fraction in winter. We contrast the optical properties of dust and smoke haze. Thesingle scattering albedo w₀ shows the most remarkable distinction between the two aerosolconstituents. We also present aircraft measurements of vertical profiles of aerosol opticalproperties at the site. Annually, the lowest 1.2 km contributes 70% to the column total lightscattering coefficient. Column-averaged and surface annual mean values of hemisphericbackscatter fraction (at 550 nm), w₀(at 550 nm) and å (450 nm, 700 nm) agree to within 5% in 2001. Aerosols produce a netcooling (most pronounced in the spring) at the ARM site

[学科分类] 大气科学