Shortwave radiative forcing and efficiency of key aerosol types using AERONET data

Abstract

The shortwave radiative forcing (Δ<i>F</i>) and the radiative forcing efficiency (Δ<i>F</i><sup>eff</sup>) of natural and anthropogenic aerosols have been analyzed using estimates of radiation both at the top (TOA) and at the bottom of atmosphere (BOA) modeled based on AERONET aerosol retrievals. In this study we have considered six main types of atmospheric aerosols: desert mineral dust, biomass burning, urban-industrial, continental background, oceanic and free troposphere. The Δ<i>F</i> averages obtained vary from −148 ± 44 Wm<sup>−2</sup> (aerosol optical depth, AOD, at 0.55 μm, 0.85 ± 0.45) at the BOA for the mixture of desert mineral dust and biomass burning aerosols in Central Africa and −42 ± 22 Wm<sup>−2</sup> (AOD = 0.86 ± 0.51) at the TOA for the pure mineral dust also in this region up to −6 ± 3 Wm<sup>−2</sup> and −4 ± 2 Wm<sup>−2</sup> (AOD = 0.03 ± 0.02) at the BOA and the TOA, respectively, for free troposphere conditions. This last result may be taken as reference on a global scale. Furthermore, we observe that the more absorbing aerosols are overall more efficient at the BOA in contrast to at the TOA, where they backscatter less solar energy into the space. The analysis of the radiative balance at the TOA shows that, together with the amount of aerosols and their absorptive capacity, it is essential to consider the surface albedo of the region on which they are. Thus, we document that in regions with high surface reflectivity (deserts and snow conditions) atmospheric aerosols lead to a warming of the Earth-atmosphere system, contributing to the greenhouse gas effect

Ground-based remote sensing of aerosol climatology in China: Aerosol optical properties, direct radiative effect and its parameterization

“…Large standard deviation of ADRE BOA is related to variations of SZA, aerosol optical properties and surface albedo. ADRE BOA is close to the value derived in the Asiatic urbanindustrial region (À80 ± 52 W m À2 ) (Garcia et al, 2012). The regional ADRE BOA efficiencies derived from the linear analysis vary from À148 in R3 to À181 W m À2 in R4.…”

“…The regional ADRE BOA efficiencies derived from the linear analysis vary from À148 in R3 to À181 W m À2 in R4. The efficiency is slightly larger than those observed in the American regions (À135 W m À2 ) but close to those in the European urban-industrial region (À165 W m À2 ) (Garcia et al, 2012).…”

“…SSA uncertainty is estimated to be less than 0.03 for AOD at 440 nm > 0.4 . The inversion algorithm also calculates broadband solar radiation (Garcia et al, 2012). Solar radiation products under different aerosol environments at the BOA showed an excellent agreement with surface measurements (Garcia et al, 2008; 2010a,b).…”

“…The regional mean AOD and SSA are also presented in the figure. In order to compare results reported in the literature (Garcia et al, 2012), ADRE results have been limited at the solar zenith angle (SZA) of 60 ± 5 .…”

“…5 and 6. This fact is due to the increase multiple scattering effects and attenuation of the transmitted radiation as AOD increases (Garcia et al, 2012). Hence, a power law equation is used to describe this relationship:…”