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. 2017 Nov 28;114(48):12685-12690.
doi: 10.1073/pnas.1712273114. Epub 2017 Nov 13.

Mechanism of SOA formation determines magnitude of radiative effects

Jialei Zhu  1 , Joyce E Penner  2 , Guangxing Lin  3 , Cheng Zhou  1 , Li Xu  4 , Bingliang Zhuang  5
Affiliations

Mechanism of SOA formation determines magnitude of radiative effects

Jialei Zhu et al. Proc Natl Acad Sci U S A. .

Abstract

Secondary organic aerosol (SOA) nearly always exists as an internal mixture, and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing state based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66% of SOA is internally mixed with sulfate, while 34% is internally mixed with primary soot. Compared with using an external mixture, the direct effect of SOA is decreased due to the decrease in total aerosol surface area and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced, and this is responsible for a large decrease in the cloud albedo effect. Internal mixing decreases the radiative effect of SOA by a factor of >4 compared with treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of -0.05 W m-2 When the combined effects of changes in climate, anthropogenic emissions, and land use are included, the SOA forcing is -0.07 W m-2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing.

Keywords: SOA; future climate; mixing state; radiative effects.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Percentage of SOA internally mixed with sulfate in the nucleation (A), Aitken (B), and accumulation (C) modes, fSoot (D), bSoot (E), and other aerosols (dust and sea salt) (F) in the IM scheme.
Fig. 2.
Fig. 2.
Present-day DRE and AIE due to SOA in EM (A and B), IM (C and D), and IM_OC (E and F) (W m−2). The global average radiative effect of SOA is given in each figure label.
Fig. 3.
Fig. 3.
Spatial distribution of DRF and first IRF in the FUCLI scheme due to changes in climate and CO2 (A and B) and in the FUALL scheme due to changes in climate, all anthropogenic emissions, and land use (C and D). The global average RF of SOA is given in each figure label.
See this image and copyright information in PMC

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