Mechanism of SOA formation determines magnitude of radiative effects

Jialei Zhu; Joyce E Penner; Guangxing Lin; Cheng Zhou; Li Xu; Bingliang Zhuang

doi:10.1073/pnas.1712273114

Mechanism of SOA formation determines magnitude of radiative effects

Proc Natl Acad Sci U S A. 2017 Nov 28;114(48):12685-12690. doi: 10.1073/pnas.1712273114. Epub 2017 Nov 13.

Authors

Jialei Zhu¹, Joyce E Penner², Guangxing Lin³, Cheng Zhou¹, Li Xu⁴, Bingliang Zhuang⁵

Affiliations

¹ Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109.
² Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109; penner@umich.edu.
³ Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA 99354.
⁴ Department of Earth System Science, University of California, Irvine, CA 92697.
⁵ School of Atmospheric Sciences, Nanjing University, Nanjing, Jiangsu Province 210023, China.

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.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.