Mechanism of SOA formation determines magnitude of radiative effects

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 radiati...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2017-11, Vol.114 (48), p.12685-12690
Main Authors: Zhu, Jialei, Penner, Joyce E., Lin, Guangxing, Zhou, Cheng, Xu, Li, Zhuang, Bingliang
Format: Article
Language:English
Subjects:
Aerosols
Albedo
Anthropogenic factors
Atmospheric aerosols
Carbon dioxide
Climate change
Climate effects
Emissions control
ENVIRONMENTAL SCIENCES
Human influences
Land use
Physical Sciences
Radiative forcing
Soot
Sulfates
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Summary: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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1712273114