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Title: A simplified parameterization of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) for global chemistry and climate models: a case study with GEOS-Chem v11-02-rc

Abstract. Secondary organic aerosol derived from isopreneepoxydiols (IEPOX-SOA) is thought to contribute the dominant fraction oftotal isoprene SOA, but the current volatility-based lumped SOAparameterizations are not appropriate to represent the reactive uptake ofIEPOX onto acidified aerosols. A full explicit modeling of this chemistryis however computationally expensive owing to the many species and reactionstracked, which makes it difficult to include it in chemistry–climate modelsfor long-term studies. Here we present three simplified parameterizations(version 1.0) for IEPOX-SOA simulation, based on an approximateanalytical/fitting solution of the IEPOX-SOA yield and formation timescale.The yield and timescale can then be directly calculated using the globalmodel fields of oxidants, NO, aerosol pH and other key properties, and drydeposition rates. The advantage of the proposed parameterizations is thatthey do not require the simulation of the intermediates while retaining thekey physicochemical dependencies. We have implemented the newparameterizations into the GEOS-Chem v11-02-rc chemical transport model,which has two empirical treatments for isoprene SOA (the volatility-basis-set, VBS, approach and a fixed 3 % yield parameterization), and comparedall of them to the case with detailed fully explicit chemistry. The bestparameterization (PAR3) captures the global tropospheric burden of IEPOX-SOAand its spatiotemporal distribution (R2=0.94) vs. thosesimulated by the full chemistry, while being more computationally efficient(∼5 times faster), and accurately captures the response tochanges in NOx and SO2 emissions. On the other hand, the constant3 % yield that is now the default in GEOS-Chem deviates strongly (R2=0.66), as does the VBS (R2=0.47, 49 % underestimation), withneither parameterization capturing the response to emission changes. Withthe advent of new mass spectrometry instrumentation, many detailed SOAmechanisms are being developed, which will challenge global and especiallyclimate models with their computational cost. The methods developed in thisstudy can be applied to other SOA pathways, which can allow includingaccurate SOA simulations in climate and global modeling studies in thefuture.

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Author(s) / Creator(s):
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Date Published:
Journal Name:
Geoscientific Model Development
Page Range / eLocation ID:
2983 to 3000
Medium: X
Sponsoring Org:
National Science Foundation
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