Modeling the Size Distribution and Chemical Composition of Secondary Organic Aerosols during the Reactive Uptake of Isoprene-Derived Epoxydiols under Low-Humidity Condition

Abstract

Reactive uptake of isoprene epoxydiols (IEPOX), which are isoprene oxidation products, onto acidic sulfate aerosols is recognized to be an important mechanism for the formation of isoprene-derived secondary organic aerosol (SOA). While a mechanistic understanding of IEPOX-SOA formation exists, several processes affecting their formation remain uncertain. Evaluating mechanistic IEPOX-SOA models with controlled laboratory experiments under longer atmospherically relevant time scales is critical. Here, we implement our latest understanding of IEPOX-SOA formation within a box model to simulate the measured reactive uptake of IEPOX on polydisperse ammonium bisulfate seed aerosols within an environmental Teflon chamber. The model is evaluated with single-particle measurements of size distribution, volume, density, and composition of aerosols due to IEPOX-SOA formation at time scales of hours. We find that the model can simulate the growth of particles due to IEPOX multiphase chemistry, as reflected in increases of the mean particle size and volume concentrations, and a shift of the number size distribution to larger sizes. The model also predicts the observed evolution of particle number mean diameter and total volume concentrations at the end of the experiment. We show that in addition to the self-limiting effects of IEPOX-SOA coatings, the mass accommodation coefficient of IEPOX and accounting for the molar balance between inorganic and organic sulfate are important parameters governing the modeling of the IEPOX-SOA formation. Thus, models which do not account for the molar sulfate balance and/or diffusion limitations within IEPOX-SOA coatings are likely to predict IEPOX-SOA formation too high.

Observationally Constrained Modeling of the Reactive Uptake of Isoprene-Derived Epoxydiols under Elevated Relative Humidity and Varying Acidity of Seed Aerosol Conditions

“…During the calculation, the H + activity ( a H + ) represents the molar concentration of H + , which is adjusted by multiplying the H + activity coefficient based on E-AIM model. , Only the aerosol water content associated with the inorganic phase (M of aerosols) is used as nucleophile H 2 O. k i , j is third-order reaction rate constants (M 2 s –1 ). Their values are derived from previous kinetic studies ,, and summarized in Table (base case), which were first compiled in Budisulistiorini et al’s work and applied in most current modeling studies. ,,, In this study, these reaction rate constants were reassessed and constrained by the chamber-measured particle size evolution and SOA product composition (see Table , LowRxn case). The two major SOA products formed through the aqueous-phase reactions are tetrols and IEPOX-organosulfates (i.e., methyltetrol sulfates or OSs) .…”

Tight Coupling of Surface and In-Plant Biochemistry and Convection Governs Key Fine Particulate Components over the Amazon Rainforest

“…This mechanism was also recently evaluated against laboratory single-particle measurements of IEPOX-SOA formation in a Teflon chamber at timescales of ∼hours under low-relative humidity (RH) conditions. 22 Figure 2 schematically illustrates simulated multiphase chemistry processes occurring during the reactive uptake of IEPOX gas on aqueous inorganic aerosols, which were included in WRF-Chem to represent chemistry in the gas phase, aqueous aerosols, and clouds.…”

“…The detailed mechanisms and equations governing the multiphase reactive uptake of IEPOX and the role of viscous SOA coatings limiting IEPOX-SOA formation, which we implemented in WRF-Chem, are described in the Supporting Information, IEPOX reactive uptake , and Tables S1 and S2. This mechanism was also recently evaluated against laboratory single-particle measurements of IEPOX-SOA formation in a Teflon chamber at timescales of ∼hours under low-relative humidity (RH) conditions Figure schematically illustrates simulated multiphase chemistry processes occurring during the reactive uptake of IEPOX gas on aqueous inorganic aerosols, which were included in WRF-Chem to represent chemistry in the gas phase, aqueous aerosols, and clouds.…”

Predicting glass transition temperature and melting point of organic compounds via machine learning and molecular embeddings

“…Their results suggest functionalization is a crucial predictive parameter for molecular T g . These parameterizations are simple, practical, and versatile prediction methods, which have been applied to estimate SOA viscosity for high-resolution mass spectrometry 8,[17][18][19] and also implemented into thermodynamic, 20,21 gas-phase chemistry models 9 and chemical transport models. 5,22,23 These parameterizations, however, have relatively larger uncertainties ($25 K) and they do not account for molecular structure and functional groups presence.…”