Multiscale Modeling of Human Skin Oil-Induced Indoor Air Chemistry: Combining Kinetic Models and Molecular Dynamics

Abstract

We performed classical molecular dynamics simulations to quantify and understand the nonreactive, dermal uptake of volatile organic compounds formed during the ozonolysis of human skin oils. Our results include surface accommodation coefficients, partitioning constants, bulk diffusivities, and desorption lifetimes. These parameters were used to improve and to constrain the kinetic multilayer model of the surface and bulk chemistry of skin (KM-SUB-Skin). By comparing common outputs (bulk accommodation coefficients), we cross-validate the two approaches and, thus, increase the level of trust in their predictions relevant to indoor air chemistry.

Mass accommodation and gas–particle partitioning in secondary organic aerosols: dependence on diffusivity, volatility, particle-phase reactions, and penetration depth

“…Traditionally, SOA particles were assumed to be homogeneous and well-mixed quasi-liquid droplets (Pankow, 1994). As demonstrated by recent atmospheric measurements and laboratory experiments, they can adopt glassy solid or amorphous semi-solid phase states, challenging the traditional views of SOA properties, interactions, and effects Reid et al, 2018;Virtanen et al, 2010). Slow diffusion of water, oxidants, and organic molecules in viscous, semi-solid, or glassy particles may lead to kinetic limitations in heterogeneous and multiphase reactions (Alpert et al, 2019;Davies and Wilson, 2015;Kuwata and Martin, 2012;Zhang et al, 2018;Zhou et al, 2019).…”

Kinetic modeling of formation and evaporation of secondary organic aerosol from NO<sub>3</sub> oxidation of pure and mixed monoterpenes

“…Using these models, Shiraiwa et al (2013) and Zaveri et al (2018) were able to find evidence for diffusion limitation affecting SOA formation dynamics by inspection of the evolution of particle size distributions. Yli-Juuti et al (2017) and Tikkanen et al (2019) used an evaporation model based on KM-GAP to describe the interaction of volatility and viscosity during isothermal dilution as a function of different environmental conditions. However, to the best of our knowledge, no model has been presented that describes all aspects of gas-phase chemistry, particlephase chemistry, gas-particle partitioning, and bulk diffusion of SOA.…”

Mass Accommodation and Gas-Particle Partitioning in Secondary Organic Aerosols: Dependence on Diffusivity, Volatility, Particle-phase Reactions, and Penetration Depth

“…Figure 4b shows a wide range of other measurement-derived mass accommodation coefficients for various SOA and surrogate systems (data points/shaded areas) in comparison to generic values of aeff (lines) calculated for characteristic experimental conditions (w = 2.0´10 4 cm s -1 , rp = 1 g cm -3 , and rp = 100 nm, and Db = 10 -19 to 10 -5 cm 2 s -1 ). As indicated by molecular dynamics simulations and related studies, the surface accommodation coefficient (adsorption probability) for semi-volatile or low-volatile organic compounds on organic surfaces is likely close to unity, as = 1 (Julin et al, 2014;Von Domaros et al, 2020). Accordingly, low observational values of a can be attributed to the penetration-depth dependence of mass accommodation and plausibly explained by different scenarios/combinations/ratios of volatility and diffusivity, which can lead to a substantial decrease of aeff relative to as in semi-solid particles.…”

“…For a given surface accommodation coefficient of as = 1, which is likely a good approximation for SVOC on organic surfaces (Julin et al, 2014;Von Domaros et al, 2020), Figures 3a and 3b show how the effective mass accommodation coefficient aeff depends on volatility and bulk diffusivity as related to particle phase state and viscosity according to the Stokes-Einstein relation (Shiraiwa et al, 2011). In the liquid phase with high bulk diffusivity (Db > 10 -10 cm 2 s -1 ), aeff is essentially the same as as independent of volatility (aeff ≈ as ≈ 1).…”

“…Most model studies are using the Fuchs-Sutugin approximation of mass-transport kinetics at the gas-particle interface with a fixed mass accommodation coefficient that does not vary with particle phase state nor with the volatility and diffusivity of the investigated organic compounds. Molecular dynamics simulations (Julin et al, 2014;Von Domaros et al, 2020) and a recent SOA chamber study (Liu et al, 2019) suggest that the mass accommodation coefficients for semi-volatile organic molecules on organic substrates are close to unity. Measurement-derived mass accommodation coefficients reported from thermodenuder investigations of SOA volatility distributions, however, were one to three orders of magnitude lower (Kostenidou et al, 2018;Lee et al, 2010;Saleh et al, 2011).…”