Effect of Bulk Composition on the Heterogeneous Oxidation of Semi-Solid Atmospheric Aerosols

Fan, Hanyu; Goulay, Fabien

doi:10.3390/atmos10120791

Cited by 3 publications

(6 citation statements)

References 60 publications

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“…Since OH radicals are highly reactive, the reactive uptake of OH radicals by OA species and subsequent effects on the particles’ optical properties, hygroscopicity, and cloud condensation nucleus (CCN) activity have been extensively studied. ,,− Several experimental studies have examined the effect of particle viscosity on the OH reactive uptake, where particle viscosity is modulated by RH or organic composition. ,,,− For example, Slade and Knopf observed that γ (the fraction of colliding OH radicals that lead to reaction) of OH and levoglucosan (LEV) increases by a factor of 3 as RH increases from 0 to 40%, which is attributed to enhanced diffusivity as LEV gradually deliquesces with increasing RH . Davies and Wilson also reported that increasing RH from 20 to 50% lowers the viscosity of citric acid (CA) from 2 to 0.2 Pa s, thereby enhancing the OH reactivity by about a factor of 3.…”

Section: Introductionmentioning

confidence: 99%

Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions

Knopf

2021

Environ. Sci. Technol.

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Organic aerosol (OA) is ubiquitous in the atmosphere and, during transport, can experience chemical transformation with consequences for air quality and climate. Prediction of the chemical evolution of OA depends on its reactivity with atmospheric oxidants such as the OH radical. OA particles undergo amorphous phase transitions from liquid to solid (glassy) states in response to temperature changes, which, in turn, will impact its reactivity toward OH oxidation. To improve the predictability of OA reactivity toward OH oxidation, the reactive uptake coefficients (γ) of OH radicals reacting with triacontane and squalane serving as amorphous OA surrogates were measured at temperatures from 213−293 K. γ increases strongest with temperature when the organic species is in the liquid phase, compared to when being in the semisolid or solid phase. The resistor model is applied, accounting for the amorphous phase state changes using the organic species' glass transition temperature and fragility, to evaluate the physicochemical parameters of the temperature dependent OH uptake process. This allows for the derivation of a semiempirical formula, applicable to models, to predict the degree of oxidation and chemical lifetime of the condensed-phase organic species for typical tropospheric temperature and humidity when OA particle viscosity is known.

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Section: Introductionmentioning

confidence: 99%

Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions

Knopf

2021

Environ. Sci. Technol.

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“…When diffusion is not the rate limiting step, thermodynamic equilibrium is reached and the composition of the air−water interface is governed by the surface−bulk partitioning properties of the solutes. 13,32,33 Surfactants with long alkyl chains have been detected in atmospheric aerosols and are known to accumulate at the surface. 3,34,35 Smaller, more hydrophilic molecules and ions also display surface−bulk partitioning leading to a solute concentration gradient close to the air−water interface.…”

Section: Introductionmentioning

confidence: 99%

“…In multicomponent particles, even though the solutes are dilute enough to neglect intermolecular interactions, concentration gradients near the surface lead to solute reactive uptake coefficients that are different from those observed in a single component particle. 32 A better understanding of the effect of composition on the chemical fate of aerosols under oxidative conditions therefore requires a systematic investigation of the effect of the organic functional groups on heterogeneous reactivity. Amides and saccharides are good archetypal molecules for investigating such effects as they display a very wide range of partitioning properties.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of several organic compounds in aqueous aerosols results in the formation of coexisting liquid phases within the same aerosol. − In the case of water-miscible organic solutes, the core of the liquid particle, hereafter referred to as the particle bulk, acts as an infinite chemical reservoir for the outer phase. When diffusion is not the rate limiting step, thermodynamic equilibrium is reached and the composition of the air–water interface is governed by the surface–bulk partitioning properties of the solutes. ,, Surfactants with long alkyl chains have been detected in atmospheric aerosols and are known to accumulate at the surface. ,, Smaller, more hydrophilic molecules and ions also display surface–bulk partitioning leading to a solute concentration gradient close to the air–water interface. ,, Surface active molecule moves to the interface, decreasing the surface tension, , while surface inactive molecules are excluded from it, leading to an increase of the surface tension . The changes in surface tension in atmospheric aerosols affect natural processes, especially cloud nucleation. , A molecular-level understanding of the properties of the interface is required to fully understand the fundamental processes governing the chemical evolution of aerosols.…”

Section: Introductionmentioning

confidence: 99%

“…Atmospheric aerosols contain a wide range of solutes with different organic functional groups. In multicomponent particles, even though the solutes are dilute enough to neglect intermolecular interactions, concentration gradients near the surface lead to solute reactive uptake coefficients that are different from those observed in a single component particle . A better understanding of the effect of composition on the chemical fate of aerosols under oxidative conditions therefore requires a systematic investigation of the effect of the organic functional groups on heterogeneous reactivity.…”

Section: Introductionmentioning

confidence: 99%

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A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols

Masaya

Goulay

2023

J. Phys. Chem. A

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The surface−bulk partitioning of small saccharide and amide molecules in aqueous droplets was investigated using molecular dynamics. The air−particle interface was modeled using a 80 Å cubic water box containing a series of organic molecules and surrounded by gaseous OH radicals. The properties of the organic solutes within the interface and the water bulk were examined at a molecular level using density profiles and radial pair distribution functions. Molecules containing only polar functional groups such as urea and glucose are found predominantly in the water bulk, forming an exclusion layer near the water surface. Substitution of a single polar group by an alkyl group in sugars and amides leads to the migration of the molecule toward the interface. Within the first 2 nm from the water surface, surface-active solutes lose their rotational freedom and adopt a preferred orientation with the alkyl group pointing toward the surface. The different packing within the interface leads to different solvation shell structures and enhanced interaction between the organic molecules and absorbed OH radicals. The simulations provide quantitative information about the dimension, composition, and organization of the air−water interface as well as about the nonreactive interaction of the OH radicals with the organic solutes. It suggests that increased concentrations, preferred orientations, and decreased solvation near the air−water surface may lead to differences in reactivities between surface-active and surface-inactive molecules. The results are important to explain how heterogeneous oxidation mechanisms and kinetics within interfaces may differ from those of the bulk.

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Modeling the Impact of the Organic Aerosol Phase State on Multiphase OH Reactive Uptake Kinetics and the Resultant Heterogeneous Oxidation Timescale of Organic Aerosol in the Amazon Rainforest

Rasool

Shrivastava

Liu

et al. 2023

ACS Earth Space Chem.

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Accurate predictions of chemical lifetime, i.e., oxidation timescale and change in the mass of organic aerosols (OAs) in atmospheric models, are critical to quantify the impacts of OA on aerosol–cloud interactions, radiative forcing, and air quality. The heterogeneous oxidation of OA by hydroxyl (OH) radicals is a key process governing OA mass changes during their oxidation. Recently, laboratory observations of the OH uptake coefficient (γOH) and heterogeneous reaction rate (k het,OH) for different OA systems with varying phase states have been combined to develop a new parameterization of γOH and k het,OH as a function of the OA phase state, i.e., viscosity (ηOA). In this work, we use a recently published viscosity prediction framework to analyze the new γOH and k het,OH parameterization with a box model. Subsequently, we implement this box model to predict γOH and k het,OH over the Amazon rainforest in the dry-to-wet transition season with both significant biomass burning and biogenic influences. Relevant parameters within our box model are specified based on detailed regional model simulations over the Amazon using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). ηOA is predicted as a function of species volatility, OA composition (including water uptake) along with ambient relative humidity (RH), and temperature. Based on ambient conditions simulated by WRF-Chem over the entire atmospheric column, we use the box model to predict the upper bounds of the heterogeneous oxidation timescale of OA. Based on previous laboratory measurements, we assume that this heterogeneous OH oxidation causes fragmentation (carbon loss) of OA, followed by the evaporation of the fragmented molecules that results in the exponential decay of OA. We predict that the oxidation timescale of OA is ∼1 month near the Earth’s surface in the pristine Amazonian background because of low OH concentrations. But OA is oxidized more rapidly within urban and wildfire plumes near the Earth’s surface with an order of magnitude higher OH concentrations compared to the pristine background, causing the simulated oxidation timescale of OA to be much shorter, ∼3–4 days. At 3–5 km altitudes where biomass burning OA is predicted to be semisolid, the heterogeneous oxidation timescale is estimated as ∼6 days to 3 weeks and decreases with increasing OH concentrations within plumes. We show that the simulated mass loss of OA is strongly size-dependent, where smaller particles oxidize more rapidly compared to larger particles due to their greater per-particle surface area-to-volume ratio. Increasing urbanization and deforestation in the Amazon in the future might increase OH concentrations in the background Amazon, causing faster oxidation of OA. At higher altitudes above liquid clouds, especially in the upper troposphere where temperatures approach ∼250 K, future measurements are needed to reduce the uncertainties related to the mass loss of OA at colder temperatures and low relative humidity conditions due to its heterogeneous OH ...

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Effect of Bulk Composition on the Heterogeneous Oxidation of Semi-Solid Atmospheric Aerosols

Cited by 3 publications

References 60 publications

Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions

Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions

A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols

Modeling the Impact of the Organic Aerosol Phase State on Multiphase OH Reactive Uptake Kinetics and the Resultant Heterogeneous Oxidation Timescale of Organic Aerosol in the Amazon Rainforest

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