Diffusion and reactivity in ultraviscous aerosol and the correlation with particle viscosity

Marshall, Frances H.; Miles, Rachael E. H.; Song, Young Chul; Ohm, Peter B.; Power, Rory M.; Reid, Jonathan P.; Dutcher, Cari S.

doi:10.1039/c5sc03223g

Cited by 111 publications

(130 citation statements)

References 54 publications

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“…However, unlike inorganic salts, saccharides have a steady water uptake mechanism, as observed in HTDMA hygroscopic data from the lack of a sharp deliquescent point ( Figure S4). 37 The lack of obvious crystalline structures at dry RH indicate that the saccharides retain some of their water content even in low humidity conditions, allowing us to probe a wide range of RH for these systems and therefore wider range of viscosity. 38 As an example, representative AFM 3D height image of glucose particle at ∼20% RH is shown ( Figure 6A); other saccharides display similar amorphous rounded morphology.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy

Lee

Estillore²,

Morris

et al. 2017

J. Phys. Chem. A

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Understanding the role of sea spray aerosol (SSA) on climate and the environment is of great interest due to their high number concentration throughout the Earth's atmosphere. Despite being of fundamental importance, direct surface tension measurements of SSA relevant sub-micrometer particles are rare, largely due to their extremely small volumes. Herein, atomic force microscopy (AFM) is used to directly measure the surface tension of individual sub-micrometer SSA particle mimics at ambient temperature and varying relative humidity (RH). Specifically, we probed both atmospherically relevant and fundamentally important model systems including electrolyte salts, dicarboxylic acids, and saccharides as single components and mixtures. Our results show that the single particle surface tension depends on RH or solute mole percentage and chemical composition. Moreover, for liquid droplets at and below 100 Pa s in viscosity, or at corresponding RH, we show good agreement between the AFM single particle and the bulk solution surface tension measurements at overlapping concentration ranges. Thus, direct surface tension measurements of individual particles using AFM is shown over a wide range of chemical systems as a function of RH, solute mole percentage, and viscosity than previously reported.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy

Lee

Estillore²,

Morris

et al. 2017

J. Phys. Chem. A

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“…The Stokes-Einstein relation is not expected to predict with high accuracy the diffusion rates of small gas molecules such as OH, O 3 , NO x , NH 3 , and H 2 O and may be inaccurate near the glass transition RH Shiraiwa et al, 2011). However, the Stokes-Einstein relationship should give reasonable estimations of diffusion rates for large organic molecules for conditions not close to the glass transition temperature of the matrix (Champion et al, 2000;Koop et al, 2011;Shiraiwa et al, 2011;Power et al, 2013;Marshall et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

et al. 2016

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Abstract. To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α-pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10 −1 to ∼ 6 × 10 6 Pa s from 30 to 90 % RH, and greater than ∼ 2 × 10 8 Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17 %. These viscosities correspond to Stokes-Einstein-equivalent diffusion coefficients for large organic molecules of ∼ 2 × 10 −15 cm 2 s −1 for 30 % RH, and lower than ∼ 3 × 10 −17 cm 2 s −1 for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1-5 h for 30 % RH, and higher than ∼ 100 h for RH ≤ 17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be wellmixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00-17:00 LT) during certain times of the year.

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“…Unfortunately, whilst viscosities of sucrose/water mixtures were measured over a large RH range, no viscosity data are available for our ternary system. Marshall et al (2016) highlighted that adding a third chemical compound to a binary matrix may significantly in- fluence its viscosity by comparing the viscosities of a water/sucrose/maleic acid system with that of aqueous sucrose at a given RH for higher maleic acid content. But given the generally low values of f PEG in this study, the viscosities of the ternary system should not significantly deviate from the viscosity of the binary aqueous sucrose at the same RH.…”

Section: Stokes-einstein Comparisonmentioning

confidence: 99%

“…Measured water diffusivities may exceed Stokes-Einstein predictions by several orders of magnitude (Power et al, 2013;Price et al, 2014). Several bulk and levitated aerosol particle techniques, based on isotopic tracers, fluorescence and mass transport measurements, have emerged to measure water diffusivity in highly viscous systems (Zobrist et al, 2011;Price et al, 2014;Lienhard et al, 2015;Davies and Wilson, 2016;Marshall et al, 2016). Few studies have addressed the diffusion of larger molecules (Champion et al, 1997;Price et al, 2016;Chenyakin et al, 2017) such as VOCs.…”

Section: Introductionmentioning

confidence: 99%

“…Few studies have addressed the diffusion of larger molecules (Champion et al, 1997;Price et al, 2016;Chenyakin et al, 2017) such as VOCs. Marshall et al (2016) studied the suppression of the evaporation of maleic acid in viscous sucrose aerosol and its dependence on RH, but stopped short of ascribing diffusivities, choosing instead to describe diffusion limitations qualitatively as apparent reduction in vapor pressure.…”

Section: Introductionmentioning

confidence: 99%

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Diffusivity measurements of volatile organics in levitated viscous aerosol particles

et al. 2017

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Abstract. Field measurements indicating that atmospheric secondary organic aerosol (SOA) particles can be present in a highly viscous, glassy state have spurred numerous studies addressing low diffusivities of water in glassy aerosols. The focus of these studies is on kinetic limitations of hygroscopic growth and the plasticizing effect of water. In contrast, much less is known about diffusion limitations of organic molecules and oxidants in viscous matrices. These may affect atmospheric chemistry and gas-particle partitioning of complex mixtures with constituents of different volatility. In this study, we quantify the diffusivity of a volatile organic in a viscous matrix. Evaporation of single particles generated from an aqueous solution of sucrose and small amounts of volatile tetraethylene glycol (PEG-4) is investigated in an electrodynamic balance at controlled relative humidity (RH) and temperature. The evaporative loss of PEG-4 as determined by Mie resonance spectroscopy is used in conjunction with a radially resolved diffusion model to retrieve translational diffusion coefficients of PEG-4. Comparison of the experimentally derived diffusivities with viscosity estimates for the ternary system reveals a breakdown of the Stokes-Einstein relationship, which has often been invoked to infer diffusivity from viscosity. The evaporation of PEG-4 shows pronounced RH and temperature dependencies and is severely depressed for RH 30 %, corresponding to diffusivities < 10 −14 cm 2 s −1 at temperatures < 15 • C. The temperature dependence is strong, suggesting a diffusion activation energy of about 300 kJ mol −1 . We conclude that atmospheric volatile organic compounds can be subject to severe diffusion limitations in viscous organic aerosol particles. This may enable an important long-range transport mechanism for organic material, including pollutant molecules such as polycyclic aromatic hydrocarbons (PAHs).

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Diffusion and reactivity in ultraviscous aerosol and the correlation with particle viscosity

Abstract: Direct comparison of diffusion coefficients and viscosities of ternary component single aerosol particles levitated using optical tweezers.

Cited by 111 publications

References 54 publications

Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy

Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

Diffusivity measurements of volatile organics in levitated viscous aerosol particles

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