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Wallace BJ, Mongeau ML, Zuend A, Preston TC. Impact of pH on Gas-Particle Partitioning of Semi-Volatile Organics in Multicomponent Aerosol. Environ Sci Technol 2023; 57:16974-16988. [PMID: 37885068 DOI: 10.1021/acs.est.3c02894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2023]
Abstract
The partitioning of semivolatile organic compounds (SVOCs) between the condensed and gas phases can have significant implications for the properties of aerosol particles. In addition to affecting size and composition, this partitioning can alter radiative properties and impact cloud activation processes. We present measurements and model predictions on how activity and pH influence the evaporation of SVOCs from particles to the gas phase, specifically investigating aqueous inorganic particles containing dicarboxylic acids (DCAs). The aerosols are studied at the single-particle level by using optical trapping and cavity-enhanced Raman spectroscopy. Optical resonances in the spectra enable precise size tracking, while vibrational bands allow real-time monitoring of pH. Results are compared to a Maxwell-type model that accounts for volatile and nonvolatile solutes in aqueous droplets that are held at a constant relative humidity. The aerosol inorganic-organic mixture functional group activity coefficients thermodynamic model and Debye-Hückel theory are both used to calculate the activities of the species present in the droplet. For DCAs, we find that the evaporation rate is highly sensitive to the particle pH. For acidity changes of approximately 1.5 pH units, we observe a shift from a volatile system to one that is completely nonvolatile. We also observe that the pH itself is not constant during evaporation; it increases as DCAs evaporate, slowing the rate of evaporation until it eventually ceases. Whether a DCA evaporates or remains a stable component of the droplet is determined by the difference between the lowest pKa of the DCA and the pH of the droplet.
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Affiliation(s)
- Brandon J Wallace
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada
| | - Michel Laforest Mongeau
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada
| | - Andreas Zuend
- Department of Atmospheric and Oceanic Sciences, McGill University, 805 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B9
| | - Thomas C Preston
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada
- Department of Atmospheric and Oceanic Sciences, McGill University, 805 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B9
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2
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Rafferty A, Vennes B, Bain A, Preston TC. Optical trapping and light scattering in atmospheric aerosol science. Phys Chem Chem Phys 2023; 25:7066-7089. [PMID: 36852581 DOI: 10.1039/d2cp05301b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
Aerosol particles are ubiquitous in the atmosphere, and currently contribute a large uncertainty to climate models. Part of the endeavour to reduce this uncertainty takes the form of improving our understanding of aerosol at the microphysical level, thus enabling chemical and physical processes to be more accurately represented in larger scale models. In addition to modeling efforts, there is a need to develop new instruments and methodologies to interrogate the physicochemical properties of aerosol. This perspective presents the development, theory, and application of optical trapping, a powerful tool for single particle investigations of aerosol. After providing an overview of the role of aerosol in Earth's atmosphere and the microphysics of these particles, we present a brief history of optical trapping and a more detailed look at its application to aerosol particles. We also compare optical trapping to other single particle techniques. Understanding the interaction of light with single particles is essential for interpreting experimental measurements. In the final part of this perspective, we provide the relevant formalism for understanding both elastic and inelastic light scattering for single particles. The developments discussed here go beyond Mie theory and include both how particle and beam shape affect spectra. Throughout the entirety of this work, we highlight numerous references and examples, mostly from the last decade, of the application of optical trapping to systems that are relevant to the atmospheric aerosol.
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Affiliation(s)
| | - Benjamin Vennes
- Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada.
| | - Alison Bain
- School of Chemistry, University of Bristol, Bristol, UK
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada. .,Department of Chemistry, McGill University, Montreal, Quebec, Canada
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3
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Price CL, Preston TC, Davies JF. Hygroscopic Growth, Phase Morphology, and Optical Properties of Model Aqueous Brown Carbon Aerosol. Environ Sci Technol 2022; 56:3941-3951. [PMID: 35312301 DOI: 10.1021/acs.est.1c07356] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Brown carbon aerosol in the atmosphere contain light-absorbing chromophores that influence the optical scattering properties of the particles. These chromophores may be hydrophobic, such as PAHs, or water soluble, such as nitroaromatics, imidazoles, and other conjugated oxygen-rich molecules. Water-soluble chromophores are expected to exist in aqueous solution in the presence of sufficient water and will exhibit physical properties (e.g., size, refractive index, and phase morphology) that depend on the environmental relative humidity (RH). In this work, we characterize the RH-dependent properties of 4-nitrocatechol (4-NC) and its mixtures with ammonium sulfate, utilizing a single-particle levitation platform coupled with Mie resonance spectroscopy to probe the size, real part of the complex refractive index (RI), and phase morphology of individual micron-sized particles. We measure the hygroscopic growth properties of pure 4-NC and apply mixing rules to characterize the growth of mixtures with ammonium sulfate. We report the RI at 589 nm for these samples as a function of RH and explore the wavelength dependence of the RI at non-absorbing wavelengths. The real part of the RI at 589 nm was found to vary in the range 1.54-1.59 for pure 4-NC from 92.5 to 75% RH, with an estimated pure component RI of 1.70. The real part of the RI was also measured for mixtures of AS and 4-NC and ranged from 1.39 to 1.51 depending on the component ratio and RH. We went on to characterize phase transitions in mixed particles, identifying the onset RH of liquid-liquid phase separation (LLPS) and efflorescence transitions. Mixtures showed LLPS in the range of 85-76% RH depending on the molar ratio, while efflorescence typically fell between 22 and 42% RH. Finally, we characterized the imaginary part of the complex RI using an effective oscillator model to capture the wavelength-dependent absorption properties of the system.
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Affiliation(s)
- Chelsea L Price
- Department of Chemistry, University of California Riverside, Riverside, California 92521, United States
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, Quebec H3A 0B9, Canada
| | - James F Davies
- Department of Chemistry, University of California Riverside, Riverside, California 92521, United States
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Abstract
Slow condensed phase diffusion in organic aerosol particles can impede many chemical and physical processes associated with atmospheric aerosol (e.g., gas-particle equilibrium partitioning). The characteristic times associated with these high viscosity particles are typically modelled using a concentration-dependent diffusivity within a purely Fickian framework. In that model, the medium in which diffusion is taking place is treated as being inviscid as far as mass transport is concerned. In this report, we investigate the validity of assuming that the viscosity is equal to zero by using a transport model that includes viscous pressure gradients. It is found that the effect of viscosity is negligible for particles with radii that are larger than 100 nm, but below that radius, it can delay water uptake and loss by orders of magnitude for physically realistic viscosities. However, if the Stokes–Einstein relation is obeyed, then viscosity can be ignored, even for nanosized particles. In addition to numerical calculations, a dimensionless Deborah number is defined that indicates the significance of Fickian diffusion compared with the rheological response during water transport.
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Affiliation(s)
- Thomas C. Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC H3A 0B9, Canada
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC H3A 0B9, Canada
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5
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Abstract
An optical trapping cell that is capable of suspending particles using two counter-propagating beams in a temperature-controlled environment is reported here. With this dual-beam optical trap, we are able to hold single micron-sized droplets at temperatures down to 253 K (-20 °C) for hours at a time and in metastable (supercooled) states. As particles are trapped at the shared focal points of two intense beams, strong cavity-enhanced Raman scattering (CERS) is observed and allows for high precision measurements of physical properties. Here, the evaporation of highly oxygenated organic systems was monitored using CERS and was used to determine temperature-dependent vapor pressures and enthalpies of vaporization. The wavelength- and temperature-dependent optical properties were also simultaneously retrieved using CERS.
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Affiliation(s)
- Alexander Logozzo
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B9
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B9
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Abstract
A growing body of research suggests the presence and long-range transport of microplastics in the atmosphere. However, the interactions between these microplastics and atmospheric aerosol are poorly understood. Environmental microplastics vary in color, morphology, and chemical composition and become oxidized over time by UV, mechanical, and biological action. Once introduced to the atmosphere, these microplastics will likely become mixed with atmospheric aerosol. Determining how microplastics interact with aerosol particles and how they may alter aerosol physical properties, including water uptake and loss, is necessary to understand the impact of these microplastics on our environment. Herein, we investigate the effect of microplastics on the water activity of bulk water and ammonium sulfate solutions. We compare a variety of plastic compositions and microplastic morphologies including plastics that have been aged by UV irradiation and mechanical forces in the lab. In addition, we investigate the water uptake and loss in microplastic samples through dynamic vapor sorption. We find an increase in total water sorption for UV-aged plastics compared to pristine plastics. Finally, we investigate the effect of fractional surface coverage on the equilibration time scale.
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Affiliation(s)
- Alison Bain
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 0B9
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 0B9
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Abstract
Condensed phase mass transport in single aerosol particles is investigated using a linear quadrupole electrodynamic balance (LQ-EDB) and the Maxwell–Stefan (MS) framework.
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Affiliation(s)
- Brandon J. Wallace
- Department of Atmospheric and Oceanic Sciences
- Department of Chemistry
- McGill University
- Montreal
- Canada
| | - Chelsea L. Price
- Department of Chemistry
- University of California Riverside
- Riverside
- USA
| | - James F. Davies
- Department of Chemistry
- University of California Riverside
- Riverside
- USA
| | - Thomas C. Preston
- Department of Atmospheric and Oceanic Sciences
- Department of Chemistry
- McGill University
- Montreal
- Canada
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8
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Price CL, Bain A, Wallace BJ, Preston TC, Davies JF. Simultaneous Retrieval of the Size and Refractive Index of Suspended Droplets in a Linear Quadrupole Electrodynamic Balance. J Phys Chem A 2020; 124:1811-1820. [PMID: 32013433 DOI: 10.1021/acs.jpca.9b10748] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Single-particle trapping is an effective strategy to explore the physical and optical properties of aerosol with high precision. Laser-based methods are commonly used to probe the size, optical properties, and composition of nonlight-absorbing droplets in optical and electrodynamic traps. However, these methods cannot be applied to droplets containing photoactive chromophores, and thus, single-particle methods have been restricted to only a subset of atmospherically relevant particle compositions. In this work, we explore the application of a broadband light scattering approach, Mie resonance spectroscopy, to simultaneously probe the size and the refractive index (RI) of droplets in a linear quadrupole electrodynamic balance. We examine the evaporation of poly(ethylene glycol)s and compare the calculated vapor pressures with literature values to benchmark the size accuracy without prior constraint on the RI. We then explore the hygroscopic growth and deliquescence of sodium chloride droplets, measuring RI at the deliquescence relative humidity and demonstrating agreement to literature values. These data allow the wavelength dependence of the RI of aqueous NaCl to be determined using a first-order Cauchy equation, and we effectively reproduce literature data from multiple techniques. We finally discuss measurements from a light-absorbing aqueous droplet containing humic acid and interpret the spectra via the imaginary component of the RI. The approach described here allows the radius of nonabsorbing droplets to be determined within 0.1%, the refractive index within 0.2%, and the first-order term in the Cauchy dispersion equation within ∼5%.
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Affiliation(s)
- Chelsea L Price
- Department of Chemistry, University of California Riverside, Riverside, California 92420, United States
| | - Alison Bain
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, Montreal, Quebec H3A 0G4, Canada
| | - Brandon J Wallace
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, Montreal, Quebec H3A 0G4, Canada
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, Montreal, Quebec H3A 0G4, Canada
| | - James F Davies
- Department of Chemistry, University of California Riverside, Riverside, California 92420, United States
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9
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Abstract
A model for calculating the wavelength-dependent refractive index of multicomponent mixtures is presented and applied to aqueous systems in the atmosphere and oceans.
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Affiliation(s)
- Alison Bain
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
- McGill University
- Montreal
- Canada
| | - Thomas C. Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
- McGill University
- Montreal
- Canada
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10
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Vennes B, Preston TC. Calculating and fitting morphology-dependent resonances of a spherical particle with a concentric spherical shell. J Opt Soc Am A Opt Image Sci Vis 2019; 36:2089-2103. [PMID: 31873383 DOI: 10.1364/josaa.36.002089] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 10/22/2019] [Indexed: 06/10/2023]
Abstract
Determining the size and composition of core-shell particles using morphology-dependent resonances (MDRs) is a computationally intensive problem due to the large parameter space that needs to be searched during the fitting process. Very often, it is not even practical to consider a reasonable range of physical parameters due to time constraints, leading to restrictive assumptions concerning the system being studied. The lengthy computational time is so limiting that there has, to date, to the best of our knowledge, been no comprehensive study of fitting measured MDRs for core-shell particles. In this work, we address the issue of fitting speed by developing an algorithm that (i) reduces the multi-dimensional grid search to a one-dimensional search using a least squares method and (ii) implements a new method for calculating MDRs that is much faster than previous methods. With the program presented here, we analyze the best-fits for core-shell MDRs across a large range of physically relevant scenarios using noise levels typical for conventional spectroscopic experiments. For many cases, it has been found that excellent fits can be quickly determined. However, there are also some surprising situations where accurate best-fits are not possible (e.g., if only one mode order is present in the measured MDR set).
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Abstract
An accurate understanding of the equilibration timescale of organic aerosol particles with surrounding water vapor is difficult because of the strong concentration-dependent diffusivities that are present in these systems. We examine this problem along with the closely related problem of the time-dependent radius of a binary aerosol particle during the uptake or loss of water. The governing equations and boundary conditions are discussed and a boundary value problem is formulated and solved. The resulting expressions are applied to water uptake and loss in two systems of atmospheric importance: aqueous-inorganic particles and high-viscosity organic particles. Accuracy is evaluated through a comparison with numerical solutions. For particles whose diffusivity has a strong dependence on water concentration and whose viscosity remains above 1 Pa·s during water uptake or loss, the expression for the characteristic equilibration time is found to be in excellent agreement with numerical results. Moreover, it provides physical insights into mass transport processes.
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Affiliation(s)
- Brandon J Wallace
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry , McGill University , 805 Sherbrooke Street West , Montreal , H3A 0B9 Québec , Canada
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry , McGill University , 805 Sherbrooke Street West , Montreal , H3A 0B9 Québec , Canada
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12
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Lew LJN, Ting MV, Preston TC. Determining the size and refractive index of homogeneous spherical aerosol particles using Mie resonance spectroscopy. Appl Opt 2018; 57:4601-4609. [PMID: 29877369 DOI: 10.1364/ao.57.004601] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/01/2018] [Indexed: 06/08/2023]
Abstract
Methods for determining the size and refractive index of single, homogeneous, micrometer-sized aerosol particles using Mie resonance spectroscopy are studied using measurements from optically trapped particles and light-scattering calculations based on Mie theory. We consider both single-particle broadband light scattering and cavity-enhanced Raman scattering (CERS) and demonstrate that, when resonances observed in either type of spectroscopy are fitted using Mie theory, the accuracy of the best fits are similar. However, broadband measurements can yield more resonances than CERS, thus reducing the uncertainty in the retrieved parameters of best fit and increasing the range of particles that can be characterized. Resonance fitting methods are also compared to methods that fit the entire Mie scattering spectrum. Through calculations, it is shown that measured scattering spectra are sensitive to small changes in how light is collected, while Mie resonance positions are much less sensitive. This means that additional parameters are required to accurately fit entire light-scattering spectra using Mie theory, but these parameters are not needed to accurately determine Mie resonance positions.
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13
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Rafferty A, Preston TC. Measuring the size and complex refractive index of an aqueous aerosol particle using electromagnetic heating and cavity-enhanced Raman scattering. Phys Chem Chem Phys 2018; 20:17038-17047. [DOI: 10.1039/c8cp02966k] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We describe a dual-beam optical trap that can simultaneously determine the complex refractive index and the radius of weakly absorbing aerosol particles.
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Affiliation(s)
- Aidan Rafferty
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
- McGill University
- Montreal
- Canada
| | - Thomas C. Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
- McGill University
- Montreal
- Canada
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14
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Moridnejad A, Preston TC, Krieger UK. Tracking Water Sorption in Glassy Aerosol Particles using Morphology-Dependent Resonances. J Phys Chem A 2017; 121:8176-8184. [DOI: 10.1021/acs.jpca.7b06774] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ali Moridnejad
- Department
of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 0B9
| | - Thomas C. Preston
- Department
of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 0B9
| | - Ulrich K. Krieger
- Institute
for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
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15
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Preston TC, Davies JF, Wilson KR. The frequency-dependent response of single aerosol particles to vapour phase oscillations and its application in measuring diffusion coefficients. Phys Chem Chem Phys 2017; 19:3922-3931. [PMID: 28106191 DOI: 10.1039/c6cp07711k] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new method for measuring diffusion in the condensed phase of single aerosol particles is proposed and demonstrated. The technique is based on the frequency-dependent response of a binary particle to oscillations in the vapour phase of one of its chemical components. We discuss how this physical situation allows for what would typically be a non-linear boundary value problem to be approximately reduced to a linear boundary value problem. For the case of aqueous aerosol particles, we investigate the accuracy of the closed-form analytical solution to this linear problem through a comparison with the numerical solution of the full problem. Then, using experimentally measured whispering gallery modes to track the frequency-dependent response of aqueous particles to relative humidity oscillations, we determine diffusion coefficients as a function of water activity. The measured diffusion coefficients are compared to previously reported values found using the two common experiments: (i) the analysis of the sorption/desorption of water from a particle after a step-wise change to the surrounding relative humidity and (ii) the isotopic exchange of water between a particle and the vapour phase. The technique presented here has two main strengths: first, when compared to the sorption/desorption experiment, it does not require the numerical evaluation of a boundary value problem during the fitting process as a closed-form expression is available. Second, when compared to the isotope exchange experiment, it does not require the use of labeled molecules. Therefore, the frequency-dependent experiment retains the advantages of these two commonly used methods but does not suffer from their drawbacks.
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Affiliation(s)
- Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University, 805 Sherbrooke Street West, Montreal, QC, Canada H3A 0B9.
| | - James F Davies
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94611, USA
| | - Kevin R Wilson
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94611, USA
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Abstract
Isotopic exchange experiments that utilize D2O and H2O have received attention as a method for studying water diffusion in high viscosity aerosol particles. However, the mathematical models used to retrieve diffusion coefficients from these measurements have yet to be critically examined. Here, two models for the isotopic exchange of D2O and H2O in spherical particles are analyzed and compared. The primary difference between the two models is the choice of boundary condition at the surface of the spherical particle. In one model, it is assumed that the concentration of D2O at the surface is fixed, while in the other model, it is assumed that, at the particle surface, the concentration of D2O in the condensed phase is in equilibrium with D2O vapor. Closed-form expressions for the two boundary value problems that describe these physical models are found and discussed. Then, specific examples of aqueous droplets containing either sucrose, citric acid, and shikimic acid are examined with both models. It is found that at low relative humidities the choice of boundary condition has a negligible effect on the predicted lifetime of isotopic exchange, while at high relative humidities predicted lifetimes can differ by orders of magnitude. The implication of this result is that the choice of model can greatly affect diffusion coefficients retrieved from experimental measurements under certain conditions. Finally, discrepancies between diffusion coefficients measured using isotopic exchange and water sorption and desorption experiments are discussed.
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Affiliation(s)
- Ali Moridnejad
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University , 805 Sherbrooke Street West, Montreal, QC Canada H3A 0B9
| | - Thomas C Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry, McGill University , 805 Sherbrooke Street West, Montreal, QC Canada H3A 0B9
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17
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Preston TC, Reid JP. Determining the size and refractive index of microspheres using the mode assignments from Mie resonances. J Opt Soc Am A Opt Image Sci Vis 2015; 32:2210-2217. [PMID: 26560936 DOI: 10.1364/josaa.32.002210] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A new method for determining the radius and refractive index of microspheres using Mie resonances is presented. Previous methods have relied on searching multidimensional space to find the radius and refractive index that minimize the difference between observed and calculated Mie resonances. For anything but simple refractive index functions, this process can be very time consuming. Here, we demonstrate that once the mode assignment for the observed Mie resonances is known, no search is necessary, and the radius and refractive index of best-fit can be found immediately. This superior and faster way to characterize microspheres using Mie resonances should supplant previous fitting algorithms. The derivation and implementation of the equations that give the parameters of best-fit are shown and discussed. Testing is performed on systems of physical interest, and the effect of noise on measured peak positions is investigated.
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18
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Preston TC, Reid JP. Angular scattering of light by a homogeneous spherical particle in a zeroth-order Bessel beam and its relationship to plane wave scattering. J Opt Soc Am A Opt Image Sci Vis 2015; 32:1053-1062. [PMID: 26367038 DOI: 10.1364/josaa.32.001053] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The angular scattering of light from a homogeneous spherical particle in a zeroth-order Bessel beam is calculated using a generalized Lorenz-Mie theory. We investigate the dependence of the angular scattering on the semi-apex angle of the Bessel beam and discuss the major features of the resulting scattering plots. We also compare Bessel beam scattering to plane wave scattering and provide criterion for when the difference between the two cases can be considered negligible. Finally, we discuss a method for characterizing spherical particles using angular light scattering. This work is useful to researchers who are interested in characterizing particles trapped in optical beams using angular dependent light scattering measurements.
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Rickards AMJ, Song YC, Miles REH, Preston TC, Reid JP. Variabilities and uncertainties in characterising water transport kinetics in glassy and ultraviscous aerosol. Phys Chem Chem Phys 2015; 17:10059-73. [DOI: 10.1039/c4cp05383d] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A comprehensive assessment of the accuracy with which water transport in viscous aerosol can be measured and predicted is provided.
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Affiliation(s)
| | | | | | - Thomas C. Preston
- School of Chemistry
- University of Bristol
- Bristol
- UK
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
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20
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Cotterell MI, Mason BJ, Preston TC, Orr-Ewing AJ, Reid JP. Optical extinction efficiency measurements on fine and accumulation mode aerosol using single particle cavity ring-down spectroscopy. Phys Chem Chem Phys 2015; 17:15843-56. [DOI: 10.1039/c5cp00252d] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We report a new single aerosol particle approach using cavity ringdown spectroscopy to accurately determine optical extinction cross sections at multiple wavelengths.
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Affiliation(s)
| | | | - Thomas C. Preston
- Department of Atmospheric and Oceanic Sciences and Department of Chemistry
- McGill University
- Montreal
- Canada
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21
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Dennis-Smither BJ, Marshall FH, Miles REH, Preston TC, Reid JP. Volatility and Oxidative Aging of Aqueous Maleic Acid Aerosol Droplets and the Dependence on Relative Humidity. J Phys Chem A 2014; 118:5680-91. [DOI: 10.1021/jp504823j] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
| | | | | | | | - Jonathan P. Reid
- School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
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Abstract
Light interacts surprisingly differently with small particles than with bulk or gas phase materials. This can cause rare phenomena such as the occurence of a "blue moon". Spectroscopic particle phenomena of similar physical origin have also spawned countless applications ranging from remote sensing to medicine. Despite the broad interest in particle spectra, their interpretation still poses many challenges. In this Account, we discuss the challenges associated with the analysis of infrared, or vibron, extinction spectra of small dielectric particles. The comparison with the more widely studied plasmon spectra of metallic nano-particles reveals many common features. The shape, size, and architecture of particles influence the band profiles in vibron and plasmon spectra in similar ways. However, the molecular structure of dielectric particles produces infrared spectral features that are more diverse and detailed or even unique to vibron spectra. More complexity means higher information content, but that also makes the spectra more difficult to interpret. Conventional models such as classical electromagnetic theory with a continuum description of the wavelength-dependent optical constants are often no longer applicable to these spectra. In cases where accurate optical constants are not available and for ultrafine particles, where the molecular structure and quantum effects become essential, researchers must resort to molecular models for light-particle interaction that do not require the prior knowledge of optical constants. In this Account, we illustrate how vibrational exciton approaches combined with molecular dynamics simulations and solid-state density functional calculations provide a viable solution to these challenges. Molecular models reveal two important characteristics of vibron spectra of small molecularly structured particles. The band profiles in vibron spectra are largely determined by transition dipole coupling between the molecules in a particle. Below a specific particle size limit, conventional models fail. Molecular models explain many other phenomena in particle spectra, such as size, shape, and mixing effects, providing the foundation for a better understanding of the interaction of solar radiation with aerosols and clouds and for the design of dielectric nanomaterials.
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Affiliation(s)
- Thomas C. Preston
- Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
| | - Ruth Signorell
- Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
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Affiliation(s)
- Thomas C. Preston
- a Department of Chemistry , University of British Columbia , 2036 Main Mall, Vancouver , BC, V6T 1Z1 , Canada
| | - Ruth Signorell
- a Department of Chemistry , University of British Columbia , 2036 Main Mall, Vancouver , BC, V6T 1Z1 , Canada
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Preston TC, Wang CC, Signorell R. Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles. J Chem Phys 2012; 136:094509. [PMID: 22401454 DOI: 10.1063/1.3690063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Aerosol particles composed of co-crystalline CO(2)·C(2)H(2) were generated in a bath gas cooling cell at cryogenic temperatures and investigated with infrared spectroscopy between 600 and 4000 cm(-1). Similar to results obtained for thin films of the co-crystal [T. E. Gough and T. E. Rowat, J. Chem. Phys. 109, 6809 (1998)], this phase was found to be metastable and decomposed into pure CO(2) and pure C(2)H(2). These decomposed aerosols were characterized through (i) a comparison to experimentally prepared aerosols of mixed CO(2) and C(2)H(2) of known architectures and (ii) the modeling of infrared spectra. A likely architecture after decomposition are C(2)H(2)-CO(2) core-shell particles with a disk-like shape. The co-crystalline CO(2)·C(2)H(2) aerosols prior to decomposition are modeled and analyzed in detail in the subsequent paper (Part II).
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Affiliation(s)
- Thomas C Preston
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
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Preston TC, Signorell R. Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. II. The structure and shape of co-crystalline CO2·C2H2 aerosol particles. J Chem Phys 2012; 136:094510. [DOI: 10.1063/1.3690064] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
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Preston TC, Signorell R. Formation of gold particles on nanoscale toroidal DNA assembled with bis(ethylenediamine)gold(III). Langmuir 2010; 26:10250-10253. [PMID: 20364858 DOI: 10.1021/la100402j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
DNA toroids formed by calf thymus DNA and trivalent cation bis(ethylenediamine)gold(III) are investigated using transmission electron microscopy and dynamic light scattering. Stable dispersions containing toroids with diameters of around 44 nm and thicknesses between 12 and 17 nm are readily prepared. These toroids are shown to be a robust platform for the preparation of metallic nanomaterials. Depending on the reaction conditions, the reduction of gold(III) in their presence can result in either toroids coated with many small (<10 nm) gold particles or larger continuous gold structures.
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Affiliation(s)
- Thomas C Preston
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 Canada.
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Preston TC, Firanescu G, Signorell R. Infrared spectroscopy and vibrational exciton modeling of crystalline, polycrystalline and amorphous acetylene aerosol particles. Phys Chem Chem Phys 2010; 12:7924-33. [DOI: 10.1039/c002525a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Preston TC, Signorell R. Growth and optical properties of gold nanoshells prior to the formation of a continuous metallic layer. ACS Nano 2009; 3:3696-3706. [PMID: 19785392 DOI: 10.1021/nn900883d] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The growth and optical properties of incomplete gold layers on silica particles (229 nm) are studied using visible/near-infrared spectroscopy and transmission electron microscopy. The gold particles that eventually coalesce to form a continuous gold layer are found to have droplet-like shapes. The optical properties of these systems are different from those of complete gold nanoshells. Using the discrete dipole approximation, it is found that the plasmon modes of such systems should exhibit two bands: one from 500-600 nm ("high energy") and the other from 600-800 nm ("low energy"). The calculations show that, for increasing coating density of the droplet-like particles, the lower energy band (i) becomes stronger relative to the higher energy band and (ii) is red-shifted. Both of these trends are found in the spectra of the prepared particles. Furthermore, the observed plasmon bands fall within the limits established by the model.
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Affiliation(s)
- Thomas C Preston
- Department of Chemistry, University of British Columbia, Vancouver, BC, Canada
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