Precision of light scattering techniques for measuring optical parameters of microspheres

Ak, Ray; Souyri, A.; Ej, Davis; Allen, Todd M.

doi:10.1364/ao.30.003974

Cited by 103 publications

(57 citation statements)

References 25 publications

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“…In general, the proportionality factor, K, depends on refractive index and Mie parameter, but Ray et al (1991) have shown that K(m D , X) varies between 0.94 and 0.96 for 1.30 ≤ m D ≤ 2.00 when the Mie parameter, X, is of the order of 100 as is the case in our experiments. In this study, we take K as a constant factor of 0.95.…”

Section: Conversion Of Mie Resonance Data To Size and Concentrationmentioning

confidence: 44%

“…These Mie resonances, also called whispering gallery modes, have been observed for both elastic (e.g., Chylek et al, 1983;Ray et al, 1991) and inelastic scattering (e.g., Conwell et al, 1984;Preston and Reid, 2013). Conventionally, those spectra have been measured using a fixed wavelength, while drying or humidifying a particle and hence changing its size.…”

Section: Methodsmentioning

confidence: 99%

“…A change in the real part of the refractive index from m D,0 to m D (t) leads to an additional shift in the wavelength of a mode in the Mie resonance spectrum (Ray et al, 1991). The combined effect can be accounted for by solving iteratively Eq.…”

Section: Conversion Of Mie Resonance Data To Size and Concentrationmentioning

confidence: 99%

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Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

Steimer

Krieger

et al. 2015

Atmos. Meas. Tech.

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Abstract. Measurements of a single, levitated particle in an electrodynamic balance are an established tool for deriving thermodynamic and material data such as density, refractive index and activities of components of an aqueous solution under supersaturated conditions, where bulk measurements are not possible. The retrieval relies on combining mass-tocharge data and size data from light scattering. Here, we use a combination of low-and high-resolution Mie resonance spectroscopy to obtain radius data, enabling an accurate size determination not only when the particle is in equilibrium, but also when it is out of equilibrium due to kinetic limitation of mass transport. With the data measured under nonequilibrium conditions, it is possible to retrieve the water diffusivity. A challenge is that the radius retrieval by comparing measured light scattering with Mie theory requires the knowledge of refractive index as a function of concentration. Here, we show an iterative retrieval of refractive index and size for compounds for which data cannot be obtained in the bulk either due to lack of sufficient amounts of sample or limited solubility. We demonstrate the measurement strategy and the retrieval of water activity, density, refractive index and water diffusivity for aqueous shikimic acid. Water diffusivity in concentrated shikimic acid decreases by 6 orders of magnitude at 250 K compared to that at room temperature.

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Section: Conversion Of Mie Resonance Data To Size and Concentrationmentioning

confidence: 44%

Section: Methodsmentioning

confidence: 99%

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Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

Steimer

Krieger

et al. 2015

Atmos. Meas. Tech.

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“…where K(m(t), χ ) assumes values between 0.94 and 0.95 for 1.30 ≤ m ≤ 2.00 and χ ∼ 100 (Ray et al, 1991). Here, K was treated as a constant and set to 0.95.…”

Section: Processing Of Led Spectramentioning

confidence: 99%

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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“…By fitting measured scattering diagrams (i.e., continuous scattered intensity vs. scattering angle 0) to those generated with Lorenz-Mie theory, particle diameter could be determined generally within 1% and real refractive index with a precision of 0.01. Mofe recently, Chylek et al (1983) and Ray et al (1991) have utilized the rich optical resonance spectra implicit in Mie theory solutions to infer diameters and real refractive indices of spherical dielectric particles > 1 p m with relative errors of 5 x lop5. These measurements involve DLS measurements on levitated spheres in which particle size, scattering angle, or wavelength were varied to produced resonance.…”

Section: Introductionmentioning

confidence: 99%

Size- and Composition-Dependent Response of the DAWN-A Multiangle Single-Particle Optical Detector

Dick

McMurry

Bottiger

1994

Aerosol Science and Technology

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The performance of the DAWN-A differential lightscattering detector (Wyatt et al., 1988. Appl. Opt. 27:217-221) was characterized in laboratory experiments. Objectives of this work included measurement of size-dependent counting efficiencies and of angular scattering patterns for spherical particles of known size and composition.Counting efficiencies for polystyrene latex (PSL) spheres of nine sizes in the 0.14-0.97-pm diameter range were obtained as a function of the trigger threshold level. Counting efficiencies were found to increase with increasing particle size and decreasing trigger threshold level. Maximum observed counting efficiencies were in the range of 50% to 60%, indicating that the half-width of the laser beam was about a factor of 2 narrower than the width of the particle beam in the scattering volume. A distribution of pulse heights was observed for particles of a given size, reflecting the variability of the illumination intensity.Angular scattering patterns of PSL, dioctyl sehacate (DOS), and methylene blue for nine different sizes in the 0.14-0.97-pm size range were obtained; measurements were also done with 0.55-pm (at 7% relative humidity) sulfuric acid droplets exposed to eight different relative humidities in the 7% to 81% range. The PSL data were used to calibrate the detectors. For the other materials, Lorenz-Mie theory was used to determine the "best" value of the complex refractive index to match measurements to theory for each particle size investigated. For sulfuric acid, the inferred imaginary component of refractive index was zero as expected, while the real component was within 2% of the literature value over the range of relative humidities investigated. For DOS (expected value = 1.46 + O.OOi), the inferred real component of refractive index was, on average, 4% greater than the expected value, and the average inferred imaginary component was 0.02 for particles >0.32 pm. Small signal-to-noise led to poor agreement between theory and measurement for 0.14-p m particles. For methylene blue, which has a nonzero imaginary component (expected value = 0.82 + 0.40i), there were large uncertainties in the inferred refractive index values due to problems in generating spherical, homogeneous particles.

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Precision of light scattering techniques for measuring optical parameters of microspheres

Cited by 103 publications

References 25 publications

Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

Diffusivity measurements of volatile organics in levitated viscous aerosol particles

Size- and Composition-Dependent Response of the DAWN-A Multiangle Single-Particle Optical Detector

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