Real refractive index: Dependence on relative humidity and solute composition with relevancy to atmospheric aerosol particles

Wang, Wei; Rood, Mark J.

doi:10.1029/2008jd010165

Cited by 9 publications

(4 citation statements)

References 33 publications

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“…Therefore, it is important to note that the n value of dry particles are typically converted to the corresponding value for humidified particles using a volume‐weighted mixing rule approach using the refractive index of water (e.g., Levoni et al, ; Shettle & Fenn, ). Past measurement studies of ambient aerosol particles have reported a wide range of n values, usually between 1.4 and 1.6, with variability attributed to instrument wavelength, dry particle size, air mass type, and composition (e.g., Dubovik et al, ; Ferrare et al, ; Guyon et al, ; Wang & Rood, ). There is a limited inventory of vertically resolved n data (e.g., Raut & Chazette, ), which is needed to quantify aerosol effects on vertical temperature profiles, convection and redistribution of pollutants, and large‐scale circulation patterns.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Real Part of Dry Aerosol Refractive Index Over North America From the Surface to 12 km

et al. 2018

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This study reports a characterization of the real part of dry particle refractive index (n) at 532 nm based on airborne measurements over the United States, Canada, the Pacific Ocean, and the Gulf of Mexico from the 2012 Deep Convective Clouds and Chemistry (DC3) and 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC 4 RS) campaigns. Effective n values are reported, with the limitations and uncertainties discussed. Eight air mass types were identified based on criteria related to gas-phase tracer concentrations, location, and altitude. Average values of n for these air types ranged from 1.50 to 1.53. Values of n for the organic aerosol (OA) fraction (n OA ) were calculated using a linear mixing rule for each air mass type, with 1.52 shown to be a good approximation for all OA. Case studies detailing vertical structure revealed that n and n OA increased with altitude, simultaneous with enhancements in the mass fraction of OA. Values of n OA were positively (negatively) correlated with the O:C (H:C) ratio in the absence of biomass burning influence; in contrast, the cumulative data set revealed a slight decrease in n OA as a function of the O:C ratio. The performance of parametric (multiple linear regression) and nonparametric (Gaussian process regression) methods in predicting n based on aerosol composition data is discussed. It is shown that even small perturbations in n values significantly impact aerosol optical depth retrievals, radiative forcing, and optical sizing instruments, emphasizing the importance of further improving the understanding of this important aerosol property.

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Section: Introductionmentioning

confidence: 99%

Characterization of the Real Part of Dry Aerosol Refractive Index Over North America From the Surface to 12 km

et al. 2018

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“…2.1.2), a constant m value of 1.45 + i0 was selected to simulate sea spray particle scattering. This value is lower than the average refractive index reported for dry sea salt (real component = 1.5-1.6, imaginary component < 10 −6 ) (Wang and Rood, 2008;Randles et al, 2004;Bi et al, 2018) and was calculated as a mass-weighted mixture of salt with water, where water has a refractive index of 1.33 (Wang and Rood, 2008) (Sect. S2).…”

Section: Simulating Sea Spray Mode Scattering Using Mie Theorymentioning

confidence: 74%

Retrieval of the sea spray aerosol mode from submicron particle size distributions and supermicron scattering during LASIC

et al. 2022

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Abstract. Improved quantification of sea spray aerosol concentration and size is important for determining aerosol effects on clouds and the climate, though attempts to accurately capture the size distribution of the sea spray mode remain limited by the availability of supermicron size distributions. In this work, we introduce a new approach to retrieving lognormal mode fit parameters for a sea spray aerosol mode by combining submicron size distributions with supermicron scattering measurements using a Mie inversion. Submicron size distributions were measured by an ultra-high-sensitivity aerosol spectrometer (UHSAS), and supermicron scattering was taken as the difference between <10 µm and <1 µm three-wavelength integrating nephelometer measurements (NEPH). This UHSAS-NEPH method was applied during background marine periods of the Department of Energy Atmospheric Radiation Measurement Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign on Ascension Island (November 2016–May 2017), when the contribution of sea spray aerosol was expected to represent a large fraction of the aerosol mass and total scattering. Lognormal sea spray modal parameters were retrieved from comparisons between nephelometer measurements and a lookup table of Mie theory-simulated scattering coefficients for low-error solutions that minimized the 0.4–1 µm residual in the UHSAS size distribution. We evaluated the UHSAS-NEPH method with a set of clean marine measurements in the North Atlantic that included supermicron size and chemical measurements, showing that measured supermicron size distributions are needed to constrain the sea spray number concentration but that mass concentration was reasonably characterized using supermicron scattering. For LASIC, the UHSAS-NEPH method retrieved sea spray mode properties for approximately 88 % of the background marine times when the scattering variability and total particle concentration were low (<± 5 Mm−1 and <400 cm−3, respectively), with mass mean diameter ranging from 0.6 to 1.9 µm (1.47 ± 0.17 µm), modal width ranging from 1.1 to 3.97 (2.4±0.3), and mass concentration ranging from 0.18 to 23.0 µg m−3 (8.37. ± 4.1 µg m−3). The measured nephelometer scattering at three wavelengths was found to constrain the mode width marginally at the largest particle sizes in the absence of additional size and chemical measurements for defining parameters for the Mie solutions. Comparing UHSAS-NEPH retrievals to those of a fitting algorithm applied only to the submicron UHSAS number size distribution showed that correlations between retrieved mass concentration and the available mass-based sea spray tracers (coarse scattering, wind speed, and chloride) are low when supermicron measurements are not considered. This work demonstrates the added value of supermicron scattering measurements for retrieving reasonable sea spray mass concentrations, providing the best-available observationally constrained estimate of the sea spray mode properties when supermicron size distribution measurements are not available.

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“…60,61 For the multi-reflection ATR hardware considered in this work where a 4 mm-thick ZnSe IRE is used, y ¼ 45 , N ¼ 10, and n 1 ¼ 2.43. n 2 for organic compounds vary only within a small range (n 2 ¼ 1.4-1.5) 65,66 and are close to inorganic substances, e.g., 1.54 for NaCl, 1.53 for (NH 4 ) 2 SO 4 , 1.61 for NH 4 NO 3 , 1.56 for CaCO 3 , and 1.46 for SiO 2 , commonly found in atmospheric particles. 19,[67][68][69] Some additional uncertainty may be introduced through film porosity resulting from the deposition process, but overall, the dependence of A on variations in n 2 is expected to be small. For this range of refractive indices, the approximate d p of typical atmospheric PM constituents is 1 mm, 70 with the thin-film approximation applicable for samples in the range of d ¼ 50-100 nm.…”

Section: Attenuated Total Reflection Fourier Transform Infrared Spectmentioning

confidence: 99%

Electrospray Film Deposition for Solvent-Elimination Infrared Spectroscopy

et al. 2019

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The application of electrospray (ES) for quantitative transfer of analytes from solution to an internal reflection element for analysis by attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy has been developed in this work. The ES ATR FT-IR method is evaluated with non-volatile and semi-volatile organic and inorganic compounds dissolved in pure organic solvents or organics in a mixture with water. The technique demonstrates the capability for rapid solvent evaporation from dilute solutions, facilitating the creation of thin films that allow ATR FT-IR to generate transmission-mode-like spectra. Electrospray ATR FT-IR with multiple reflections displays a linear response (R 2 ¼ 0.95-0.99) in absorbance with the deposited mass and instrumental detection limit < 100 ng, which demonstrates potential for quantitative applications. The method is applicable when crystalline substances are present, even though the formation of particles restricts the upper limit of mass loadings relative to substances forming homogeneous films. In addition to the solvent, semi-volatile compounds can evaporate during the ES process; the magnitude of losses will depend on solution composition and temperature.

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Real refractive index: Dependence on relative humidity and solute composition with relevancy to atmospheric aerosol particles

Cited by 9 publications

References 33 publications

Characterization of the Real Part of Dry Aerosol Refractive Index Over North America From the Surface to 12 km

Characterization of the Real Part of Dry Aerosol Refractive Index Over North America From the Surface to 12 km

Retrieval of the sea spray aerosol mode from submicron particle size distributions and supermicron scattering during LASIC

Electrospray Film Deposition for Solvent-Elimination Infrared Spectroscopy

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