Time-Resolved Measurements of the Evaporation of Volatile Components from Single Aerosol Droplets

Davies, James F.; Haddrell, Allen E.; Reid, Jonathan P.

doi:10.1080/02786826.2011.652750

Cited by 106 publications

(155 citation statements)

References 51 publications

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“…44 The mass transfer enhancement resulting from the flowing gas surrounding the droplet is accounted for by the inclusion of a Sherwood number (Sh) scaling of the mass flux. 33,43 The thermophysical parameters that appear in the mass flux treatment and their uncertainties have been thoroughly discussed in previous publications. 32,34,45,46 The resulting expression for the mass flux is the following:…”

Section: Methodsmentioning

confidence: 99%

“…There is a time period (∼0.1 s) between droplet generation and the first determination of size when the droplet is in transit into the trapping region. 32,33 Thus, the initial size of the droplet is estimated with a linear extrapolation of the a 2 vs time plot to t = 0 s; the initial solute mass fraction and density of solute solution at t = 0 s and at this droplet size are known from the prepared solution. 33 The elastic light scattering data are first analyzed with m = 1.335 to yield an initial estimate of the variation in radius with time, also providing a first estimate of the variation of the solute concentration and of the solution density during the evaporation.…”

Section: Methodsmentioning

confidence: 99%

“…32,33 Thus, the initial size of the droplet is estimated with a linear extrapolation of the a 2 vs time plot to t = 0 s; the initial solute mass fraction and density of solute solution at t = 0 s and at this droplet size are known from the prepared solution. 33 The elastic light scattering data are first analyzed with m = 1.335 to yield an initial estimate of the variation in radius with time, also providing a first estimate of the variation of the solute concentration and of the solution density during the evaporation. A set of corrected refractive indices for the droplet solution at every time step is then calculated on the basis of the change in size using the molar refraction mixing rule (eqs 2−4).…”

Section: Methodsmentioning

confidence: 99%

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Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

et al. 2016

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Using a comparative evaporation kinetics approach, we describe a new and accurate method for determining the equilibrium hygroscopic growth of aerosol droplets. The time-evolving size of an aqueous droplet, as it evaporates to a steady size and composition that is in equilibrium with the gas phase relative humidity, is used to determine the time-dependent mass flux of water, yielding information on the vapor pressure of water above the droplet surface at every instant in time. Accurate characterization of the gas phase relative humidity is provided from a control measurement of the evaporation profile of a droplet of know equilibrium properties, either a pure water droplet or a sodium chloride droplet. In combination, and by comparison with simulations that account for both the heat and mass transport governing the droplet evaporation kinetics, these measurements allow accurate retrieval of the equilibrium properties of the solution droplet (i.e., the variations with water activity in the mass fraction of solute, diameter growth factor, osmotic coefficient or number of water molecules per solute molecule). Hygroscopicity measurements can be made over a wide range in water activity (from >0.99 to, in principle, <0.05) on time scales of <10 s for droplets containing involatile or volatile solutes. The approach is benchmarked for binary and ternary inorganic solution aerosols with typical uncertainties in water activity of <±0.2% at water activities >0.9 and ∼±1% below 80% RH, and maximum uncertainties in diameter growth factor of ±0.7%. For all of the inorganic systems examined, the time-dependent data are consistent with large values of the mass accommodation (or evaporation) coefficient (>0.1).

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

et al. 2016

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“…We have discussed previously the applicability of this model in the interpretation of our measurements (5,11,13,38). The transition regime correction factors of Fuchs-Sutugin are used to account for the marked reduction in the continuum mass and heat fluxes observed due to the slow interfacial transfer kinetics and the considerable diminution of the evaporation coefficient when an organic film is formed.…”

Section: Methodsmentioning

confidence: 99%

“…The experimental technique has been discussed by us previously and will be only briefly reviewed here (5,38). The sample solution is placed in the reservoir of a microdispenser (Microfab MJ-ABP-01; 30-μm orifice).…”

Section: Methodsmentioning

confidence: 99%

Influence of organic films on the evaporation and condensation of water in aerosol

Davies

Miles

Haddrell

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Uncertainties in quantifying the kinetics of evaporation and condensation of water from atmospheric aerosol are a significant contributor to the uncertainty in predicting cloud droplet number and the indirect effect of aerosols on climate. The influence of aerosol particle surface composition, particularly the impact of surface active organic films, on the condensation and evaporation coefficients remains ambiguous. Here, we report measurements of the influence of organic films on the evaporation and condensation of water from aerosol particles. Significant reductions in the evaporation coefficient are shown to result when condensed films are formed by monolayers of long-chain alcohols [C n H (2n+1) OH], with the value decreasing from 2.4 × 10 −3 to 1.7 × 10 −5 as n increases from 12 to 17. Temperature-dependent measurements confirm that a condensed film of long-range order must be formed to suppress the evaporation coefficient below 0.05. The condensation of water on a droplet coated in a condensed film is shown to be fast, with strong coherence of the long-chain alcohol molecules leading to islanding as the water droplet grows, opening up broad areas of uncoated surface on which water can condense rapidly. We conclude that multicomponent composition of organic films on the surface of atmospheric aerosol particles is likely to preclude the formation of condensed films and that the kinetics of water condensation during the activation of aerosol to form cloud droplets is likely to remain rapid.water transport | organic monolayers | mass accommodation | surface films T he transport of volatile and semivolatile components between the condensed and gas phases in aerosol during evaporation or condensation is important for understanding cloud microphysics, atmospheric chemistry, the delivery of drugs to the lungs, and the applications of aerosols in materials and combustion science. For example, the uptake of chemical species to atmospheric aerosol particles facilitates chemical reactions (1), the condensation of water on cloud condensation nuclei allows cloud droplets to form (2), the uptake of water on pharmaceutical aerosol can affect their deposition pattern within the lungs (3), and the evaporation rates of solvents in spray drying processes influence the structure and morphology of the final microparticle (4). The rate of mass transport to or from an aerosol particle can be considered to involve the interplay of three mechanistic steps: gas phase diffusion, interfacial transfer, and bulk condensed phase diffusion. Different limiting regimes can be identified under which the rate of evaporation or condensation is determined by any one of these steps (5).The Knudsen number is the ratio of the mean free path of gas phase molecules to the particle radius. At low Knudsen number, in the limits of large particle size and high gas pressure, gas phase diffusion usually determines evaporation and condensation rates. Bulk phase diffusion is limiting when the viscosity of the particle impedes transport to or from the surfac...

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Temperature dependence of the vapor pressure and evaporation coefficient of supercooled water

Davies

Miles

Haddrell

et al. 2014

J. Geophys. Res. Atmos.

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We report measurements of the vapor pressure of water over the supercooled temperature range 248 to 273 K derived from evaporation kinetics measurements of single water droplets. Accurate measurements of the relative humidity of the surrounding gas phase are derived from comparative and sequential measurements of the evaporation kinetics of droplets containing sodium chloride. The temperature dependence of the vapor pressure of supercooled water is shown to conform closely to the parameterization provided by Murphy and Koop (2005) once the uncertainties in experimental and thermophysical parameters are accounted for by ensuring an accurate representation of evaporation rates at temperatures above 273 K. Further, from a sensitivity analysis of all of the data over the full temperature range from 248 to 293 K, we can conclude that the evaporation coefficient of water, and thus the mass accommodation coefficient, is greater than, or equal to, 0.5.

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Time-Resolved Measurements of the Evaporation of Volatile Components from Single Aerosol Droplets

Cited by 106 publications

References 51 publications

Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

Influence of organic films on the evaporation and condensation of water in aerosol

Temperature dependence of the vapor pressure and evaporation coefficient of supercooled water

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