Relative contributions of individual phoretic effect in the below-cloud scavenging process

Bae, Sung‐Heui; Jung, Chang Hoon; Kim, Yong Pyo

doi:10.1016/j.jaerosci.2009.03.003

Cited by 35 publications

(27 citation statements)

References 11 publications

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“…Many theoretical studies on scavenging do not take phoretic forces into account, but even those which do are not able to explain the discrepancies between field and observed scavenging coefficients in the Greenfield gap (Santachiara et al, 2012). Most model parameterizations treat the collision processes separately and either assume that they act in series (Davenport and Peters, 1978) or calculate the total collision efficiency as the sum of individual collision efficiencies (Bae et al, 2009;Andronache et al, 2006). With this approach, the net effect of repulsive and attractive contributions of forces acting on particles cannot be taken into account correctly.…”

Section: Implications For Atmospheric Aerosol Scavengingmentioning

confidence: 99%

“…In models, collision efficiencies are usually calculated as the sum of the different collision processes (Andronache et al, 2006;Bae et al, 2009;Croft et al, 2010) neglecting that the forces act together to determine the aerosol path either into or around the droplet. Trajectory calculations can be used to simulate the particle pathway; however, they need to be validated with reliable laboratory measurements (Tinsley and Leddon, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Comparison of measured and calculated collision efficiencies at low temperatures

et al. 2015

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Abstract.Interactions of atmospheric aerosols with clouds influence cloud properties and modify the aerosol life cycle. Aerosol particles act as cloud condensation nuclei and ice nucleating particles or become incorporated into cloud droplets by scavenging. For an accurate description of aerosol scavenging and ice nucleation in contact mode, collision efficiency between droplets and aerosol particles needs to be known. This study derives the collision rate from experimental contact freezing data obtained with the ETH CoLlision Ice Nucleation CHamber (CLINCH). Freely falling 80 µm diameter water droplets are exposed to an aerosol consisting of 200 and 400 nm diameter silver iodide particles of concentrations from 500 to 5000 and 500 to 2000 cm −3 , respectively, which act as ice nucleating particles in contact mode. The experimental data used to derive collision efficiency are in a temperature range of 238-245 K, where each collision of silver iodide particles with droplets can be assumed to result in the freezing of the droplet. An upper and lower limit of collision efficiency is also estimated for 800 nm diameter kaolinite particles. The chamber is kept at ice saturation at a temperature range of 236 to 261 K, leading to the slow evaporation of water droplets giving rise to thermophoresis and diffusiophoresis. Droplets and particles bear charges inducing electrophoresis. The experimentally derived collision efficiency values of 0.13, 0.07 and 0.047-0.11 for 200, 400 and 800 nm particles are around 1 order of magnitude higher than theoretical formulations which include Brownian diffusion, impaction, interception, thermophoretic, diffusiophoretic and electric forces. This discrepancy is most probably due to uncertainties and inaccuracies in the description of thermophoretic and diffusiophoretic processes acting together. This is, to the authors' knowledge, the first data set of collision efficiencies acquired below 273 K. More such experiments with different droplet and particle diameters are needed to improve our understanding of collision processes acting together.

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Section: Implications For Atmospheric Aerosol Scavengingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comparison of measured and calculated collision efficiencies at low temperatures

et al. 2015

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“…Nevertheless, the mechanisms of below-cloud scavenging, including the effect of inertia, Brownian diffusion, thermophoresis, diffusiophoresis and electro-scavenging, have been thoroughly recognized and described [2,4,[8][9][10][11][12][13][14]. One paper [15] in particular contains formulae that enable the researcher to assess the effectiveness of the particular mechanisms in the processes of below-cloud scavenging of aerosols.…”

Section: Introductionmentioning

confidence: 99%

Concentration Changes Of PM₁₀ Under Liquid Precipitation Conditions

Olszowski

2015

Ecological Chemistry and Engineering S

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This study reports the results of field research into variability of the scavenging coefficient (Λ) of suspended dust comprising particles with aerodynamic diameters less than 10 mm. Registration of PM10 over 7 years in conditions of the occurrence of rainfall (convective light showers, large-scale precipitation and storms) was undertaken in an undeveloped rural area. The analysis involved 806 observations taken at constant time intervals of 0.5 hour. The measurements of the concentration of PM10 were performed by means of a reference method accompanied by concurrent registration of basic meteorological parameters. It was found that, for PM10, the scavenging efficiency is considerably influenced by rainfall intensity R and the type of precipitation. In the case of convective precipitation, data on Λ are only partially related to "classical approach" of rain scavenging. Within the range of comparable values of rainfall intensity, the type of wet deposition (except for storms) does not influence the effectiveness of scavenging PM10 from the ground-level zone. The large number of observations conducted in real-time conditions yielded a proposal of simple regression model, which can be deemed suitable for the description of variability Λ (DPM10), but only to a limited extent for large-scale precipitation. The collected results can be applied in air pollution dispersion models and deposition and were found to be generally representative for areas with similar climatic characteristics.

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“…Chate [52], Andronache et al, [32], Bae et al, [33], chose the Davenport and Peters formula to evaluate the phoretic contribution, and assumed a constant difference temperature between surface drop and air, by neglecting the contribution of evaporation or condensation of water vapour to the temperature droplet. In order to interpret the data on scavenging coefficients determined from observations of ultrafine particles (with diameters in the range 0.01 μm -0.5 μm) by Laakso et al, [53], Andronache et al, [32] developed a simplified scavenging model, which includes below-cloud scavenging processes and mixing of ultrafine particles from the boundary layer into cloud followed by cloud condensation nuclei activation, and in-cloud removal by rainfall.…”

Section:   U Dmentioning

confidence: 99%

A Review of Termo- and Diffusio-Phoresis in the Atmospheric Aerosol Scavenging Process. Part 1: Drop Scavenging

Santachiara¹,

Prodi²,

Belosi³

2012

ACS

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The role of phoretic forces in providing in-cloud and below-cloud scavenging due to falling drop is reviewed by considering published papers dealing with theoretical models, laboratory and field measurements. Theoretical analyses agree that Brownian diffusion appears to dominate drop scavenging of aerosol with radius less than 0.1 μm, and inertial impaction dominates scavenging of aerosol with radius higher than 1 μm. Thus, there is a minimum collection efficiency for particles in the approximate range 0.1 μm -1 μm, where phoretic forces are felt. Generally speaking, published papers report not uniform evaluations of the contribution of thermo-and diffusiophoretic forces. This disagreement is partially due to the different laboratory and field conditions, and different theoretical approaches.

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Relative contributions of individual phoretic effect in the below-cloud scavenging process

Cited by 35 publications

References 11 publications

Comparison of measured and calculated collision efficiencies at low temperatures

Comparison of measured and calculated collision efficiencies at low temperatures

Concentration Changes Of PM₁₀ Under Liquid Precipitation Conditions

A Review of Termo- and Diffusio-Phoresis in the Atmospheric Aerosol Scavenging Process. Part 1: Drop Scavenging

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Relative contributions of individual phoretic effect in the below-cloud scavenging process

Cited by 35 publications

References 11 publications

Comparison of measured and calculated collision efficiencies at low temperatures

Comparison of measured and calculated collision efficiencies at low temperatures

Concentration Changes Of PM10 Under Liquid Precipitation Conditions

A Review of Termo- and Diffusio-Phoresis in the Atmospheric Aerosol Scavenging Process. Part 1: Drop Scavenging

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Product

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About

Concentration Changes Of PM₁₀ Under Liquid Precipitation Conditions