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

Santachiara, Gianni; Prodi, F.; Belosi, Franco

doi:10.4236/acs.2012.22016

Cited by 25 publications

(30 citation statements)

References 80 publications

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“…The combined description of thermophoretic and diffusiophoretic forces indicate that for our experimental conditions of evaporating droplets in the presence of rather small aerosol particles, thermophoresis should exceed diffusiophoresis (Slinn and Hales, 1971). However, disagreement still exists between experiments and model predictions concerning the prevalent forces as a function of particle radius (Santachiara et al, 2012;Prodi et al, 2014). Figure 7 shows the droplet charge dependence of electroscavenging for the formulations of A06 and W78.…”

Section: Temperature Dependence Of Thermophoretic Collision Efficiencymentioning

confidence: 89%

“…Aerosol scavenging is usually described by the scavenging coefficient (s −1 ) defined as the rate of aerosol removal (Chate et al, 2011). In field measurements, the scavenging coefficient is usually calculated from measurements of the change in aerosol size distribution with rainfall (Santachiara et al, 2012). For very small and very large particles, there is mainly an agreement with theoretical studies.…”

Section: Implications For Atmospheric Aerosol Scavengingmentioning

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: Temperature Dependence Of Thermophoretic Collision Efficiencymentioning

confidence: 89%

Section: Implications For Atmospheric Aerosol Scavengingmentioning

confidence: 99%

Comparison of measured and calculated collision efficiencies at low temperatures

et al. 2015

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“…Note that other potential collection mechanisms such as diffusiophoresis, thermophoresis, and electric charges are not included in these formulas. For rain scavenging of atmospheric aerosols, these several mechanisms are less important than the three major mechanisms discussed above and are only significant for particles in the size range of 0.01-1.0 µm (Tinsley et al, 2000;Wang et al, 2010;Santachiara et al, 2012). This is also expected to be the case for snow scavenging of aerosols.…”

Section: Sensitivity Of Snow To Ementioning

confidence: 95%

Review and uncertainty assessment of size-resolved scavenging coefficient formulations for below-cloud snow scavenging of atmospheric aerosols

Zhang

Wang²,

Moran

et al. 2013

Atmos. Chem. Phys.

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Abstract. Theoretical parameterizations for the sizeresolved scavenging coefficient for atmospheric aerosol particles scavenged by snow ( snow ) need assumptions regarding (i) snow particle-aerosol particle collection efficiency E, (ii) snow-particle size distribution N(D p ), (iii) snow-particle terminal velocity V D , and (iv) snow-particle cross-sectional area A. Existing formulas for these parameters are reviewed in the present study, and uncertainties in snow caused by various combinations of these parameters are assessed. Different formulations of E can cause uncertainties in snow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. E is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols ( rain ) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in snow , and the uncertainties from these parameters are much larger than for rain . Specifically, different N(D p ) formulations can cause one-order-of-magnitude uncertainties in snow for all aerosol sizes, as is also the case for a combination of uncertainties from both V D and A. Assumptions about dominant snowparticle shape (and thus different V D and A) will cause an uncertainty of up to one order of magnitude in the calculated scavenging coefficient. In comparison, uncertainties in rain from N (D p ) are smaller than a factor of 5, and those from V D are smaller than a factor of 2. As expected, snow estimated from empirical formulas generated from field measurements falls in the upper range of, or is higher than, the theoretically estimated values, which can be explained by additional processes/mechanisms that influence field-derived snow but that are not considered in the theoretical snow formulas. Predicted aerosol concentrations obtained by using upper range vs. lower range of snow values (a difference of around two orders of magnitude in snow ) can differ by a factor of 2 for just a one-centimetre snowfall (liquid water equivalent of approximately 1 mm). Based on the median and upper range of theoretically generated snow and snow values, it is likely that, for typical rain and snow events, the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence.

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“…Oeste (2004) suggested and Wittmer et al (2015a and Figure 2 illustrates this climate cooling mechanism by the ISA method with a simplified chemical reaction scheme: a direct cooling of the troposphere by CH 4 oxidation induced by ISA particles. At droplet or particle diameters below 1 µm (between 1 and 0.1 µm), contact or coagulation actions between the particles within aerosol clouds are retarded (Ardon-Dryer et al, 2015;Rosenfeld and Freud, 2011;Santachiara et al, 2012;Wang et al, 1978). Otherwise the aerosol lifetime would be too short to bridge any intercontinental distance or arrive in polar regions.…”

Section: Oxidation Of Methane and Other Ghgsmentioning

confidence: 99%

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

et al. 2017

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Abstract. Power stations, ships and air traffic are among the most potent greenhouse gas emitters and are primarily responsible for global warming. Iron salt aerosols (ISAs), composed partly of iron and chloride, exert a cooling effect on climate in several ways. This article aims firstly to examine all direct and indirect natural climate cooling mechanisms driven by ISA tropospheric aerosol particles, showing their cooperation and interaction within the different environmental compartments. Secondly, it looks at a proposal to enhance the cooling effects of ISA in order to reach the optimistic target of the Paris climate agreement to limit the global temperature increase between 1.5 and 2 • C.Mineral dust played an important role during the glacial periods; by using mineral dust as a natural analogue tool and by mimicking the same method used in nature, the proposed ISA method might be able to reduce and stop climate warming. The first estimations made in this article show that by doubling the current natural iron emissions by ISA into the troposphere, i.e., by about 0.3 Tg Fe yr −1 , artificial ISA would enable the prevention or even reversal of global warming. The ISA method proposed integrates technical and economically feasible tools.

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

Cited by 25 publications

References 80 publications

Comparison of measured and calculated collision efficiencies at low temperatures

Comparison of measured and calculated collision efficiencies at low temperatures

Review and uncertainty assessment of size-resolved scavenging coefficient formulations for below-cloud snow scavenging of atmospheric aerosols

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

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