Parameterization of Aerosol Scavenging Due to Atmospheric Ionization Under Varying Relative Humidity

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Parameterization of Aerosol Scavenging Due to Atmospheric Ionization Under Varying Relative Humidity

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Title: Parameterization of Aerosol Scavenging Due to Atmospheric Ionization Under Varying Relative Humidity
Author(s):
Zhang, Liang;
Tinsley, Brian A.
Date Created: 2017-04-12
Item Type: article
Keywords: Show Keywords
Abstract: Simulations and parameterizations of the modulation of aerosol scavenging by electric charges on particles and droplets for different relative humidities have been made for 3 mu m radii droplets and a wide range of particle radii. For droplets and particles with opposite-sign charges, the attractive Coulomb force increases the collision rate coefficients above values due to other forces. With same-sign charges, the repulsive Coulomb force decreases the rate coefficients, and the short-range attractive image forces become important. The phoretic forces are attractive for relative humidity less than 100% and repulsive for relative humidity greater than 100% and have increasing overall effect for particle radii up to about 1 mu m. There is an analytic solution for rate coefficients if only inverse square forces are present, but due to the presence of image forces, and for larger particles the intercept, weight, and the flow around the particle affecting the droplet trajectory, the simulated results usually depart far from the analytic solution. We give simple empirical parameterization formulas for some cases and more complex parameterizations for more exact fits to the simulated results. The results can be used in cloud models with growing droplets, as in updrafts, as well as with evaporating droplets in downdrafts. There is considered to be little scavenging of uncharged ice-forming nuclei in updrafts, but with charged ice-forming nuclei it is possible for scavenging in updrafts in cold clouds to produce contact ice nucleation. Scavenging in updrafts below the freezing level produces immersion nuclei that promote enhanced freezing as droplets rise above it.
Publisher: Amer Geophysical Union
ISSN: 2169-897X
Source: Journal of Geophysical Research--Atmospheres
Link to Related Resource: http://dx.doi.org/10.1002/2016JD026255
Persistent Link: http://hdl.handle.net/10735.1/6143
Bibliographic Citation: Zhang, Liang, and Brian A. Tinsley. 2017. "Parameterization of aerosol scavenging due to atmospheric ionization under varying relative humidity." Journal of Geophysical Research--Atmospheres 122(10), doi:10.1002/2016JD026255
Terms of Use: ©2017 American Geophysical Union. All Rights Reserved.
Sponsors: U.S. National Science Foundation grant AGS 0836171

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