Laboratory studies of collection efficiency of sub-micrometer aerosol particles by cloud droplets on a single-droplet basis

Abstract

Abstract. An experimental setup has been constructed to measure the collection efficiency (CE) of sub-micrometer aerosol particles by cloud droplets. Droplets of a dilute aqueous ammonium sulfate solution with an average radius of 21.6 µm fall freely into a chamber and collide with sub-micrometer polystyrene latex (PSL) sphere particles of known sizes and concentrations. Two relative humidity (RH) conditions, 15 ± 3 % and 88 ± 3 %, hereafter termed "low" and "high", respectively, were varied with different particles sizes and concentrations. After passing through the chamber, the droplets and aerosol particles were sent to the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument to determine chemical compositions on a single-droplet basis. "Coagulated droplets" (droplets that collected aerosols) had mass spectra that contained signatures from both an aerosol particle and a droplet residual. CE values range from 2.0 × 10 −1 to 1.6 for the low-RH case and from 1.5 × 10 −2 to 9.0 × 10 −2 for the high-RH case. CE values were, within experimental uncertainty, independent of the aerosol concentrations. CE values in this study were found to be in agreement with previous experimental and theoretical studies. To our knowledge, this is the first collection experiment performed on a single-droplet basis with atmospherically relevant conditions such as droplet sizes, droplet charges and flow.

On the limits of Köhler activation theory: how do collision and coalescence affect the activation of aerosols?

“…Moreover, the collection kernel might not incorporate all processes relevant for collections among aerosols and droplets. For instance, Brownian diffusion might increase the collection of smaller particles (e.g., Ardon-Dryer et al, 2015) but might not lead to collectional activation since it will predominantly add aerosol mass and only a small amount of water 8352 F. Hoffmann: Collectional activation (cf. Sect.…”

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

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Experimental evidence of the rear capture of aerosol particles by raindrops

“…Several mechanisms are usually considered, which are summarised hereafter; however, a more exhaustive review can be found in the literature (Pruppacher et al, 1998;Chate, 2005;Ladino et al, 2013;Ardon-Dryer et al, 2015). The three main mechanisms leading to this collection are Brownian motion, inertial impaction and interception.…”

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