Abstract
Abstract. A new In-Cloud Aerosol Scavenging Experiment (In-CASE) has been developed to
measure the collection efficiency (CE) of submicron aerosol particles by
cloud droplets. Droplets fall at their terminal velocity through a
1 m high chamber in a laminar flow containing aerosol particles. At
the bottom of the In-CASE chamber, the droplet train is separated from the
aerosol particles flow, and the droplets are collected in an impaction cup,
whereas aerosol particles are deposited on a high-efficiency
particulate air (HEPA) filter. The collected droplets and the filter are then analysed
by fluorescence spectrometry since the aerosol particles are atomised from a
sodium fluorescein salt solution (C20H10Na2O5). In-CASE
fully controls all the parameters which affect the CE – the droplets and
aerosol particles size distributions are monodispersed, the electric charges
of droplets and aerosol particles are known and set, and the relative
humidity is indirectly controlled via the chamber's temperature. This paper
details the In-CASE setup and the dataset of 70 measurements obtained to
study the impact of the electric charges on CE. For this purpose, droplets
and particles charges are controlled through two charging systems developed
in this work – both chargers are detailed below. The droplet charge varies
from -3.0×104±1.4×103 to +9.6×104±4.3×103 elementary charges, while the particle charge ranges from zero
to -90±9 elementary charges depending on the particle radius. A
droplet radius of 48.5±1.1 µm has been considered for four
particle dry radii between 100 and 250 nm while the relative humidity level
during experiments is 95.1±0.2 %. The measurements are then
compared to theoretical models from literature – showing good agreement.
Cited by
6 articles.
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