Erschienen in:
Atmospheric Chemistry and Physics, 21 (2021) 9, Seite 6963-6984
Sprache:
Englisch
DOI:
10.5194/acp-21-6963-2021
ISSN:
1680-7324
Entstehung:
Anmerkungen:
Beschreibung:
Abstract. A new In-Cloud Aerosol Scavenging Experiment (In-CASE) has been developed tomeasure the collection efficiency (CE) of submicron aerosol particles bycloud droplets. Droplets fall at their terminal velocity through a1 m high chamber in a laminar flow containing aerosol particles. Atthe bottom of the In-CASE chamber, the droplet train is separated from theaerosol particles flow, and the droplets are collected in an impaction cup,whereas aerosol particles are deposited on a high-efficiencyparticulate air (HEPA) filter. The collected droplets and the filter are then analysedby fluorescence spectrometry since the aerosol particles are atomised from asodium fluorescein salt solution (C20H10Na2O5). In-CASEfully controls all the parameters which affect the CE – the droplets andaerosol particles size distributions are monodispersed, the electric chargesof droplets and aerosol particles are known and set, and the relativehumidity is indirectly controlled via the chamber's temperature. This paperdetails the In-CASE setup and the dataset of 70 measurements obtained tostudy the impact of the electric charges on CE. For this purpose, dropletsand particles charges are controlled through two charging systems developedin this work – both chargers are detailed below. The droplet charge variesfrom -3.0×104±1.4×103 to +9.6×104±4.3×103 elementary charges, while the particle charge ranges from zeroto -90±9 elementary charges depending on the particle radius. Adroplet radius of 48.5±1.1 µm has been considered for fourparticle dry radii between 100 and 250 nm while the relative humidity levelduring experiments is 95.1±0.2 %. The measurements are thencompared to theoretical models from literature – showing good agreement.