Investigation of aerosol particle hygroscopicity and their cloud forming potential in the supercooled temperature range
Zusammenfassung der Projektergebnisse
The hygroscopic growth of supercooled droplets grown on inorganic and organic seed particles at temperature down to minus 10°C were gained within the project. Seed particles consisting of either sodium chloride, levoglucosan, 2 dicarboxcylic acids (malonic, glutaric acid), and a tricarboxcylic acid (citric acid) were investigated. The substances were atomized from aqueous solution, resulting droplets dried and the remaining particles were size-selected applying a Differential Mobility Analyzer (DMA). The resulting monodisperse aerosol flow into a preconditioned sheath air flow at the inlet section of the laminar flow tube Leipzig Aerosol Cloud Interaction Simulator (LACIS-mobile). Depending on the set wall temperature of LACIS-mobile the particles were grown hygroscopically at temperatures down to minus 10°C. The size of the grown particles was determined applying the TROPOS in-house developed White-light Optical Particle Spectrometer (WOPS), and the effective relative humidity (RH) inside LACIS-mobile was calibrated using ammonium sulfate particles. Hygroscopicity under super-cooled conditions was determined for temperatures below 0°C up to a maximum RH of 99% and compared to values from existing Köhler models. The growth was found to be well described with the existing thermodynamic model E-AIM IV. The deviation in growth for different temperatures is small, however for the deliquescence RH of the sodium chloride particles, distinct temperature dependence was observed. In case of the supercooled organic particles no glassy phase state, and growth as model-predicted was observed. Deliquescence was not observed for the investigated organic particles.
