In the atmosphere, aerosol particles can grow hygroscopically as well as serve as cloud condensation nuclei (CCN) depending on their chemical composition and size. They are therefore crucial for the generation of clouds.

The hygroscopic growth and droplet activation of different kinds of aerosol particles has been examined in several studies utilizing the Leipzig Aerosol Cloud Interaction Simulator (LACIS). LACIS allows to measure both, hygroscopic growth up to very high relative humidity (RH > 99%), and droplet activation under laminar flow conditions. The goal of the investigations was to examine the connection between hygroscopic growth and droplet activation and to test to which extent these two processes can be described, e.g. using the Köhler theory.

Relevant achievements and results comprise the consistent descriptions of both hygroscopic growth and droplet activation for different sea water (without and with organic material (algal exudate); Niedermeier et al., 2008, Wex et al., 2010) and atmospheric HULIS (HUmic Like Substances) samples (Wex et al., 2007a, Ziese et al., 2008, Kristensen et al, 2012), as well as secondary organic aerosol (SOA; Wex et al., 2009, Petters et al., 2009), and coated and uncoated soot particles (Henning et al., 2010, Snider et al., 2010, Stratmann et al., 2010). For the first time the in-situ behavior of slightly soluble particle deliquescence (RH approx 99%) could be observed and quantified (Wex et al., 2007b). Furthermore, the mass accommodation coefficient of water vapor on liquid water was determined. It was found to be between 0.3 and 1 (Voigtländer et al., 2007).

However, all of these investigations were carried out assuming average and/or slowly changing thermodynamic conditions in the vicinity of the particle/droplet. That means possible influences of turbulent temperature and water vapor fluctuations and consequently saturation fluctuations on the hygroscopic growth and activation behavior were not investigated. With the turbulent moist air wind tunnel LACIS-T (turbulent Leipzig Aerosol Cloud Interaction Simulator) we aim at hygroscopic growth and activation studies under turbulent conditions. First results on the influence of turbulence on cloud drop activation will be submitted soon.

Literature:

Henning et al. (2010), Soluble mass, hygroscopic growth and droplet activation of coated soot particles during LExNo, J. Geophys. Res., 115(D11206), doi:10.1029/2009JD012626.

Kristensen et al. (2012), Hygroscopic growth and CCN activity of HULIS from different environments, J. Geophys. Res., 117(22), doi:10.1029/2012JD018249.

Niedermeier et al. (2008), LACIS-measurements and parameterization of sea-salt particle hygroscopic growth and activation, Atmos. Chem. Phys., 8, 579–590.

Petters et al. (2009), Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol - Part 2: Theoretical approaches, Atmos. Chem. Phys., 9, 3999-4009.

Snider et al. (2010), Intercomparison of CCN and hygroscopic fraction measurements: Coated-soot particles investigated during LExNo, J. Geophys. Res., 115(D11205), doi:10.1029/2009JD012618.

Stratmann et al. (2010), Examination of laboratory-generated coated soot particles: An overview over the LExNo campaign, J. Geophys. Res., 115(D11203), doi:10.1029/2009JD012628.

Voigtländer et al. (2007), Mass accommodation coefficient of water: a combined computational fluid dynamics and experimental data analysis, J. Geophys. Res., 112(D20208), doi:10.1029/2007JD008604.

Wex et al. (2007a), Hygroscopic growth and measured and modeled critical super-saturations of an atmospheric HULIS sample, Geophys. Res. Lett., 34(L02818), doi:10.1029/2006GL028260.

Wex et al. (2007b), Deliquescence and hygroscopic growth of succinic acid particles measured with LACIS, Geophys. Res. Lett., 34(L17810), doi:10.1029/ 2007GL030185.

Wex et al. (2009), Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol: Part 1 - Evidence from measurements, Atmos. Chem. Phys., 9, 3987-3997.

Wex et al. (2010), The influence of algal exudate on the hygroscopicity of sea spray particles, Advances in Meteorology, 2010, 365131, doi:10.1155/2010/365131.

Ziese et al. (2008), Hygroscopic growth and activation of HULIS particles: experimental data and a new iterative parameterization scheme for complex aerosol particles, Atmos. Chem. Phys., 8, 1855-1866.