Hygroscopic growth and activation of HULIS particles: experimental data and a new iterative parameterization scheme for complex aerosol particles

The hygroscopic growth and activation of two HULIS (HUmic LIke Substance) and one Aerosol-Water- Extract sample, prepared from urban-type aerosol, were in- vestigated. All samples were extracted from filters, redis- solved in water and atomized for the investigations presented here. The hygroscopic growth measurements were done us- ing LACIS (Leipzig Aerosol Cloud Interaction Simulator) together with a HH-TDMA (High Humidity Tandem Dif- ferential Mobility Analyzer). Hygroscopic growth was de- termined for relative humidities (RHs) up to 99.75%. The critical diameters for activation were measured for supersat- urations between 0.2 and 1%. All three samples showed a similar hygroscopic growth behavior, and the two HULIS samples also were similar in their activation behavior, while the Aerosol-Water-Extract turned out to be more CCN ac- tive than the HULIS samples. The experimental data was used to derive parameterizations for the hygroscopic growth and activation of HULIS particles. The concept of ion (Wex et al., 2007a) and the Szyszkowski-equation (Szyszkowski, 1908; Facchini et al., 1999) were used for parameterizing the Raoult and the Kelvin (surface tension) terms of the K ¨ ohler equation, respectively. This concept proved to be very suc- cessful for the HULIS samples in the saturation range from RHs larger than 98% up to activation. It was also shown to work well with data on HULIS taken from literature. Here, different atmospheric life-times and/or different sources for the different samples showed up in different coefficients for the parameterization. However, the parameterization did not work out well for the Aerosol-Water-Extract.