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

Abstract

Abstract. The hygroscopic growth and activation of two HULIS (HUmic LIke Substance) and one Aerosol-WaterExtract sample, prepared from urban-type aerosol, were investigated. All samples were extracted from filters, redissolved in water and atomized for the investigations presented here. The hygroscopic growth measurements were done using LACIS (Leipzig Aerosol Cloud Interaction Simulator) together with a HH-TDMA (High Humidity Tandem Differential Mobility Analyzer). Hygroscopic growth was determined for relative humidities (RHs) up to 99.75%. The critical diameters for activation were measured for supersaturations 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 active than the HULIS samples. The experimental data was used to derive parameterizations for the hygroscopic growth and activation of HULIS particles. The concept of ρ 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 Köhler equation, respectively. This concept proved to be very successful 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.

Hygroscopic properties of Amazonian biomass burning and European background HULIS and investigation of their effects on surface tension with two models linking H-TDMA to CCNC data

“…A detailed discussion of the SPE procedure, including column selection and performance, can be found in Varga et al (2001). In this work the ISOM fraction is hereafter referred to as HULIS, in consistency with literature (Kiss et al, 2005;Wex et al, 2007;Ziese et al, 2008). The extraction procedure of the HULIS was identical for the SMOCC and K-puszta samples.…”

“…(11), the critical supersaturation can now be calculated and the parameters a and b , which define the surface tension of the sample, are adjusted until the results of the modelled critical supersaturation from the H-TDMA data match the CCNC data. These parameters are now used to calculate a new ρ ion and the iteration continues until the solution has converged (Ziese et al, 2008). The main advantage of this approach is that one obtains a concentration dependent surface tension function as an output, which is consistent with the Szyszkowski-Langmuir equation.…”

“…The second model used in this study was first introduced by Ziese et al (2008) for a similar HULIS sample set. It is also based on Köhler theory, but without taking into account the non-ideality of the solute.…”

“…All model parameterizations rely on an assumption of the value of the surface tension as a function of surfactant concentration. In this work, we used two single parameter models: κ R introduced by Rissler et al (2004), also described in Vestin et al (2007), and ρ ion from Ziese et al (2008). Both are based on the Köhler equation…”

“…They have produced quite diverse results due to the vast number of species that can fall under the HULIS definition; since HULIS is ultimately defined by the separation method used in the isolation procedure of the sample. Gysel et al (2004), Dinar et al (2006), Wex et al (2007) and Ziese et al (2008) all determined the hygroscopic properties of isolated HULIS samples, measuring hygroscopic growth factors between 1.05 and 1.24 at 90% RH.…”