R. Ullrich

A New Ice Nucleation Active Site Parameterization for Desert Dust and Soot

AbstractBased on results of 11 yr of heterogeneous ice nucleation experiments at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber in Karlsruhe, Germany, a new empirical parameterization framework for heterogeneous ice nucleation was developed. The framework currently includes desert dust and soot aerosol and quantifies the ice nucleation efficiency in terms of the ice nucleation active surface site (INAS) approach.The immersion freezing INAS densities nS of all desert dust experiments follow an exponential fit as a function of temperature, well in agreement with an earlier analysis of AIDA experiments. The deposition nucleation nS isolines for desert dust follow u-shaped curves in the ice saturation ratio–temperature (Si–T) diagram at temperatures below about 240 K. The negative slope of these isolines toward lower temperatures may be explained by classical nucleation theory (CNT), whereas the behavior toward higher temperatures may be caused by a pore condensation and freezing mechan...

Ice nucleation activity of agricultural soil dust aerosols from Mongolia, Argentina, and Germany

Soil dust particles emitted from agricultural areas contain considerable mass fractions of organic material. Also, soil dust particles may act as carriers for potentially ice-active biological particles. In this work, we present ice nucleation experiments conducted in the AIDA cloud chamber. We investigated the ice nucleation efficiency of four types of soil dust from different regions of the world. The results are expressed as ice nucleation active surface site (INAS) densities and presented for the immersion freezing and the deposition nucleation mode. For immersion freezing occurring at 254 K, samples from Argentina, China and Germany show ice nucleation efficiencies which are by a factor 10 higher than desert dusts. On average, the difference in ice nucleation efficiencies between agricultural and desert dusts becomes significantly smaller at temperatures below 247 K. In the deposition mode the soil dusts showed higher ice nucleation activity than Arizona Test Dust over a temperature range between 232 and 248 K, and humidities RHice up to 125%. INAS densities varied between 109 and 1011 m-2 for these thermodynamic conditions. For one soil dust sample (Argentinian Soil), the effect of treatments with heat was investigated. Heat treatments (383 K) did not affect the ice nucleation efficiency observed at 249 K. This finding presumably excludes proteinaceous ice nucleating entities as the only source of the increased ice nucleation efficiency.

Mineralogy and mixing state of North African mineral dust by on-line single-particle mass spectrometry

Marsden et al. use laser desorption/ionization single-particle mass spectrometry to analyze source mineral dust particles, and ambient dust-laden aerosol sampled in North Africa. They apply their recently developed mass spectral analysis method to distinguish between different silicate minerals, based on the time delay that the relevant ions are detected in the MS. This time delay relates to the crystal structure of the different mineral phases. Distinguishing between different specific mineral phases or families in individual particles is a serious analytical challenge. The results presented here are quite novel, despite the various issues related to the semi-quantitative nature of the analysis, only being able to identify or distinguish some of the major mineral phases, and not achieving complete separation between different phases (the spread in the