The Potential Contribution of Plant Materials to the Ice Nucleation Activity of Vegetated Soil Dust

A minor subset of atmospheric aerosol particles acts as so-called ice nucleating particles (INPs) to induce the freezing of supercooled droplets in tropospheric clouds, a process which often initiates the formation of precipitation. Thereby, INPs can have a strong impact on the atmospheric water cycle and the climate system, and it is of great importance to quantify their sources and abundance in the atmosphere.

Mineral, organic and biological particles have been identified as main components of atmospheric INPs. Their ice nucleation properties have been studied in numerous laboratory experiments and parameterized as a function of temperature and particle properties like chemical composition and surface area. Recently, we have identified cellulose as another potential source of atmospheric INPs, in some regions being as important as or even more important than mineral dust particles. Therefore, cellulose may also significantly contribute to the ice nucleation behavior of dust aerosols from vegetated or agricultural areas which comprise a complex and variable mixture of minerals, biological species and plant degradation compounds like cellulose.

We have used the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud simulation chamber at the Karlsruhe Institute of Technology (KIT) to investigate the ice nucleation efficiency of various cellulose types and other plant-derived species in the temperature range between -10°C and -30°C. The ice nucleation activity is expressed in terms of the temperature dependent ice-nucleation active site (INAS) density which is defined as the number density of ice nucleation active sites per aerosol particle surface area. In this contribution we will introduce the INAS concept, show the ice nucleation results for various cellulose types and other plant-derived materials in comparison to other aerosol types like minerals, and discuss atmospheric implications.