FELD 02/2017

DUST EMISSIONS DUST

DUST EMISSIONS DUST EMISSIONS This dust sample from northern China contains a mix of bare, rounded particles from the Gobi desert and loess soil particles from adjacent grass steppes of Inner Mongolia. — 100 µm However, the largest known source of these »ice nuclei« is desert dust, of which about 1.5 billion tonnes are released into the atmosphere every year. »Soil dust from farmland is also suspected of having a major influence on cloud formation,« says Funk. This phenomenon has now for the first time been explored in more detail with colleagues from the Karlsruhe Institute of Technology (KIT). For this purpose, experiments were carried out at the KIT in a cloud chamber where the processes of cloud formation can be simulated. »These experiments focused on the ice nuclei forming properties of four different types of dust,« explains Funk. The soil samples from northern Germany, Mongolia and Argentina come from ZALF’s dust archive. The results of the experiment are astonishing: The cloud formation activity of agricultural dust is about ten times higher than that of desert dust. »These facts are impressive, although we do not yet know the underlying mechanisms,« Funk sums up. This will be the task of further joint research in order to better understand the diverse interactions between soil surface and atmosphere. »Dusts are still largely unknown, and relatively little research has been done so far. That‘s exactly what makes them so exciting for us,« says the dust hunter. NO DUST, NO PRECIPITATION However, the consequences of dust emissions are not limited to the regional level, instead, they have a global impact on the climate and environment. »Storms carry the dust high into the air, where it sometimes travels thousands of kilometres to distant places and sometimes even around the globe,« Funk adds. Desert storms blow the dust particles from the Sahara in Africa across the Atlantic Ocean to Central and South America. Particles that land in the ocean carry iron and silicon into the water. The nutrients lead to increased algae formation rates – an additional food source for fish. But a strong growth of algae also clouds the water and thus endangers coral reefs in the Caribbean. But dust has an even more important role to play in the atmosphere because here it is a vital precondition for clouds to form. In order for rising water particles to form clouds, they must condense or freeze, but evaporated water has a freezing point of -70°C as it is completely sterile and clean. A small trick from nature ensures that the water molecules in the atmosphere freeze at much more moderate temperatures. So-called »ice nuclei« serve as jump starters. These are small dirt particles, such as pollen or soot particles, volcanic dust or sea salt particles on which ice crystals grow. DR. ROGER FUNK The cloud formation activity of agricultural dust is about ten times higher than that of desert dust. is head of the working group on wind erosion at the Institute for Soil Landscape Research at ZALF. After studying agriculture and rural development at the Humboldt Universität zu Berlin, he received his doctorate at the Technische Universität Berlin. DR. ROGER FUNK www.zalf.de/feld/en 08 09