The impact of (bio-)organic substances on the ice nucleation activity of the K-feldspar microcline in aqueous solutions

Abstract. Potassium feldspars (K-feldspars), such as microcline, are considered key dust minerals inciting ice nucleation in mixed-phase clouds. Besides the high activity of recent studies also revealed a sensitivity microcline to interaction with solutes on its surface. Here, we investigate effect organic and bio-organic substances aim better understand underlying surface interactions. We performed immersion freezing experiments solutions three carboxylic acids, five amino two polyols represent these compound classes. By means differential scanning calorimeter investigated emulsified droplets suspended various solutions. Depending type solute, different effects were observed. In case acids (acetic, oxalic, citric acid), measured heterogeneous onset temperatures, Thet, showed no significant deviation from behavior predicted by water criterion, Thet(aw)=Tmelt(aw+?aw), which relates Thet melting point temperature Tmelt via constant offset ?aw. While this could be interpreted lack solute molecules surface, caused fraction heterogeneously frozen water, Fhet(aw), decrease up 40 % increasing concentrations. combination, unaltered Thet(aw) reduced Fhet(aw) suggest that active sites largely deactivated acid molecules, but amongst those remaining best highest Thet. A is acid, not only Fhet, 4 K for activities below 0.99, pointing depletion interactions citrate ions. When neutralized used instead, Fhet became even more pronounced. The slope was each solutions, found (up 10 K), significantly ?aw well reduction 60 %). Finally, polyols, criterion observed, comparison pure suspension found. Furthermore, aging 7 d, tested reversibility after d. For an ongoing irreversible degradation whereas completely reversible effects. summary, our demonstrate remarkable solutes, underscoring importance history particles source cloud atmosphere.