The relationship between surface tension and atmospheric ice-nucleating activity of agricultural soil

Ice-nucleating particles (or INP) play an important role in controlling cloud radiative properties and lifetimes. Therefore, understanding the sources and mechanisms of ice formation in clouds is vital for understanding their impact on cloud radiative feedback. Agricultural dust contributes 25% of global dust emissions and has been shown to nucleate ice at temperatures up to -6°C. This high nucleating ability of agricultural soils suggests that they may be an essential source of INPs on regional or global scales. Many organic components, which have been shown to be important for ice nucleation in soils, have surface active properties that may enhance the ice-nucleating ability of the soil. In this work, lignin was used as a reference for investigating surfactant macromolecules as a potential component of ice nucleation. Lignin solutions showed high ice-nucleating activity in line with decreases in surface tension. We contrasted our observations of lignin with observations from soil extractions from samples taken in the field. Preliminary results suggest little correlation between surface tension measurements and the ice-nucleating activity of extracted soil samples. The presence of a correlation between ice-nucleating and surface activity in soil components such as lignin, but the absence of this correlation in complete soil samples suggests that surfactants can be important ice-nucleating macromolecules, but that highly active soil samples do not necessarily reduce the surface tension at the water-air interface.