Wolkenkernen

Cloud condensation nuclei (CCN), known in German as Wolkenkernen, are aerosol particles on which water vapor condenses to form cloud droplets. They range in size roughly from 0.01 to 1 micrometer in diameter and can include sea spray salts, mineral dust, sulfates, organic matter, and soot. Activation of CCN into cloud droplets requires supersaturation of water vapor in rising air, and depends on the particle's size, composition, and hygroscopicity.

Particles that are highly hygroscopic—such as sea salt and hydrated sulfates—activate at lower supersaturations, whereas less hygroscopic particles require stronger supersaturation. The result is a distribution of activated droplets that shapes the droplet spectrum of a cloud.

CCN concentrations influence cloud properties. More CCN lead to more numerous, smaller droplets, increasing the cloud's albedo (the Twomey effect) and potentially altering cloud lifetime and precipitation efficiency. The net climate effect of CCN is complex and a major source of uncertainty in climate models.

Sources include natural processes (marine aerosol, dust, volcanic ash, biogenic emissions) and human activities (fossil fuel combustion, biomass burning, industrial processes). Some particles form secondarily from gas-phase precursors, expanding the CCN population.

Measurement involves CCN counters and in-situ cloud data, with satellite observations providing broader context. Researchers use aerosol and climate models to simulate CCN impacts on cloud formation and climate forcing.