These nuclei include particles of ammonium sulfate and magnesium sulfate. Other condensation nuclei include tiny particles of dust and particles from smoke. Scientists are not sure whether particles of salt from ocean spray can also act as condensation nuclei. Instead, the water vapor turns directly to ice through a process called sublimation. A freezing nucleus is a small particle that is similar to a cloud condensation nucleus.
Most freezing nuclei are dust or tiny specks of plant debris raised by the wind.
Freezing nuclei are sometimes called ice nuclei. Drops and snow crystals fall when they grow too heavy to be held up by the air. Droplets grow into raindrops through the condensation of additional water vapor onto their surfaces and by combining with smaller droplets. A snow crystal can become heavy enough to fall by growing as water vapor sublimates onto it. In some cases, this water vapor comes from evaporating cloud droplets.