Ice nuclei counter
From AMS Glossary
ice nuclei counter
(Abbreviated IN counter.) Any of several devices for counting atmospheric particles that serve as heterogeneous ice nuclei that are suited by composition to catalyze the formation of ice crystals in the atmosphere.
The devices operate on varied principles, include means to cool and moisturize the air within a chamber or over a nucleus-collection filter, and are intended to measure the number concentration of ice nuclei that form ice crystals as a function of temperatures that would occur in subzero tropospheric clouds (thus, 0° to near -40°C). The product is the nucleation activity temperature spectrum. Some, but by no means all, types of ice nuclei counters are designed to attempt to replicate supersaturations that occur where ice crystals form in natural tropospheric clouds.