cold trap

noun2

1. •
   In vacuum applications, a device that condenses all vapours except the permanent gases into a liquid or solid, typically to prevent contamination of a vacuum pump.
2. •
   An atmospheric layer that is significantly colder than the adjacent layers both deeper and higher. It keeps ascending gases that have high melting points from escaping the atmosphere by freezing them to a solid which then drops back to the planet surface.

   • The impact of a large body in the oceans would inject large quantities of water through the tropopause cold trap into the stratosphere and lower mesosphere. — 1983