Sub-2 nm meteoric smoke particles (MSPs) can act as cloud condensation nuclei in the
mesopause region of Earth at heights of 80−90km. Noctilucent clouds (NLC) in this region
have attracted much attention as a peculiar phenomenon observed only during the polar
summer. Under solar light irradiation, the absorption cross section of MSPs can be an
important parameter which determines the particle temperature and thus ice growth rate.
However, little is known about the effect of light absorption by MSPs on the NLC formation
so far. A novel experimental system is required to clarify the heterogeneous ice nucleation
process on MSPs following the light absorption.
The MICE-TRAPS apparatus at Karlsruhe Institute of Technology is used to investigate the
ice nucleation process on MSPs at mesospheric conditions by observing the mass growth rate
of nanoparticles trapped under controlled particle temperature and water vapor partial
pressure with a time-of-flight mass spectrometer . Recently, the apparatus has been
extended with an additional experimental system to irradiate the trapped nanoparticles with
488-nm laser light. This allows for the sensitive detection of radiation absorption by
measuring the mass change of water adsorbate on iron oxide or silicon oxide nanoparticles.