cut off

in aerosol sizes","in atmospheric chemistry
https://doi.org/10.1351/goldbook.C01481
The size of particles at which the retention efficiency of an instrument device drops below a specified value under defined conditions.
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2183 (https://doi.org/10.1351/pac199062112167)