Direct observations of aerosol infrared (IR) radiative forcing are rare and almost nonexistent. We determine the aerosol radiative forcing in the mid-IR window using cruise data obtained from the NOAA Ship R. H. Brown during ACE-Asia. The analysis is based on FTIR spectra measured by the Maritime Atmospheric Emitted Radiance Interferometer (M-AERI). These data enable surveying the range of instantaneous IR forcings caused by the variety of aerosol types and column loadings encountered during the cruise. We show that the IR surface forcing can be significant for natural as well as anthropogenic aerosols, with values in both cases reaching almost 10 Wm^-2. Factors that govern the underlying physics will be described. To the best of our knowledge this is, to date, the most comprehensive observational determination of aerosol IR radiative forcing.