Detailed characterization of the aerosol content of wildfire smoke plumes is typically performed through in situ aircraft observations, which have limited temporal and spatial coverage. Extending such observations to regional or global scales requires new remote sensing approaches, such as retrievals that make use of spectro‐polarimetric, multi‐angle imaging. In this work measurements made in a smoke plume near the town of Lebec in Southern California by the Navy Center for Interdisciplinary Remotely‐Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft on 8 July 2016 are used in conjunction with near‐coincident measurements from the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) on the National Aeronautics and Space Administration (NASA) ER‐2 high‐altitude research aircraft to assess the sensitivity of spectro‐polarimetric measurements to the black carbon content of the plume. Tracking visible features in the smoke through the sequence of AirMSPI observations allowed the height of the plume to be estimated through geometric techniques. Then, by constraining the fractional amounts of the aerosol constituents with the in situ data, radiative closure was obtained through simulations performed with a polarimetric radiative transfer code, demonstrating the ability to constrain the black carbon mass fraction to approximately 5%, given the uncertainties in the AirMSPI measurements and the assumption of external mixing of aerosol components. The AirMSPI retrieval, made using a limited set of observations from the 470 nm polarmetric spectral band alone, were also generally consistent with operational retrievals of aerosol optical depth and surface reflectance made by the Multi‐Angle Implementation of Atmospheric Correction (MAIAC) algorithm at 1 km resolution.