Black carbon microphysical measurements have revealed the unique fingerprints of pyrocumulonimbus contributions to lower stratospheric aerosol. Expanding on those findings, we have carried out high-altitude single-particle observations of refractive black carbon (rBC) aerosol at high northern latitudes (up to 81 N) in late boreal winter. The rBC measurements were obtained with a Single Particle Soot Photometer (SP2) on a NASA WB-57 high-altitude aircraft during the Stratospheric Aerosol Processes, Budget and Radiative Effects (SABRE) mission that took place in February-March 2023. Stratospheric composition is determined in part by large-scale transport patterns, such as the Brewer-Dobson circulation, in which air mainly from the tropics rises into the stratosphere and descends as it moves poleward through the middle to polar latitudes. Here, we present rBC concentrations and the microphysical state of air masses in the polar overworld-i.e., the upper stratosphere, largely isolated from direct tropospheric exchange-comprising aged downwelling mesospheric and stratospheric polar vortex air, along with non-vortex stratospheric air. Our observations clearly indicate the influence of pyrocumulonimbus, and reveal unexpectedly strong contributions at higher altitudes. Our findings offer an improved understanding of the microphysical characteristics of rBC aerosol transported to the stratosphere by pyroCb events, compared to previous interpretations derived from lower-altitude observations, and assess the climatological impact of such events on stratospheric rBC concentrations.