Global and systematic stratospheric aerosol number and size distributions from the NOAA Balloon Baseline Stratospheric Aerosol Profiles (B2SAP) project

Abstract. Stratospheric aerosol plays critical roles in the global radiative balance and stratospheric chemistry. A robust evaluation of stratospheric aerosol abundance and size distributions over time is required to determine and accurately model aerosol impacts on the Earth system. The Balloon Baseline Stratospheric Aerosol Profiles (B²SAP) project uses weather balloons to collect regular vertical profiles of stratospheric aerosol number and size distributions, at eight latitudinally diverse locations across the globe from the ground to ~30 km altitude. These systematic in situ measurements allow the micro-physical properties of the background stratospheric aerosol and their variability to be examined. These on-going measurements provide constraints for aerosol modules of large coupled models and reference for satellite retrievals relying on previous size distribution assumptions. The lightweight, low-powered Portable Optical Particle Spectrometer (POPS) instrument is deployed on balloon platforms, allowing for high vertical resolution and the detection of stratospheric aerosol down to 140 nm diameter. This paper presents the B²SAP aerosol dataset (DOI: https://doi.org/10.25921/mchy-y552, Smith et al., 2026), including a description of the B²SAP network, POPS measurement principles, sensitivity analysis, calibration procedures, file processing workflow and a comparison with aerosol extinction from the GloSSAC product.