Having a comprehensive understanding of the stratospheric aerosol layer is critical for calculating the global radiation budget, stratospheric dynamics and ozone layer recovery. The size distribution determines the radiative and chemical properties of the aerosol layer. Characterizing the background conditions of the stratospheric aerosol size distribution is necessary for having a stable baseline to compare to when identifying the impact and magnitude of stratospheric perturbations. Understanding natural variations in the aerosol size distribution following perturbations is important for accurately modelling the climate and ozone impacts of these perturbations. A better understanding of the formation, evolution, and perturbation of stratospheric aerosol will help inform decisions regarding potential climate mitigation strategies. Within the NOAA Earth’s Radiative Budget Initiative, the Baseline Balloon Stratospheric Aerosol Profiles (B2SAP) project aims to characterize the global stratospheric aerosol number and size distribution using a latitudinally distributed network of balloon sonde sites. At present there are four regular B2SAP launch sites: i) Boulder, CO, USA, (40oN), ii) Lauder, NZ, (45oS), iii) Hilo, HI, USA, (20oN), and iv) Reunion Island, FR, (20oS). B2SAP produces vertical profiles from the surface to 28 km of meteorological data, ozone and water vapor as well as size distribution and number concentration. The effective radius of aerosol is also derived, easing comparison with models and other sensors, such as SAGE-III/ISS. Certain events, such as volcanic activity or large biomass burning can perturb the size distribution of stratospheric aerosol. Here, we use a combination of B2SAP and model data to investigate the impacts various past events have had on the effective radius of the stratospheric aerosol layer.