Sulfate aerosol properties derived from combining coincident ACE-FTS and SAGE III/ISS measurements

•Coincident ACE-FTS and SAGE III/ISS data combined to study sulfate aerosols.•Investigated volcanically enhanced (Raikoke and Tonga) plus background conditions.•Bimodal size distributions gave better results than monomodal.•Assuming monomodal size distribution underestimates impact on climate. Combining infrared aerosol transmittance spectra from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and visible/near infrared extinction information from coincident SAGE III/ISS measurements, the properties of stratospheric sulfate aerosols are derived under various conditions. Assuming a bimodal size log-normal distribution (rather than a monomodal one) is required to properly characterize the spectra. Analysis is performed for enhanced sulfate conditions following two recent volcanic eruptions, the Raikoke eruption in 2019 and the Hunga Tonga-Hunga Ha'apai eruption in 2022, as well as for measurements under background sulfate conditions. The traditional analysis approach of assuming a monomodal distribution likely contributes to the large uncertainties for the impact of sulfate aerosols on climate.