We compared NASA Total Ozone Mapping Spectrometer (TOMS) overpass irradiances against ground based Brewer measurements at Ispra, Italy, and Thessaloniki, Greece, with the main objective of evaluating the effect of absorbing aerosols on TOMS UV bias using direct measurements of aerosol optical properties. Dependence of the TOMS/Brewer bias on aerosol absorption optical depth is significant. Our study demonstrates that the bias between TOMS and measured Brewer 324 nm irradiances increases with increasing aerosol absorption optical depth, τ