The IASI satellite sensor is used to document the variability and evolution of tropospheric ozone (O₃). IASI O3 retrievals generally use a single a priori profile which can be responsible for biases and too-low variability. We have therefore implemented a dynamical a priori profile based on pixel location, month and tropopause height. Comparison with 10 years of global ozonesonde profiles shows large improvements in the retrieved tropospheric O₃, with biases corrected and enhanced variabilities.