Long-term variations in the SO₂ volume mixing ratio measured at the cloud top between 1978 and 2025. The data prior to 2012 are taken from Esposito et al. 1984 (Pioneer Venus) and from Marcq et al. 2020 (Venus Express). They have been obtained in the UV, at an altitude of about 70 km, and the TEXES data have been normalized accordingly. The solar activity (measured by the sunspot number) is shown for comparison.