Abstract One of the main limitations in state-of-the art solid-state quantum processors is qubit decoherence and relaxation due to noise from adsorbates on surfaces, impurities at interfaces, and material defects. For the field to advance towards full fault-tolerant quantum computing, a better understanding of these microscopic noise sources is therefore needed. Here, we use an ultra-high vacuum package to study the impact of vacuum loading, UV-light exposure, and ion irradiation treatments on relaxation and coherence times, as well as slow parameter fluctuations of flux tunable superconducting transmon qubits. The treatments studied do not significantly impact the relaxation rate Γ 1 and the echo decay rate $${{{\Gamma }}}_{2,{{{\rm{SS}}}^{{{\rm{e}}}$$ Γ 2 , SS e at the sweet spot, except for Ne ion bombardment which reduces Γ 1 . In contrast, flux noise parameters are improved by removing magnetic adsorbates from the chip surfaces with UV-light and NH 3 treatments. Additionally, we demonstrate that SF 6 ion bombardment can be used to adjust qubit frequencies in situ and post-fabrication without affecting qubit relaxation and coherence times at the sweet spot.