Fig. 3.

The activity concentration evolution of ${}^{222}$Rn and ${}^{218}$Po during XENON1T data-taking. In science run 0 and 1 (SR0 and SR1) the activity concentrations were stable over the entire time and we only show the initial period here. Xenon distillation campaigns to remove ${}^{222}$Rn as well as the exchange of the recirculation pumps lead to a reduction of the ${}^{222}$Rn and ${}^{218}$Po activity concentration. They gray regions indicate periods of detector calibration or maintenance