When Molekule begins the purification process, it performs an initial cleanup of your room based on the preferences you select. This cycle provides an initial air replacement, filling your room with purified air. Molekule will then switch to maintaining and retaining the cleanliness level of your indoor air.
You can change the mode from the home screen by selecting the maintenance cycle to run on any of the modes - Silent, Auto, or Boost. You can learn more about the modes here.