I alos noticed and it took some time to find out that there is a chemical container and a slidding lid on it. I didn't know what it was but removed it to clean out the dust that was in and around it. It sets under the hinged lamp and it has a slidding cover that can be removed . I couldn't move the slidding cover so I washed both parts well and then tapped the cover after adding a bit of oil to it now I can slid it open and closed. I have no use for any chemicals in there. I imagine one adds what they want then leave the slidding cover open to pull the sent through, not sure but is it ok to leave the slidding cover closed so as not to reduce suction and not to pull in dust?