One particular issue to take on. This site is currently powered out of Germany where lung cancer is the 3rd most frequent form of cancer. Of course, Germany is still a place with a large number of smokers. As it turns out though, a good fraction of the lung cancer cases are officially attributed to the presence of radon in the air. And this holds even more so for smokers.
Radon itself is mostly just a mediator.
There are several isotopes of radon which are of interest but the information here pertains to 222Rn, a decay product of uranium. Uranium is present in the ground everywhere on earth in varying concentrations and poses no problem, as it remains down there. Unfortunately, it will decay into other elements and eventually turn into radon. Radon is a nobel gas and as such will move around easily and may exit from the ground.
The graph gives the rate of detecting two of the decay daughters of 222Rn, which are pollonium isotopes 218Po and 214Po, over the course of 5 month. More details about the measurement, which was performed in the bedroom of a second floor appartment close to the center of München, will follow. A large variation in the relative rate is apparent and the factors driving those changes are not trivial to identify.
Radon 222Rn is part of the Uranium Series decay chain. The here relevant section of the decay chain looks like this (more details can be found on Wikipedia).