Air Pressure Effects on Radon Readings

The units are located in a basement.

The pink line is air pressure, the blue line is the detector reading in CPM. The detector reading is the average reading for one hour.

There appears to be some correlation between the two, in that increases in pressure cause increases in radon readings - although the results are opposite to what I would first expect, which would be that a decrease in pressure would cause an increase in the reading, due to more outgassing from the ground. One thought is that an increase in air pressure "bottles up" the radon in the basement, while a decrease in pressure allows it to escape to the outside.

Also very interesting are the large peaks that occur once a day, in the 10 AM to Noon local time range. I do not believe there is a correlation between this peak and activity in the room where the experiement is taking place. Nor any change to the HVAC system at this time of the day. And as it is in a basement room, the temperature is fairly constant during the day. (No windows in the room) There is a small bump in the air pressure reading at this time of the day, so it may be due to a daily increase in the pressure at high noon. One idea from a read is that air in the attic is heated, creating a chimney effect and sucking air through the house, pulling more radon into the basement.

This is an ongoing experiment, perhaps more data will shed some light on the data. Comments appreciated!