Air filter to catch radioactive particles - suggestions please

Interesting readings this morning on the filters.

The equipment room that recorded 4 microsieverts an hour was left open overnight for some repair work to be done. My apartment is just upstairs and a little to the left of this room.

Also the weather has changed, it's more humid, less windy, with the occasional very light shower.

This morning I was quite shocked to see that the reading on the HEPA-type filter had climbed from its usual 0.16 microsieverts to 0.71 microsieverts an hour, averaged over 10 minutes.

This is the highest reading I've ever recorded off the filter. I wonder if the equipment room being left open overnight has had an impact?

I'll check again tonight to note any changes as the equipment room has been shut again and shouldn't be re-opened for a few weeks.

Checked again this evening. Now down from 0.71 to 0.39 microsieverts, averaged over 10 minutes.

I really need to convince the powers-that-be to get a radon survey of the ground floor and basement done !

Crikey! Elevated levels are continuing. 0.84 microsieverts, averaged over 10 minutes. Mama mia! The highest level I've ever recorded on the filters. Even breaking yesterday's record of 0.71 microsieverts.

The weather continues to be humid, dull and cloudy, with only the very gentlest of breezes, with a light shower overnight. The externally mounted Radbox-20's readings haven't risen. It's recording a very consistent 0.14 microsieverts average.

I now have a metal oxide, volatile organic compounds (VOC) sensor placed alongside the air purifier. The air quality has been good to excellent in the same period as the elevated radiation reading on the filter.

I think I need to take another measurement in the equipment room. It was a 4 microsieverts per hour averaged reading the last time I did this. I shudder to think what it might be now

Tonight the reading has slightly declined from 0.84 to 0.68 microsieverts. This is another occasion where the morning readings are higher than those in the evening, taking into account the length of time the air purifier is actively filtering the air. The background is 0.14, the usual reading for the room the air purifier is used in, regardless of time of day.

Just out of curiosity I left the GeigerPal on a shelf made from mdf which had a visible layer of fine dust on it, and the average reading increased to 0.25 microsieverts. Again, I've not noticed this increase when I've done the same thing before. I haven't had any uranium ore, or other radioactive source uncovered in the room, so these readings would suggest that it's the air entering the room from outside which is bringing radioactive particles with it.

Just in case of equipment error, I changed the batteries and cleaned the probe using an air blower, just in case any particles were stuck on it and giving a false reading.

No change. It would appear that the HEPA-type filter is definitely trapping radioactive particles, and radioactive particles are settling with the dust on the shelf (and in my lungs )

This is an update.

Yesterday evening the reading had fallen to 0.30 microsieverts and the reading this morning was recording 0.36 microsieverts, averaged over 10 minutes. Again, morning reading higher than evening. So still above the norm, but not so much as previous days.

The weather changed too. Breezy, lowish humidity and sunny after a short, but intense rain shower, and better visibility (a clear atmosphere) after the murk of the last few days.The room air quality has been good to excellent, the majority of the time as excellent, according to my VOC sensor.

I think the events of the last few days point towards increased atmospheric radon and radon daughter nuclides, boosted on Monday by the leaving open overnight of the equipment room door, letting the suspected build up of radon accumulated there to escape into other parts of my apartment building.

Is there anyone else on the Forum regularly using an air purifier to check for increases or decreases in the amount of radiation within their living and/or working enviroment?

It would be great to compare the experience of others to my own.