This time of year is the best time to test for radon due to the cold weather (and people keeping their windows open less).
The effect of the cold pushes radon gas into homes at higher levels than it does during summer months, making January the most accurate time to test radon gas levels.
This is true for radon testing not just in Portland, but all over the country. Learn more from these sources below.
https://www.epa.gov/radon/national-radon-action-month-information
https://www.thelunghealthinstitute.com/blog/how-national-radon-action-month-is-connected-to-copd
https://www.crcpd.org/BlankCustom.asp?page=NRAM_guide