Can't help but wonder if this is slightly similar to a problem with condensing humidity in some Air Force electronics.
Is it possible that you could reduce the "habitat" for the PM by keeping temperatures higher ?
When does PM multiply ?
Only had bad PM once in about 20 years. Don't remember what I did - except a whole bunch of cleaning.
The Nice Part about Running a Temperature ~
A 30 Degree day feels like a 40 Degree Day