Topic
4 guides.
PM10 is every inhalable particle up to 10 micrometers; PM2.5 is the fine fraction inside it. The fine fraction is the bigger health concern, but the coarse part is the dust and pollen you can see.
PM2.5 is the particle size EPA says poses the greatest risk to health. Here are the official limits, what your monitor's number means, and what actually brings it down indoors.
EPA's answer is below 60%, ideally 30 to 50%. But mold grows where surfaces stay wet, so condensation and leaks matter as much as the room reading.
EPA's answer is 30 to 50%, never above 60%. In very cold weather, go to the low end to stop condensation. Here is the evidence and how to hit the range.
