Understanding the air indoors
Indoor air is described by a small set of numbers that are easy to quote and easy to misread. Particulate concentration, air change rate and filter efficiency each answer a different question, and none of them substitutes for another. This site explains what each measurement covers, where it comes from, and what it does not tell you.
Measurement, not marketing
A figure printed on a box is a laboratory result obtained under stated conditions. Room volume, furnishing, occupancy and air movement all shift what happens in practice. Reference material here describes the test conditions behind each number so the gap between the specification and the room is visible.
Three numbers worth separating
PM2.5 reports the mass of fine particulate suspended in a cubic metre of air. Air changes per hour describes how often a room's volume is replaced. MERV rates how efficiently a filter captures particles in defined size bands. A high rating in one says nothing about the other two.