This depends on where you are, and what is happening with air pollution levels outside and inside.
Indoor air can contains PM2.5 particles in amounts of hundreds of millions of particles per cubic metre (yes, we were amazed at this too!).
During a smoke-haze event this can easily climb to over 10 billion particles for every cubic metre of air. This is quite amazing when you know each of us breathes in about 11 m3 of air each day!
At AiRazor we believe the air you breathe should be as clean as the water you drink. You wouldn’t drink a glass of dirty water with millions of particles in it, so why breathe dirty air?