Originally Posted by
ThermionicScott
Nothing about masks in that page.
Exactly.
Originally Posted by
erig007
PM 2.5 means particulate matter 2.5µm. The weight per cubic meter doesn't tell the whole story either. From the
EPA
Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), fine particles can lodge deeply into the lungs.
Assuming that the particulate matter is the same density (not an invalid assumption at that particle size), a 10µm particle weighs more than 2.5µm particle which weighs more than a 0.05µm particle. Roughly, you need four 2.5µm particle to weigh the same as a single 10µm particle and you need 200 0.5µm particles to weigh as much as one 10µm particle. But, because of the process by which the particulate is formed, you have many, many more 0.5µm particles than you do 10µm particles. You don't get a 30% reduction in the
number of particles that you breathe in. You might get a 30% reduction in the
weight of particles but the number is far more important. If don't breathe in one 10µm particle but you breathe in 200 0.5µm particles, you aren't doing anything to protect your health.
The guy in your other link got out the big bits but those aren't the problem.
So, yes, the mask is a placebo.