Originally Posted by
cyccommute
You seem to be missing my point. Dust masks filter the large bits, which is good, but they don't work on the smaller particles. Weight-wise, most of the particulate is in the 10µm range. But with regard to the number of particles, which is the more important number, there are few particles in the 10µm range. The vast majority of particulates is in the 0.05µm range and lower. The masks filter out the big bits but there aren't very many of them. The masks are ineffective against the smaller particles. The masks are a placebo at best.
wolfchild has a very valid point.
Seems it isn't just a placebo for WHO
WHO | Ambient (outdoor) air quality and health
"WHO Air Quality Guidelines" estimate that reducing annual average particulate matter (PM10) concentrations from levels of 70 μg/m3, common in many developing cities, to the WHO guideline level of 20 μg/m3, could reduce air pollution-related deaths by around 15%.
And since those masks are tested against PM2,5 my guess would be about 30-50% reduction of air pollution-related deaths.