Originally Posted by
fietsbob
Particle filter masks for those who must share the roads with diesel busses , like Central London, have been made for a long time..
And totally ineffective. An N95 particulate filter will filter out 95% of particulates above 0.3µm. The bulk of particulates from diesel exhaust falls into a range from 0.01µm to 0.05µm. Far below the ability of the filter mask. You could go to a full respirator and get better protection but the smaller the range the mask filters, the harder it is to get air through the filter. Masks...even the N95s...aren't really meant for exercise.
Originally Posted by
erig007
The problem with both of these articles is that he doesn't give the range of particulate that is being filtered. A screen door can have a 99% filtration rate if the particles being filtered are 20mm wide. If the particles are 2mm wide, the screen door becomes less effective and if the particles are 0.2mm wide, the efficiency of filtration is zero.
This is the case of the masks in this "test". The bulk of the particulate being filtered is below the range of the filter so the "efficiency" for sub 0.3µ particles is effectively zero.
Even worse, these filters have absolutely no effect on the permanent gases that could actually harm a human. They don't filter CO, NOX, unburned hydrocarbons or even sulfuric acid droplets (which can happen with high sulfur fuels). Thankfully, those gases aren't really much of a problem in the US, Canada or Europe since our vehicles have to have devices to reduce all those materials.