http://www.nrjrealiste.fr/doc/EGR_FAP.htm
(document cited by jonule: read everything until the last line)
particulate filters (supposedly so clean according to the manufacturers) precisely allow the finest particles to pass ... some foreign studies have shown that these filters would actually release finer particles, much more dangerous for humans because, they are invisible and pass more easily in the blood. The largest particles are stopped by our biological filter (mucous membranes, hair ...).
Here is the damage they can do
found in the subject on the modified boiler (burner) by capt_maloche; it was badly placed, this is a better place to alert the people.
We could do the same with nuclear and many other harmful chemicals around us.