COMMENT: From particulate to particular emission challenges

Particulate matter (PM) emitted in vehicle exhausts, especially from diesels, has long been the subject of respiratory health concerns. Since the early 1990s, with the advent of Euro I truck and bus emissions legislation, PM limits have been applied, that is to the mass of particles in relation to engine power.

But for both heavy- and light-duty diesel vehicles, the regulatory focus has now, under Euro VI and 6 legislation, extended from particulate mass to include also the number of particles, expressed as PN