Effect of fuels and after-treatment of Diesel exhaust on the emission of Nitro-PAHs
Compounds in ambient air which have been implicated as being mutagenic/carcinogenic include polycyclic aromatic hydrocarbons (PAHs) and nitrated (nitro-PAHs), and more recently the nitro-oxy compounds such as 3-nitrobenzanthrone. Nitro-PAHs consist of a group of at least 200 different substances some of which are formed directly from incomplete combustion e.g. in diesel exhaust. Changes in diesel fuel, engine technology, and exhaust treatment may alter the relative concentration of nitro-PAHs on the particles, and the number and size of the particles, may alter the bioavailability, and ultimately the impact, of the nitro-PAHs. Some studies show that changes in fuel composition result in a reduction of nitro-PAHs. It is very difficult to compare the different studies available on the effect of after-treatment of diesel exhaust on nitro-PAHs and the associated mutagenicity. The results are contradictory and there is increasing evidence that volatile and semivolatile nitro-PAHs are still emitted, and that they may be increased by after-treatment processes.