ABSTRACT
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous aromatic compounds in the environment and are also found in crude oil. PAHs are often produced as a result of combustion. Many PAHs, particularly the larger PAHs, are toxic to many species. Crude oil burns and diesel fuel burns result in PAHs downwind of the fire.
PAH concentrations in a number of burns, including test burns of crude oil and diesel fuel and at-sea burns of crude oil, are examined in this chapter. The studies included data dating 25 years ago to the present. The data were largely for the PAH concentrations in the starting oils and in the residue. In the case of some burns, the concentration of PAHs emitted as volatile compounds and adsorbed to particulate matter were available and analysed.
Crude oil burns result in PAHs downwind of the fire, mostly adsorbed to particulate matter, but the concentration on the particulate matter, both in the plume and the particulate precipitation at ground level, is often an order of magnitude less than the concentration of PAHs in the starting oil. This includes the concentration of multi-ringed (5 or 6 rings) PAHs, which are often created in other combustion processes such as low-temperature incinerators and diesel engines. There is a slight increase in the concentration of multi-ringed PAHs in the burn residue. When considering the mass balance of the burn, however, most of the PAHs are destroyed by the fire. Destruction efficiencies are typically 99.9% or greater.
Diesel fuel contains significant levels of PAHs of smaller molecular size, the 2–3-ring PAHs predominating. Burning diesel results in a greater concentration of pyrogenic PAHs of larger molecular sizes. Larger PAHs are either created or concentrated by the fire. Larger PAHs, some of which are not even detectable in diesel fuel, are found both in the soot and in the residue; however, the concentrations of these larger PAHs are low and often just above detection limits. Overall, more PAHs are destroyed by the fires than are created. As with crude oil burns, the destruction efficiencies for diesel burns are 98% or greater but are often less than those for crude oils.
