The Fate of PAHs Resulting from In-Situ Oil Burns

Abstract

ABSTRACT PAHs or Polyaromatic Hydrocarbons are ubiquitous in the environment and are found in crude oils. Many environmental PAHs are derived from combustion of many types including forest fires and barbeques. Some PAHs are toxic to biota and man. The concern addressed in this paper is the fate of PAHs found in crude oils when that oil is burned. Crude oil burns result in PAHs downwind of the fire, mostly adsorbed to particulate matter, but the PAH 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 % or greater. Diesel fuel contains significant levels of PAHs of smaller molecular size, the 2 to 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 the 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 typically 99 % or greater, but often less than those for crude oils. This paper will help to answer the question, are more PAHs destroyed by the fires than are created?