Quantitative characterization of PAHs in burn residue and soot samples anddifferentiation of pyrogenic PAHs from petrogenic PAHs - The 1994 Mobile Burn Study

Several mesoscale burns were conducted in 1994 in Mobile Bay, AL, to study various aspects of diesel fuel burning in situ. The target PAHs in the dies el, residue, and soot samples collected during each burn were quantitativel y characterized by GC/MS. A simple model based on mass balance of individua l petroleum PAHs pre- and postburn was proposed to estimate the destruction efficiencies of the total petroleum PAHs. This study demonstrates the foll owing: (1) Distributions of PAHs in the original diesel and soot were very different. (2) The average destruction efficiencies for the total target di esel PAHs including five alkylated PAH series and other EPA priority unsubs tituted PAHs were greater than 99%. (3) Using the model, 27.3 kg of the die sel PAHs were destroyed for each 1000 kg of diesel burned. These were mostl y two- and three-ring PAHs and their alkylated homologues. (4) Combustion a lso generated trace amounts of high molecular weighs five- and six-ring PAH s as well as the four-ring benz[a]anthracene. But the total mass of these p yrogenic PAHs was found to be extremely low: only 0.016, 0.032, and 0.048 k g of the five- and six-ring PAHs were generated by combustion in the three different scenarios for each 1000 kg of diesel burned. From these points, w e conclude that in situ burning is an effective measure to minimize the imp act of an oil spill on the environment, greatly reducing exposure of ecosys tems to the PAHs of spilled oils. A new "pyrogenic index", Sigma(other thre e- to six-ring PAHs)Sigma(five alkylated PAHs), is proposed (see the text f or the definition) as a quantitative indicator for identification of pyroge nic PAHs and for differentiating pyrogenic and petrogenic PAHs. Also, this index is demonstrated to be a useful tool for distinguishing heavy fuels fr om crude oils and light refined products. This method, combined with other criteria, is expected to be applicable to such situations as oil spill inve stigations, site assessment; end apportioning of legal responsibility for p ollution cleanup.