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 diesel, residue, and soot samples collected during each burn were quantitatively characterized by GC/MS. A simple model based on mass balance of individual petroleum PAHs pre-and postburn was proposed to estimate the destruction efficiencies of the total petroleum PAHs. This study demonstrates the following: (1) Distributions of PAHs in the original diesel and soot were very different. (2) The average destruction efficiencies for the total target diesel PAHs including five alkylated PAH series and other EPA priority unsubstituted PAHs were greater than 99%. (3) Using the model, 27.3 kg of the diesel PAHs were destroyed for each 1000 kg of diesel burned. These were mostly two-and three-ring PAHs and their alkylated homologues. (4) Combustion also generated trace amounts of high molecular weight fiveand six-ring PAHs as well as the four-ring benz[a]anthracene. But the total mass of these pyrogenic PAHs was found to be extremely low: only 0.016, 0.032, and 0.048 kg 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, we conclude that in situ burning is an effective measure to minimize the impact of an oil spill on the environment, greatly reducing exposure of ecosystems to the PAHs of spilled oils. A new "pyrogenic index", Σ(other three-to six-ring PAHs)/Σ(five alkylated PAHs), is proposed (see the text for the definition) as a quantitative indicator for identification of pyrogenic PAHs and for differentiating pyrogenic and petrogenic PAHs. Also, this index is demonstrated to be a useful tool for distinguishing heavy fuels from crude oils and light refined products. This method, combined with other criteria, is expected to be applicable to such situations as oil spill investigations, site assessment, and apportioning of legal responsibility for pollution cleanup.

A group of 25 agencies from Canada and the United States conducted a major offshore burn experiment near Newfoundland, Canada. Two lots of oil, about 50 cubic meters (50 tons) each, were released into a fireproof boom. Each burn lasted over an hour and was monitored for emissions and physical parameters. Over 200 sensors or samplers were employed to yield data on over 2000 parameters or substances. The operation was extensive; more than 20 vessels, 7 aircraft and 230 people were involved in the operation at sea. The quantitative analytical data show that the emissions from this in-situ oil fire were less than expected. All compounds and parameters measured more than about 150 meters from the fire were below occupational health exposure levels; very little was detected beyond 500 meters. Pollutants were found to be at lower values in the Newfoundland offshore burn than they were in previous pan tests. Polyaromatic hydrocarbons (PAHs) were found to be lower in the soot than in the starting oil and were consumed by the fire to a large degree. Particulates in the air were measured by several means and found to be of concern only up to 150 meters downwind at sea level. Combustion gases including carbon dioxide, sulphur dioxide, and carbon monoxide did not reach levels of concern. Volatile organic compounds (VOCs) were abundant, however their concentrations were less than emitted from the nonburning spill. Over 50 compounds were quantified, several at levels of concern up to 150 meters downwind. Water under the burns was analyzed; no compounds of concern could be found at the detection level of the methods employed. Toxicity tests performed on this water did not show any adverse effect. The burn residue was analyzed for the same compounds as the air samples. Overall, indications from these burn trials are that 150 meters or farther from the burn source emissions from in-situ burning are lower than health criteria levels.

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A series of mesoscale burns were conducted in 1998 to assess fire-resistant booms, twelve of these were used to study emissions from diesel oil burns. Extensive sampling and monitoring were conducted to determine the emissions at nine downwind ground stations, one upwind ground station, and at six side stations. Particulates were measured using high-volume samplers and real-time particulate analyzers. Particulate samples in air were taken and analyzed for polycyclic aromatic hydrocarbons (PAHs). Water under the burns was analyzed; small amounts of PAHs were found. The burn residue was analyzed for PAHs as well. PAHs were at about the same concentration in the residue than in the starting oil, however, there is a slight differential concentration increase in some higher molecular weight species in the residue. Combustion gases including carbon dioxide, sulphuric acid aerosols, and sulphur dioxide were very low and in some cases undetectable. Volatile organic compound (VOC) emissions were measured in Summa canisters. Over 100 compounds were identified and quantified; most concentrations were too low to be considered a health risk. It was concluded that small burns of this size (burn area about 25 m2) are too small to pose a health hazard.

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