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Show and many, if not most, must be presumed to be present in residual quantities in the flue gas, albeit some in concentrations so small that they may never be measured. In terms of quantity, formaldehyde, not only a carcinogen but also a potent precursor to the formation of atmospheric ozone, is an abundant byproduct of combustion in petroleum industry heaters and boilers exceeding, for example, 10 tons per year at a typical 250,000 bpd transportation fuels refinery. By comparison, the total emission of the polycyclic aromatic hydrocarbons amounts to only about 1/2 ton per year; nevertheless, at one particular location near the refinery, the total lifetime excess cancer risk to the most exposed individual exceeds one in a million and is dominated by benzo(a)pyrene (28%), indeno(U3-cd)pyrene (23%), benzo(b)fluoranthene (11%), benz(a)anthracene (9%), benzo(k)fl uoranthene (6%), other combustion toxics (4%), and fugitive emissions (19%).8 C O M B U S T I O N AIR TOXIC EMISSIONS [to be regulated under CAA112(a)(1)] Typical 250,000 bpd Refinery ^ « s ^ H .onnawehyde ^ ^ w P § ^ \ 1 toluene flfllli iSS •j lillliPf E3 benzene ^ fc^^^' • anth, prop, phen, acel 45% 30% 10% 5% 5% 3% 2% COMPONENTS OF EXCESS CANCER RISK [to be regulated under CAA 112(f)(2)(A)] Typical 250,000 bpd Refinery E3 benzo(a)pyrene 28% • m<Jeno(1.2.3-od)pyrene 2 3 % 0 benzo(b)fluoranthene 1 1 % • benz(a)anthracene 9% • benzo(k)fluoranthene 6% • other combustion toxics 4 % E 3 fugitive emissions 19% Pooled source testing on petroleum industry heaters and boilers in the Los Angeles basin has suggested that the most abundant P A H species are anthracene, benzo(a)pyrene, dibenz(a,h)anthracene, fluoranthene, fluorene, indeno(lJ23-cd)pyrene, naphthalene, phenanthrene, and pyrene. A somewhat disturbing suggestion also has emerged; viz., "It is clear from these data that process heaters with low N O x burners seem to exhibit a wider distribution of many P A H species, in addition to a higher level of emissions of total PAHs." 9 While not all data support that contention, the observation that at least some approaches to low N O x combustion are, in fact, approaches to unmixedness lends some credence to that idea, at least in the case of the partially oxygenated carcinogens like formaldehyde and acetaldehyde. That is but one example of the confusion currently arising out of the fact that reliable measurements of trace combustion toxics are technically challenging, time-consuming and expensive, in consequence of which most field studies measure only a handful of toxics at very restricted fuel compositions and combustion conditions. Indeed, it is becoming more and more apparent that "... there is a need to understand the influence of combustion process parameters on emissions ..." 10 that 2 I-3 |