It does appear that, based on currently available data, approximately half of the entire amount of Hg associated with oil and gas (exploration, production, trans-portation, processing) enters the atmo-sphere in fuel combustion. Some unknown portion of this amount is cap-tured by pollution control equipment, but the total is likely to be less than approxi-mately 6 Mg/y (if the mean amount of Hg in crude oil is 10 ppb as expected). This would suggest that, while oil and gas account for approximately the same mass of fossil fuel burned yearly in the U.S., the amount of Hg in combusted petroleum and gas is about 10 times less than that which derives from coal (66 Mg/y).
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http://www.epa.gov/nrmrl/pubs/600r01066/600sr01066.pdfOh, what a relief. It's ten times less -- or one-tenth as much, to phrase it properly -- as the amount released by burning coal. Only about 6.6 tons/year. Hardly worth mentioning.