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March 30, 2016
A cornerstone of U.S. environmental policy has been the reduction of harmful tailpipe emissions from cars and trucks. Thanks to EPA regulations of mobile sources, air pollutants have been reduced by millions of tons in the urban environment. Several EPA fuel regulations have concerned octane. Octane is a gasoline additive that is needed for the proper functioning of modern engines. Octane sources have taken many forms throughout the years, both renewable and petroleum-based. They include lead, methyl tertiary butyl ether (MTBE), benzene, toluene, ethyl-benzene and xylene (BTEX), and ethanol (a biofuel). As adverse health and environmental consequences have been discovered for lead and petroleum-based octane providers, they have been removed from the fuel supply or decreased. Today, there are two primary sources of octane used in the U.S. gasoline supply, the BTEX complex (a petroleum refining product commonly referred to as gasoline aromatics), and ethanol.
The octane rating is a measure of a fuel’s ability to avoid knock. Knock occurs when fuel is prematurely ignited in the engine’s cylinder, which degrades efficiency and can be damaging to the engine. Knock is virtually unknown to modern drivers. This is primarily because fuels contain an oxygenate that prevents knock by adding oxygen to the fuel. This oxygenate is commonly referred to as octane.
At most retail gasoline stations, three octane grades are offered, 87 (regular), 89 (mid-grade), and 91-93 (premium). The higher the octane number, the more resistant the gasoline mixture is to knock. The use of higher octane fuels also enables higher compression ratios, turbocharging, and downsizing/downspeeding—all of which enable greater engine efficiencies and higher performance. Currently, high-octane fuel is marketed as ‘premium,’ but automotive manufacturers have expressed interest in raising the minimum octane pool in the United States to enable smaller, more efficient engines. Doing so would increase vehicle efficiency and lower greenhouse gases through decreased petroleum consumption.
In the early 20th century, automotive manufacturers were searching for a chemical that would reduce engine knock. In 1921, automotive engineers working for General Motors discovered that tetraethyl lead (better known as lead) provided octane to gasoline, preventing engine knock. While aromatic hydrocarbons (such as benzene) and alcohols (such as ethanol) were also known octane providers at the time, lead was the preferred choice due to its lower production cost. Leaded gasoline was the predominant fuel type in the United States until the U.S. Environmental Protection Agency (EPA) began phasing it out in the mid-1970s because of proven serious health impacts.
Early in its use as a fuel additive, health concerns were raised regarding the use of lead in gasoline. In 1924, 15 refinery workers in New Jersey and Ohio died of suspected lead poisoning. As a result, the Surgeon General temporarily suspended the production of leaded gasoline and convened a panel to investigate the potential dangers of lead use in gasoline. While the panel found insufficient evidence of lead poisoning over a short time period, the panel warned that longer exposure to lead could result in “chronic degenerative diseases of a less obvious character.”
Despite these warnings, the Surgeon General set a voluntary standard of lead content, which the refining industry successfully met for decades. It was not until the 1960s, following extensive health research, that the devastating health impacts of low-level lead exposure were established. Children’s developing bodies are particularly sensitive to low-level, ambient exposures to lead. The health impacts of lead exposure in children include anemia, behavioral disorders, low IQ, reading and learning disabilities, and nerve damage. In adults, lead exposure is associated with hypertension and cardiovascular disease. Prior to the lead phase-out in gasoline, the total amount of lead used in gasoline was over 200,000 tons per year.
Congress passed the Clean Air Act in 1970, setting in motion the formation of the EPA and, ultimately, the removal of lead from gasoline. EPA estimates that between 1927 and 1987, 68 million children were exposed to toxic levels of lead from leaded gasoline alone. The phase-out of lead from gasoline subsequently reduced the number of children with toxic levels of lead in their blood by 2 million individuals a year between 1970 and 1987.
1970: Congress passes the Clean Air Act. The EPA is formed and given the authority to regulate compounds that endanger human health.
1973: EPA mandates a phased-in reduction of lead content in all grades of gasoline.
1974: EPA requires availability of at least one grade of unleaded gasoline, in order to be compatible with 1975 make and model year vehicles. Lead damages the catalytic converters used in these new vehicles to control tailpipe emissions. Catalytic converters are still used in vehicles today.
1996: EPA bans the use of leaded fuel for on-road vehicles (leaded gasoline was down to 0.6 percent of 1996 gasoline sales). Lead is still used in some aviation fuels.
Thanks to coordinated efforts, lead is now absent from gasoline in most of the world. Following the lead phase-out in the United States, the oil refining industry chose to construct additional refining capacity to produce octane from other petroleum products, rather than from renewable sources such as ethanol.
The Clean Air Act Amendments (CAAA) of 1990 were the next major regulation of fuels. Among other things, CAAA requires areas that do not meet ground-level ozone standards to use reformulated gasoline (RFG). RFG has an increased oxygenate content, which helps it burn more completely. As a result, RFG lowers the formation of ozone precursors and other air toxics during combustion.
Petroleum refiners were not required to use any particular oxygenate in RFG, but by the late 1990s, a petroleum product, methyl tertiary butyl ether (MTBE), was used in 87 percent of RFG due to its ease of transport and blending. In the
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