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Gasoline Composition in the U.S. from Three Datasets 1976-2017
Citation:
Weaver, J. Gasoline Composition in the U.S. from Three Datasets 1976-2017. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-18/258, 2018.
Impact/Purpose:
The purpose of this report is to better understand gasoline composition in the U.S. This is accomplished through reviewing requirements for gasoline composition by various regulatory programs and through presenting historical data illustrating the variation in benzene, methyl tertiary-butyl ether (MTBE) and ethanol for cities across the U.S. The gasoline requirements are outlined and data were obtained from three surveys: the National Institute of Petroleum and Energy Research (NIPER) and its successors (e.g. Northrop-Grumman), the Alliance of Automobile Manufacturers (Alliance), and the U.S. EPA Office of Transportation and Air Quality (OTAQ) in collaboration with industry (i.e., API, NPRA).
Description:
Gasoline composition in the U.S. varies due to market, technical and regulatory factors. Technical factors include seasonal and elevation adjustments for drivability, and needed anti-knock properties. Regulatory factors derive from the Clean Air Act and its amendments. The Clean Air Act Amendments (CAAA) of 1990 created two major types of gasoline in the U.S.: reformulated and conventional gasoline. Since the implementation of this Act, conventional gasoline has tended to be approximately two-thirds of U.S. gasoline and is used in rural areas and smaller cities. Major urban areas are required to use reformulated gasoline (RFG) to meet ozone and carbon monoxide standards and reduce toxic air pollutants. In addition, the CAAA specified that oxygenated gasoline could be used in certain cities to meet carbon monoxide standards in winter. Given the combination of technical and regulatory requirements, and that they have varied over time, the best way to understand the composition of gasoline at any specific location is to evaluate historical data. In this report, three historical datasets were used to trace the historical composition of benzene, oxygenates and alcohols in 15 cities or RFG compliance areas. For the RFG cities, the benzene content dropped when the CAAA mandates went into effect. The median benzene content was consistently less than 1% after 1995. Typically, methyl tert-butyl ether (MTBE) was used to meet the requirement for an oxygenated additive until, either a state ban of ether use was imposed or until MTBE was removed from the fuel supply in 2006. Ethanol use typically replaced MTBE to meet continuing requirements of RFG. In conventional gasoline, benzene was not uniformly limited, but producer baselines were developed. Benzene levels typically decreased over time. When the Mobile Sources Air Toxics Act requirements were imposed in 2011, all U.S. gasoline was seen to have reduced benzene levels. The ether and alcohol content of conventional gasoline varies widely, and is best assessed through historical data. This follows because both ethers and alcohols can be used as octane boosters and they could be used for a variety of market reasons. Oxygenated gasoline, which can be conventional or reformulated, shows the benzene characteristics of its type. The ether and alcohol levels vary seasonally prior to the imposition of national requirements for biofuel usage in 2006 and later years.