Fuels and Fuel Additives
Information on Reformulated Gasoline (RFG) Properties and Emissions Performance by Area and Season - Methodology and Explanation
These tables and graphs are based on EPA's analysis of data generated from surveys conducted by the RFG Survey Association, an association of refiners, importers and blenders, as a requirement of EPA regulations. These surveys collect and analyze samples from retail gasoline stations. Each individual survey is conducted during a one-week period. Currently, over 150 surveys are conducted each year, with a total of more than 10,000 samples collected and analyzed. Prior to 1998, the surveys reported only total oxygen and oxygenate content, benzene content, aromatics content and Reid vapor pressure (RVP). In 1998 and subsequent years, the surveys also reported sulfur, olefins and certain distillation properties.
These latter surveys (except those done in California) provide all properties necessary to estimate complex model emissions performance. The complex model estimates volatile organic compound (VOC), toxics and oxides of nitrogen (NOx) emission reductions, relative to a baseline fuel representative of 1990 gasoline, as a function of fuel properties. RFG emission performance standards specify the required reductions from the baseline. The summary tables include average complex model performance calculations for years 1998 and later. Since 1998 and 1999 RFG performance standards were based on the Phase I complex model, the average Phase I model reductions for these years are shown. However, there are differences between the Phase I and Phase II models, so Phase I and Phase II percent reductions are not directly comparable. In order to facilitate comparison of Phase I and Phase II RFG, EPA has calculated the Phase II complex model emissions performance of each 1998 and 1999 sample and reported average Phase II reductions in the summary tables.
EPA calculated the averages contained in the summary tables by first averaging each individual sample property or performance result to obtain a survey average, and then averaging the survey averages to obtain seasonal averages. The summer surveys were conducted between June 1st and September 15th of a calendar year, when RFG must meet a VOC standard. Winter surveys were conducted before or after this time period, and generally before April 1st or after October 15th. The aggregation of the survey results into seasonal averages differs from the compliance calculation methodology used to determine survey pass/fail status. (For example, VOC and summer NOx compliance is based on each individual survey rather than a seasonal average, and compliance with the benzene content maximum is based on an annual average.) However, EPA believes that these seasonal averages provide a good indicator of RFG composition and quality, and that seasonal averages would be useful to many potential users of these data.
Each table shows averages by year and season beginning in 1995, the first year of the RFG program. Some areas will have no results for certain years. In some cases, the area opted in or opted out of the RFG program between 1995 and the latest year of survey data. In other cases (e.g. for smaller opt-in areas), the area was not surveyed every year. Surveys conducted in federal RFG areas in California measured oxygenates only, and these surveys were not conducted after 2005. Winter surveys do not measure RVP, since it is not needed for compliance calculations.
All RFG refiners and importers must meet a standard which limits benzene content, since gasoline benzene content directly affects the amount of benzene emitted. (Benzene is a toxic air pollutant.) They must also meet complex model emissions performance standards for VOCs, toxics and NOx. However, RFG composition varies, and much RFG substantially over-complies with certain standards. Consequently, there is some area-to-area variation in RFG characteristics. The graphs show area-by-area comparisons of RFG benzene content, and complex model VOC, NOx and toxics emissions performance for selected years. The graphs showing year 2000 data also compare Phase I and Phase II RFG.
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