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 measure oxygenates only. 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.