July 24, 1996 MOBILE5a Model Frequently Asked Question #1 Question: How can I model the federal reformulated gasoline (RFG) program using MOBILE5a? Answer: MOBILE5a has the capability to model Phase 1 (starting in 1995) and Phase 2 (starting in 2000) of the RFG program based on the Simple Model used in the original proposed RFG rulemaking.[1] Below are the steps and background information needed to model the RFG program. 1. The fuel volatility class flag, which is the second variable in the local area parameter record, must be set to reflect the fuel volatility class of the area being modeled. The user may enter A or B to instruct MOBILE5a to model Region 1 (generally in the south) and C, D, or E to model Region 2 (generally in the north).[2] Please see page 2-38, section 2.2.10 in the MOBILE5 User's Guide for more information.[3] 2. The RFG flag, which is the tenth and last variable in the local area parameter record, must be set to 2 in order to model an area's RFG program. (See page 2-45, section 2.2.16, and page 2-85 in the MOBILE5 User's Guide). 3. The user has the option of indicating whether summer (July) or winter (January) will be modeled. The default month/season for MOBILE is January/winter in the year of interest. If the user needs to model summer, then the numeral 7 must be entered in the Scenario Descriptive Record in the sixth variable position (See page 2-51, section 2.3.2, and page 2-88 of the MOBILE5 User's Guide). If summer is being modeled (enter 7), then MOBILE5a will calculate emission factors, including the effects of RFG, based on the following rules:  The model assigns a value of 2.1% fuel oxygen content by weight and user-supplied oxygenated fuel parameters will be ignored.  The model applies an adjustment factor to the exhaust emission factors to reflect sulfur reduction in the reformulated fuel.  The model assigns ether oxygenate a 100% market share.[4]  User-supplied RVP and oxygenated fuel inputs are overridden by MOBILE5a defaults listed below: Phase 1 - Region 1 (south) RVP = 7.1 psi - Region 2 (north) RVP = 8.0 psi Phase 2 - Region 1 (south) RVP = 6.8 psi [4] - Region 2 (north) RVP = 7.5 psi [4] If winter is being modeled (the default setting), then MOBILE5a will calculate emission factors, including the effects of RFG, based on the following rules:  The model will use the RVP values that the user specifies in the fifth and sixth variable positions in the local area parameter record (Please refer to page 2-37, section 2.2.8, and page 2-85 in the MOBILE5 User's Guide).  The model applies an adjustment factor to the exhaust emission factors to reflect sulfur reduction in the reformulated fuel.  MOBILE5a will assume a 2.1% oxygen content by weight and a 70/30 percent market split between ether and ethanol blends, respectively, that allows a higher RVP for reformulated fuel splash-blended with ethanol . The user may override this default by using the OXYFLG option in the local area parameter record (see page 2-43, section 2.2.14). When choosing to override the default value, a user must input into the oxygenated fuels descriptive record the oxygen content by weight that is greater than 2.1% and any oxygenate market share split as long as the sum of the split is 100%. The user also will have to determine whether to switch on the RVP waiver by inputing the numeral 2 at the end of the variable string (see page 2-60, section 2.3.9). Setting this flag to 2 will increase the user-supplied RVP level to account for splash-blending of the ethanol market share. For further info email: mobile@epamail.epa.gov ________________________________________ [1] Since MOBILE5a bases its calculations for the RFG program on the Simple Model and the proposed rule, there will be a discrepancy between estimates based on MOBILE5a and those based on the Complex Model used in the final version of the RFG rulemaking. The next update to the model (MOBILE6) will revise RFG effects base on the Complex Model and the final RFG rulemaking. For more information about the Complex Model, please call David Korotney of the OMS Fuels and Energy Division at (313) 668-4507. [2] In the MOBILE5a model, it does not make any difference whether A or B is entered for Region 1 and C, D, or E for Region 2. The ASTM volatility limit classes have been superseded by EPA regulations on summer fuel volatility and RFG ("Volatility Regulations for Gasoline and Alcohol Blends Sold in Calendar Year 1992 and Beyond," 55 FR 23658, June 11, 1990.), which divide the country into northern and southern regions. MOBILE5a maps the old ASTM fuel volatility limit classes to the two regions. [3] The MOBILE5 User's Guide can be downloaded from the OMS bulletin board section of the Technology Transfer Network (TTN) at 919/541-5742 or through TELNET at ttnbbs.rtpnc.epa.gov. The user's guide is also available from the EPA internet server: http://www.epa.gov/omswww/omshome.htm gopher://gopher.epa.gov:70/11/offices/air/oms ftp://ftp.epa.gov/pub/gopher/oms/ [4] As previously noted, RFG estimates in MOBILE5a are based on the Simple Model and the proposed RFG rules (40 CFR, Part 80; FR Vol. 56, No. 131, July 9, 1991). The RFG FRM includes different requirements for Phase 2 RVP limits (6.7 psi in both Regions 1 and 2), and different ether/alcohol-blend market shares. The user can alter the assumed ether/alcohol blend market shares through the oxygenated fuel descriptive record; the user cannot alter the Phase 2 RVP limits, which will be updated in MOBILE6 to reflect the RFG FRM.