Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 1

TCEQ TxLED Stakeholder Meeting

October 14, 2005

Air Quality Planning and Implementation Division October 14, 2005

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 2

Residual NOx Effects From Low Sulfur Gasoline

• Mobile 6 estimates residual sulfur effects almost exclusively on Tier II vehicles.

– Tier II starts with MY (model year) 2004 cars, with a subsequent year phase-in for light duty pickups.

– This was done in Mobile 6 for two reasons: These vehicles are most sensitive to sulfur effects. Most of the standardized test procedures

evaluating sulfur effects were done on these types of vehicles.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 3

Residual NOx Effects From Low Sulfur Gasoline

• Mobile 6 attempts to make estimations of emission increases due to high sulfur exposure.

• Mobile 6 was not developed to accurately estimate the effect of exposure to low sulfur fuels.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 4

Residual NOx Effects From Low Sulfur Gasoline

• Irreversibility effects are most pronounced with catalysts exposure to high sulfur levels.

• In some cases, exposure to high sulfur levels can irreversibly damage a catalyst.

• In other cases under certain conditions (high catalyst temperatures and rich mixtures) the catalyst can return to almost pre-exposure levels.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 5

Residual NOx Effects From Low Sulfur Gasoline

• Any exposure to high sulfur levels can irreversibly damage Tier II catalysts.

• Therefore, residual credit could be calculated provided that the automobile only experienced low sulfur fuels and was never exposed to high sulfur fuels.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 6

Residual NOx Effects From Low Sulfur Gasoline

• Because Mobile 6 was designed to determine negative impacts of high sulfur gasoline on emission performance, its ability to measure positive effects of low sulfur fuel in a future fleet is limited.

• An effect can be seen using Mobile 6 although the magnitude of the effect is small and mainly driven by the sulfur cap, not the sulfur average.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 7

Why Residual NOx Effects Are Not Being Considered

• Determining refinery averages is fairly straight forward given EPA’s reporting requirements in 40 CFR 80.105 and 80.370.

• Determining refinery caps may be somewhat more difficult.

• Realistically demonstrating that a vehicle has not been exposed to higher sulfur fuel over a three or 4 year period is even more challenging.

Air Quality Planning and Implementation Division • TxLED Stakeholder WHJ: October 14, 2005 • Page 8

Questions?