Tceq txled stakeholder meeting october 14 2005
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TCEQ TxLED Stakeholder Meeting October 14, 2005. Air Quality Planning and Implementation Division October 14, 2005. Residual NOx Effects From Low Sulfur Gasoline. Mobile 6 estimates residual sulfur effects almost exclusively on Tier II vehicles.

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TCEQ TxLED Stakeholder Meeting October 14, 2005

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TCEQ TxLED Stakeholder MeetingOctober 14, 2005

Air Quality Planning and Implementation Division October 14, 2005


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.


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.


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.


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.


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.


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.


Questions?


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