Impact of Fuel Sulfur on Vehicle Emissions

1. Impact of Fuel Sulfur on Vehicle Emissions Latin American Refining Workshop Mendoza, Argentina November 1, 2006 Nazeer Bhore Fuels Development and Policy Planning ExxonMobil Refining and Supply Co. Fairfax, VA 22037

2. Background • Fuel sulfur is being reduced to 30 ppm and below in many countries • US: Gasoline 30 ppm avg / 80 ppm max, Diesel 15 ppm max • Europe: 50 ppm max current, 10 ppm max 2009 • Japan: 10 ppm max • Many developing countries have higher sulfur specifications, e.g., • Brazil: 80 ppm gasoline and 500 ppm diesel in 2009 • Nigeria: 1000 ppm gasoline and 3000 ppm diesel • Kenya: 1500 ppm gasoline • India: 150/500 ppm gasoline and 350/500 ppm diesel • Issue: What level of sulfur is necessary to provide cost-effective emission control from mobile sources in developing countries • Sulfur level needed for proper operation (enablement) • Additional benefits from lower sulfur (enhancement) • Cost-effectiveness versus other options • S reduction vs. other transport options to achieve similar air quality benefits • Transport vs. non-transport options to achieve similar health benefits

3. US Gasoline Vehicle Emission and Fuel S Standards Max Sulfur Conventional Gasoline HC Oxy Cat NOx 3-Way Cat Tier 1 Tier 2 NLEV • Three-Way Catalyst (TWC) is the main technology for reducing gasoline vehicle emissions • Several generations of TWC operated on relatively high sulfur • Sulfur was reduced for US Tier 2 and for similar standards in Europe and Japan

4. TWC Effective in Reducing Emissions 1997 California Low Emissions Vehicles (CALEV) - Aged • TWC enabled by: • Lead removal • Sulfur < 1000 ppm • Inspection and Maintenance (I&M) Programs critical to sustaining TWC performance ‘X’ vehicles using 30 instead of 500 ppm S gasoline 1 non-working TWC = Gasoline sulfur reduced from 150 ppm to 30 ppm One Euro-III gasoline replaced by one Euro-III diesel One Euro-III gasoline TWC ineffective See next chart for references

5. Low Sulfur Enhances TWC Operation but is Not Necessary for Low Emissions 1989 US Tier 0 1994 US Tier 1 1996 Euro 2 Test Fleets have exhibited a range of sulfur sensitivity with highest sensitivity in 1997-99 California Low Emission Vehicles (CALEV). NOx emissions exhibited greatest sensitivity. Source: 1. Hochhauser et al., “Impact of Sulfur on Gasoline and Diesel Vehicle Emissions”, SAE 06-FFL-189. 2. Rickeard et al. “The impact of Vehicle Emission Standards and Fuel Properties on Vehicle Emissions in China”, Joint Report by VECC of China SEPA and ExxonMobil, August 2005

6. Low Sulfur Enhances TWC Operation but is Not Necessary for Low Emissions 1989 US Tier 0 1997 CALEV aged cat 1994 US Tier 1 1996 Euro 2 1999 CALEV aged cat Test Fleets have exhibited a range of sulfur sensitivity with highest sensitivity in 1997-99 California Low Emission Vehicles (CALEV). NOx emissions exhibited greatest sensitivity. Source: 1. Hochhauser et al., “Impact of Sulfur on Gasoline and Diesel Vehicle Emissions”, SAE 06-FFL-189. 2. Rickeard et al. “The impact of Vehicle Emission Standards and Fuel Properties on Vehicle Emissions in China”, Joint Report by VECC of China SEPA and ExxonMobil, August 2005

7. Low Sulfur Enhances TWC Operation but is Not Necessary for Low Emissions 1989 US Tier 0 1997 CALEV aged cat 1994 US Tier 1 1996 Euro 2 1999 CALEV aged cat China Euro 3 aged cat 2003 Euro 3/4 00 CALEV aged cat Test Fleets have exhibited a range of sulfur sensitivity with highest sensitivity in 1997-99 California Low Emission Vehicles (CALEV). NOx emissions exhibited greatest sensitivity. Source: 1. Hochhauser et al., “Impact of Sulfur on Gasoline and Diesel Vehicle Emissions”, SAE 06-FFL-189. 2. Rickeard et al. “The impact of Vehicle Emission Standards and Fuel Properties on Vehicle Emissions in China”, Joint Report by VECC of China SEPA and ExxonMobil, August 2005

8. Gasoline Sulfur Requirements • Fuel S has had little impact on TWC performance, except for studies conducted on late 1990s US vehicles • Lower S improves TWC performance slightly • Effects of short-term exposure to high sulfur are generally reversible • Sulfur levels below 150 ppm are not needed for good operation of advanced low emission vehicles • Lean NOx traps offer improved fuel economy but require very low fuel sulfur • Alternative fuel economy technologies are sulfur insensitive and are more cost effective • E.g. Hybrids, Cylinder deactivation, etc.

9. Engine Technologies for Reducing Gasoline Fuel Consumption Other technologies: Diesel powertrains, Weight reduction, Automatic manual transmission, aerodynamic design,

10. US Diesel Vehicle Emission and Fuel S Standards NOx Max Sulfur PM PM Trap • Diesel fuel sulfur reductions: • 1991 to help reduce engine-out PM for ‘94 standard • 2007 to enable introduction of after-treatment (DPF)

11. US HDD Standards and Technology • Large PM reduction achieved initially by engine and injection technologies, and later by after-treatment technologies • Fuel sulfur reduction necessary when • Engine and after-treatment technologies are enabled by lower sulfur, or • Sulfate PM emissions are a large portion of total PM 1994 and 2007 PM standards required S reduction Uncontrolled PM level Carbon-based PM Sulfates PM Fuel S, ppm 5000 5000 500 15 Multi-mode combustion Higher injection pressures Particulate filters Adv turbocharging EGR Engine and After-treatment Technologies Combustion system development, Direct injection Adv combustion Hi P injection Aftercooling Computer eng cntrl

12. Diesel NOx After-treatment Options

13. Diesel Sulfur Requirements • Large PM and NOx reductions are possible with engine and injection technologies • Further reductions can be achieved with after-treatment technologies • Reducing sulfur reduces engine-out PM somewhat by reducing sulfate • In vehicles with after-treatment, low levels of sulfur are required to enable the technologies • 50 ppm for DPF and urea-SCR systems • 15 ppm for NOx traps, if used

14. Cost-Effectiveness Analysis • Limited resources can achieve greater air-quality and health benefits when actions are based on thorough scientific and cost-effectiveness analyses • Fuel sulfur reduction options should be compared for cost-effectiveness versus other air emissions mitigation options • Relative cost effectiveness ~ estimated $ per disability-adjusted life year (DALY) • Includes impact of both indoor and outdoor air pollution • Improved vehicle I&M is a cost-effective option for improving air quality • Cost-effectiveness analysis can be extended to include other non-transport health interventions Source: 1. Lyosky K., “Environment Strategy Papers: Health and Environment”, Kseinya Lvovsky, World Bank, October 2001. Annex D. 2. Gwilliams K. et al., “Reducing Air Pollution from Urban Transport”, World Bank, 2004;

15. Conclusions • Vehicle hardware (engine, after-treatment) has much greater impact on emissions than fuel changes • For some technologies, lower sulfur is required to enable adequate performance: most DPF and NOx traps • For many technologies, lower fuel sulfur enhances after-treatment performance, e.g., oxidation and three-way catalysts, urea-SCR • For gasoline, 150-500 ppm sulfur is needed for advanced three-way catalysts • For diesel, • 50-500 ppm sulfur for catalyzed DPF or NOx control via SCR • 15 ppm sulfur for lean NOx traps (if used) • Alternatives for improving air quality should be selected based on cost-effectiveness and should include assessments across multiple sectors • Outdoor versus indoor air pollution • Transport versus non-transport options