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Concerns about NO 2 Emissions from Diesel Particulate Filters

Concerns about NO 2 Emissions from Diesel Particulate Filters. John M. E. Storey Fuels, Engines, and Emissions Research Center Oak Ridge National Laboratory (ORNL) Southeast Diesel Collaborative Workshop June 26, 2007 Atlanta, GA. U. S. Department of Energy.

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Concerns about NO 2 Emissions from Diesel Particulate Filters

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  1. Concerns about NO2 Emissions from Diesel Particulate Filters John M. E. Storey Fuels, Engines, and Emissions Research Center Oak Ridge National Laboratory (ORNL) Southeast Diesel Collaborative Workshop June 26, 2007 Atlanta, GA U. S. Department of Energy

  2. How does a Diesel Particulate Filter Work? Trapped PM Cell Plugs Exhaust (CO2, H2O)Out Exhaust(PM, CO, HC)Enter Ceramic HoneycombWall graphic courtesy of MECA

  3. Soot typically burns at > 500 °C A catalytic coating is used to convert NO to NO2 NO2 oxidizes soot Pt or Pd typically used Some filters have a diesel oxidation catalyst before the filter performs same function as coating In many applications, exhaust T still too low for passive regeneration schoolbuses, delivery trucks soot can build up too much Active regeneration a key part of most 2007 diesel vehicles In-cylinder or in-pipe methods to heat exhaust Catalyzed DPFs oxidize the soot at lower temperatures than uncatalyzed DPFs

  4. Why are we concerned about NO2 emissions ? • NOx (NO + NO2) regulated from sources due to ozone non-attainment • important ozone precursor • mobile sources emit primarily NO, atmospheric conversion to NO2 • National Ambient Air Quality Standards (NAAQS) exist for NO2 • 53 ppb annual average; no areas of country in violation as of 2000 • at Watt Rd. “hot spot” we measured 45-60 ppb monthly averages • NO2 exposure may be problematic at elevated levels • at high levels > few ppm, very painful! • at levels > 500 ppb (10X standard), airway constriction • long term exposure to 50-100 ppb associated with morbidity

  5. I-40/I-75 Watt Road Air Quality Studies at Watt Rd.:Location of Roadside, Truckstop, and Ridgetop(Background) Sampling Points Truckstop Elevation: 920 ft Roadside Elevation: 877 ft Ridgetop (Background) Elevation: 1182 ft N W E S

  6. Predicted NOx Concentrations at Watt Rd. truckstop areas – NO2 about 30 - 40% on average up to 260 ppb! ~ 90 ppb NO2 Isopleth Map of Annual Average NOx Concentrations at Watt Road Area (ppb). (Each contour interval equals 20 ppb)

  7. NO2 NO2 NO2 NO2 NO2 NO2 NO2 California says we should care • Retrofit diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) increase NO2 in the exhaust • Potential for high exposure near depots and bus stops • California set rule that NO2/NOx ratio cannot be more than 20%; “natural” ratio about 5-10%. • Biggest problem is with older vehicles with higher NOx engines • Catalyst manufacturer’s response: • lower precious metal content • amount of PM • size to specific application

  8. ORNL experiments with Diesel Particulate Filter active regeneration schemes • Objective: Examine DPF regeneration schemes • fuel usage • PM, other emissions • Approach: Utilize different methods for heating exhaust (150 and 300 °C) • In-cylinder post injection of fuel • Extended main injection of fuel • In-pipe injection (only at 300 °C) • Results: Most rapid heating with post injection schemes • significant differences in fuel penalty • retrofits most likely will use in-pipe • Light-duty diesel engine at ORNL’s Fuels, Engines, and Emissions Research Center • Controls for modifying injection • Flexible exhaust and sampling

  9. The higher temperature of regeneration reduces NO2 Tailpipe NO2/NO, no regen Engine NO2/NOx ratio

  10. Additional Thoughts about NO2 Increases • Potential issue with increasing O3, especially in the East. • What is the mechanism? • O3 is titrated by NO – that is, NO reacts with O3 to form NO2. • Motor vehicle NOx emissions >90% NO • So morning rush removes some O3. • Changing the NO/NOx ratio may short circuit that effect, allowing O3 to build up longer during the day • Much of Atlanta’s O3 is regional transport. • Time in transit may wash out NO2 effect • The decision to retrofit is a balance • Will minor increase in NO2 cause noticeable effect on O3? • Are the health benefits from reduced PM worth possible O3 increase? • Can accommodations be made in the SIP to encourage retrofit? Info courtesy of Doug Lawson – See: Blanchard and Tanenbaum,“Weekday/Weekend Differences in Ambient Air Pollutant Concentrations in Atlanta and the Southeastern United States,” JAWMA,56:271-284. 2006.

  11. Summary • NO2 potential health concern under extreme circumstances • Catalyst manufacturers addressing concerns • Active regeneration schemes no worse than baseline conversion of NO to NO2

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