17 February 2010

The California Air Resources Board (ARB) has published the long expected proposal for the next tier of emission requirements for light-duty vehicles, known as LEV III. The proposed LEV III program, outlined in an ARB preliminary discussion paper, will be discussed at an ARB workshop to be held on March 2, 2010 in El Monte, California.

“Despite great progress in achieving cleaner air in California, major reductions of criteria pollutant emissions are still required to achieve mandated State and federal ambient air quality standards”, said the ARB. The proposed LEV III standards—applicable through model years 2014-2022—target a fleet average SULEV emission level. The regulation would introduce increasingly tighter fleet average emission limits, eventually reaching 0.030 g/mi NMOG+NOx, equivalent to the SULEV certification bin.

The proposal also considers a voluntary particle number emission standard—the first in North America—that manufacturers could choose instead of the PM mass emission limit.

The LEV III proposal includes a number of important provisions, as follows:

  • Combined NMOG+NOx standard: A combined standard for non-methane organic gases (NMOG) and NOx will replace the current separate standards for NMOG and for NOx. In 2022, the fleet-wide LEV III NMOG+NOx emission standard would be 0.030 g/mi, an equivalent of the sum of the current SULEV standards (NOx = 0.020 g/mi; NMOG = 0.010 g/mi). This fleet average SULEV target represents a 73% reduction relative to the fleet average requirement in model year 2008 vehicles of approximately 112 g/mi NMOG+NOx.
  • Additional certification bins: Three additional certification bins are proposed, including SULEV20, ULEV50 and ULEV70 in addition to the current certification categories of SULEV, ULEV and LEV. The proposed NMOG+NOx emission standards are:
    • LEV = 0.160 g/mi
    • ULEV = 0.125 g/mi
    • ULEV70 = 0.070 g/mi
    • ULEV50 = 0.050 g/mi
    • SULEV = 0.030 g/mi
    • SULEV20 = 0.020 g/mi
  • Medium-duty vehicle standards: New ULEV and SULEV NMOG+NOx standards, as well as fleet average NMOG+NOx standards, are proposed for chassis-certified medium-duty vehicles. (There are no changes to the standards for engine-certified medium-duty vehicles.)
  • PM mass standard: The PM emission standard will be tightened to a level between 2 and 4 mg/mi, from the current 10 mg/mi, to ensure there is no increase in PM emissions from future engine technologies and that particulate filters are used on all diesel engines. Based on input from manufacturers, the ARB believes that a PM standard of 3 mg/mi could be still met in gasoline direct-injection engines without the need for a particulate filter.
  • Particle number standard: The LEV III proposal does not include a mandatory particle number standard due to “issues related to emission testing variability and uncertainty in the health assessment science”. However, an optional PM number standard of about 1012 particles/mi is being considered, which could be chosen by manufacturers instead of the PM mass standard. This number limit would be numerically similar to the Euro 5/6 limit of 6 × 1011 km-1, but the LEV III proposal does not specify the measurement procedure.
  • Durability: The LEV III standards would phase-in a new 150,000 miles durability requirement, compared to the current 50,000 and 120,000 miles standards.
  • Evaporative emissions: All light-duty vehicles would have to meet a more stringent zero evaporative standard, while using more challenging test fuels, such as E10.

A number of technologies are envisioned to reach the new NMOG+NOx emission limits. Cold start emission control may require secondary air injection into the exhaust during rich mixture start-up, cylinder head preheating, lean stratified start-up, ignition retard, and lower thermal mass components for fast engine and catalyst warm-up. Advanced EGR technologies are likely to be used for NOx control. Possible new directions in catalyst technology include integration of catalysts into exhaust manifold for fast warm-up, increased catalyst loadings and cell densities, electrically heated three-way catalysts (TWC), HC traps upstream of TWC, NOx adsorber catalysts for lean gasoline and for diesel engines, and urea-SCR for diesel engines. The ARB paper also notes direct ozone reduction technologies—such as the PremAir radiator coating—which, however, cannot be quantified through regulatory emission testing and would require a system of emission reduction credits.

Source: California ARB