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Emission Standards

USA: Cars and Light-Duty Trucks: Tier 3


Tier 3 emission standards for light-duty vehicles were proposed in March 2013 [2839] and signed into law on March 3, 2014 [2999]. The Tier 3 standards—closely aligned with California LEV III standards—are phased-in over the period from 2017 through 2025. The regulation also tightens sulfur limits for gasoline.

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The structure of Tier 3 standards is similar to the Tier 2 standards—manufacturers must certify vehicles to one of seven available “certification bins” and must meet a fleet-average NMOG+NOx emission standard for their vehicle fleet in a given model year. The standards are more stringent than Tier 2 standards and include a number of other important changes:

  • Both the certification limits (bins) and the fleet average standards are expressed using the sum of NMOG+NOx emissions,
  • The bins are named using their corresponding NMOG+NOx limit in mg/mi. The highest emission bin—Bin 160 (NMOG+NOx = 160 mg/mi)—is equivalent to Tier 2 Bin 5,
  • The fleet average NMOG+NOx emissions must reach 30 mg/mi (Bin 30 = Tier 2 Bin 2) by 2025,
  • The required emission durability has been increased to 150,000 mi, up from 120,000 mi.
  • Gasoline vehicles are tested—for exhaust and evaporative emissions—using gasoline containing 10% of ethanol (E10).

The Tier 3 rule also includes emission standards for heavy-duty vehicles (HDV), such as heavy-duty pick-ups and vans, chassis-certified as complete vehicles.

The definitions of vehicle categories, including light-duty vehicles (LDV), light-duty trucks (LDT) and medium-duty passenger vehicles (MDPV) are consistent with the Tier 2 definitions.

Information and regulatory announcements on Tier 3 regulation can be found in the EPA Tier 3 web page [2838].

Tier 3 FTP Standards

Certification Bins

Manufacturers must certify their vehicles to one of the seven emission bins shown in Table 1. Vehicles are tested over the FTP-75 test procedure (the NMOG+NOx limits must be additionally met over the HFET cycle). The standards are applicable to all vehicles, regardless of the fuel type.

Table 1
Tier 3 certification bin FTP standards (150,000 miles)
Bin 16016034.24
Bin 12512532.14
Bin 707031.74
Bin 505031.74
Bin 303031.04
Bin 202031.04
Bin 00000
* In MYs 2017-20, the PM standard applies only to that segment of a manufacturer’s vehicles covered by the percent of sales phase-in for that model year, Table 3.

Bin 160 NMOG+NOx limit is equivalent to the sum of NMOG and NOx limits in the Tier 2 Bin 5. Bin 30 emissions are equivalent to Tier 2 Bin 2.

The EPA bins and the California LEV III emission categories have the same emission limits, to harmonize the federal certification testing with California requirements.

Fleet Average NMOG+NOx Standards

Tier 3 standards include a fleet average NMOG+NOx limit that must be met by each manufacturer. The fleet average NMOG+NOx limit is phased-in starting from 2017, and reaches 30 mg/mi in 2025 (Table 2). This final Tier 3 fleet average limit is applicable to all vehicle categories—an important change from the Tier 2 regulation that allowed more relaxed fleet average emissions from heavier vehicle categories.

Table 2
Tier 3 fleet average NMOG+NOx FTP standards (mg/mi)
Vehicle Category2017*20182019202020212022202320242025
LDV, LDT1867972655851443730
LDT2, LDT3, LDT4, MDPV1019283746556473830
* For LDVs and LDTs over 6,000 lbs GVWR and MDPVs, the fleet average standards apply beginning in MY 2018.

PM Standards

Tier 3 PM standards apply to each certified vehicle separately, they are not fleet average standards. However, due to uncertainties in regards to future vehicle technologies—such as gasoline direct injected engines or start-stop systems—and PM measurement methods at ultra-low emission levels, EPA adopted a five year phase-in period for PM standards. The phase-in schedule is based on percentage of sales, Table 3. A relaxed in-use FTP PM standard of 6 mg/mi applies during the phase-in period.

Table 3
Phase-in of Tier 3 PM FTP standards (mg/mi)
Percentage of sales20%*20%40%70%100%100%
Certification standard333333
In-use standard666663
* Manufacturers comply in MY 2017 with 20% of their LDV and LDT fleet under 6,000 lbs GVWR, or alternatively with 10% of their total LDV, LDT, and MDPV fleet

Supplemental Exhaust Emission Standards

SFTP Testing. In addition to FTP testing, vehicle emissions are measured over the supplemental FTP (SFTP) cycles, including the US06 and SC03. The composite SFTP emission result is calculated using the same formula that was used in Tier 2 regulation:

SFTP = 0.35 × FTP + 0.28 × US06 + 0.37 × SC03(1)

NMOG+NOx Standards. Manufacturers voluntarily determine the specific SFTP NMOG+NOx standards for the certification of each vehicle family. (These self-selected standards are analogous to family emission limits, FEL, used in heavy-duty highway engine standards.) Such self-elected standards must not exceed 180 mg/mile. The fleet average SFTP decreases from 103 mg/mi in 2017 to the final 50 mg/mi in 2025 (Table 4).

Table 4
Tier 3 fleet average NMOG+NOx SFTP standards
NMOG+NOx (mg/mi)1039790837770635750
CO (g/mi)4.2
* For LDVs and LDTs over 6,000 lbs GVWR and MDPVs, the fleet average standards apply beginning in MY 2018.

US06 PM Standards. The SFTP standards for PM are to be met over the US06 test, representing aggressive highway driving. Similar to the FTP standards, the US06 PM standards are phased-in over a five year period based on the percentage of sales, Table 5. The PM standards are applicable to each vehicle family (i.e., not fleet average). In-use standards are more relaxed than the certification standards.

Table 5
Phase-in of Tier 3 PM US06 standards (mg/mi)
Percentage of sales20%*20%40%70%100%100%100%100%
Certification standard1010666666
In-use standard101010101010106
* Manufacturers comply in MY 2017 with 20% of their LDV and LDT fleet under 6,000 lbs GVWR, or alternatively with 10% of their total LDV, LDT, and MDPV fleet

Vehicles that do not meet the final Tier 3 PM standards (a declining percentage of sales through MY 2021) are referred to as interim Tier 3 vehicles.

Useful Life

Tier 3 standards apply over a useful life of 150,000 miles or 15 years, whichever occurs first. This requirement is identical to the California LEV III program approach.

However, the Clean Air Act precludes EPA from requiring a useful life longer than 120,000 miles for lighter vehicles, including LDVs and LDT1s. Therefore, manufacturers are allowed to certify their LDV and LDT1 vehicles to a useful life of 120,000 miles (and 10 or 11 years, depending on vehicle category and weight).

If any vehicle families are certified to the shorter useful life period, a proportionally lower numerical fleet-average NMOG+NOx FTP standard applies, calculated by multiplying the respective 150,000 mile standard, Table 2, by 0.85 and rounding to the nearest mg/mi. Standards for other pollutants and other test cycles (such as SFTP) remain the same regardless of the chosen useful life period.

Tier 3 Fuel Standards

The Tier 3 fuel standards require that federal gasoline contains no more than 10 ppm of sulfur (down from 30 ppm) on an annual average basis by January 1, 2017. Eligible small volume refiners must comply by January 1, 2020. The regulation maintains the prior per gallon caps—80 ppm at the refinery gate and 95 ppm downstream.

An important purpose of the updated sulfur standard is to reduce the negative effect of sulfur on three-way catalyst performance; facilitating the achievement of the 150,000 mile full useful life emission limits. The 95 ppm downstream sulfur cap will still be a challenge for some sulfur-sensitive catalyst technologies, such as NOx adsorbers, that are used on direct injection, lean burn gasoline engines. Many lean burn catalyst technologies require a sulfur cap on the order of 10 ppm.

Other Provisions

Evaporative Emissions. The Tier 3 regulation introduces new, more stringent evaporative emission standards. These include standards over 2-day and 3-day evaporative emission tests, which vary by vehicle categories and range from 0.300 to 0.500 g/test for light-duty vehicles and MDPVs, with 0.600 g/test for onroad gasoline-powered heavy-duty vehicles. The adopted evaporative emission standards also include a new "bleed test" and a new "leak test" requirements.

Gasoline test fuel containing 10% ethanol (E10) is used for evaporative (as well as exhaust) emission testing.

On-Board Diagnostics (OBD). EPA adopted and incorporated by reference current OBD regulations by the California ARB, effective for MY 2017, that cover all vehicles except those in the heavier fraction of the heavy-duty vehicle class.

Direct Ozone Reduction (DOR). Manufacturers continue to obtain an NMOG credit towards the combined NMOG+NOx standard for use of DOR technologies, such as radiators coated with ozone destruction catalysts. California methodology continues to be used for demonstrating the effectiveness of the technologies. The credit is limited to 5 mg/mi NMOG.

High Altitude Standards. Tier 3 standards introduce high altitude relief provisions to account for the lower air density and slower catalyst light-off at high altitudes. High altitude conditions are defined as those with a test altitude of 1,620 meters (5,315 feet) above sea level. (Under Tier 2, the same FTP emission bin standards applied to vehicles tested at both low and high-altitude.)

Manufacturers are allowed a limited relief for certification testing at high altitude. For sea-level certifications to Bins 20, 30, and 50, a manufacturer can comply with the next less-stringent bin for testing at high altitude. For example, a manufacturer can certify to Bin 50 for testing at high altitude versus Bin 30 at sea level. For vehicles certified at sea level to Bins 70 and 125, manufacturers can comply with standards 35 mg/mi higher (i.e., 105 mg/mi and 160 mg/mi, respectively). There is no high altitude relief for vehicles certified to Bin 160.

Enrichment Limitation for Spark-Ignition Engines. To prevent emissions from excessive enrichment in areas not fully encountered in the test cycles, the Tier 3 regulations impose limitations in the frequency and magnitude of enrichment episodes for spark-ignition light- and heavy-duty vehicles.

DEF Refill Interval—For light-duty vehicles and light-duty trucks equipped with SCR aftertreatment, a minimum DEF (urea solution) refill interval is 4,000 miles [3408].

Phase-In Period Provisions. The Tier 3 standards include a number of provisions—such as alternative compliance options, flexibilities and requirements—applicable during the Tier 3 phase-in period. Some of these provisions include:

  • Relaxed In-Use Standards. Relaxed in-use NMOG+NOx standards—40% less stringent than the certification standards—apply to all vehicles certified to Bins 70 and cleaner as interim or final Tier 3 vehicles. The relaxed in-use standards apply during the entire percent phase-in period (i.e., through MY 2021).
  • Transitional Tier 3 Bins. Two transitional Tier 3 bins—Bin 110 and Bin 85, that have FTP NMOG+NOx standards of 110 mg/mi and 85 mg/mi, respectively (i.e., the sum of the NMOG and NOx values from the Tier 2 bins 3 and 4)—are available through MY 2019.
  • Interim 4,000 Mile SFTP Standards. Interim Tier 3 vehicles (i.e., vehicles which do not meet the final Tier 3 PM standards) must meet 4,000 mile SFTP standards, consistent with the existing Tier 2 and LEV II program requirements. This approach is designed to prevent excessive emission levels from individual vehicle models being masked by the averaging of the manufacturer’s fleet emissions.

ABT Program. Tier 3 regulations include an emission averaging, banking, and trading (ABT) program similar to those that have historically been a part of most EPA emission control programs.