Answers to Your Questions about Greenhouse Gas, Tier 3 Vehicle Standards

By Glade Sowards

emission standardsOn April 2, 2018, the Environmental Protection Agency (EPA) announced its intention to revise the model year (MY) 2022-2025 light-duty vehicle GHG standards. Division of Air Quality (DAQ) staff received questions from the public about how this action might affect air quality in Utah and state efforts to meet federal air-quality standards in nonattainment areas.

While the announcement may limit progress in reducing greenhouse gas (GHG) emissions, DAQ cannot make a comprehensive determination on the potential impacts of the EPA’s announcement on the emissions that contribute to Utah’s winter and summer air-quality challenges until revised standards are finalized and DAQ’s emissions models are updated to reflect these revisions.

What are the standards in question?

In 2012, EPA established the second phase of light-duty vehicle greenhouse gas (GHG) standards covering MY 2017-2025. Like the Phase 1 standards (which covered MY 2012-2016 vehicles), the Phase 2 standards were established in parallel with National Highway Traffic Safety Administration (NHTSA) corporate average fuel economy (CAFE) standards, since vehicle GHG emissions largely correspond with fuel consumption. The Phase 2 GHG/CAFE standards are shown in Table 1 below, with the years affected by EPA’s April 2, 2018, action shaded in blue.

Table 1 – Projected 2017-2025 Fleet-Wide CO2 and Fuel Economy Compliance Levels

Emission standards

As part of the Phase 2 rulemaking, EPA conducted a Midterm Evaluation (MTE) of the standards for MY 2022-2025 to ensure that market conditions and technological developments remain conducive to achieving the GHG targets for those years. On January 12, 2017, former EPA Administrator Gina McCarthy completed the required MTE by signing a final determination to maintain the proposed GHG standards for MY 2022-2025.

On March 15, 2017, newly-appointed EPA Administrator Scott Pruitt announced his intent to reconsider former Administrator McCarthy’s final determination and make a new final determination by no later than April 1, 2018. The new final determination, signed on April 2, 2018, found that the MY 2022-2025 standards are “not appropriate” and should be revised.

Any revisions to the standards will require new rulemaking and public comment.

Does this impact Tier 3 vehicle standards?

While the Phase 2 GHG standards cover the same MY 2017-2025 time period as the Tier 3 vehicle standards, they are, in fact, separate standards with different aims. The GHG standards address carbon dioxide (CO2) emissions, with targets expressed in grams/mile. These targets coincide with CAFE fuel economy requirements, which are expressed in miles per gallon (mpg).

By contrast, the Tier 3 vehicle standards are aimed at reducing non-GHG emissions, such as direct particulate matter (PM), nitrogen oxides (NOx), and nonmethane organic gas (NMOG), pollutants that contribute to particulate, ozone, and other air-quality problems. The Tier 3 vehicle standards, like the GHG standards, establish emission limits for these pollutants in grams/mile. The Tier 3 standards, shown in Table 2 below, are between 70 and 80 percent cleaner than the Tier 2 standards that came before them.

Table 2 – Tier 3 Certification Bin Standards (FTP; 150,000 miles)

Emission standards

Fuel consumption typically increases with vehicle size, so GHG emissions tend to be higher for larger vehicles like trucks and SUVs. However, due to the tremendous strides made in vehicle emission-control equipment over the past 50 years, emissions of non-GHG pollutants, such as direct PM, NOx, and NMOG, have become somewhat decoupled from fuel economy, to the extent that even larger SUVs and trucks are capable of meeting the stringent emissions limits established under Tier 3.

What is the time frame for revising the standards?

To revise the MY 2022-2025 GHG standards, the EPA will need to begin a formal rulemaking process. EPA has indicated that it will, in partnership with the National Highway Traffic Safety Administration, “… initiate a notice and comment rulemaking in a forthcoming Federal Register notice to further consider appropriate standards for model year 2022-2025 light-duty vehicles, as appropriate.” This process will likely take over a year or more to complete.


How will changes to the light-duty vehicle GHG standards impact Utah’s air quality?

Because the Tier 3 standards are independent of the GHG standards, vehicles sold under the revised GHG and CAFE targets would still be subject to the pollutant emission limits established under Tier 3. Specifically, manufacturers would still be required to meet both the 30 mg/mile fleet average requirement for combined NMOG and NOx emissions and the 3 mg/mile per vehicle requirement for PM emissions — pollutants that contribute to Utah’s wintertime particulate and summertime ozone challenges.

DAQ cannot estimate the ultimate impact of EPA revising the MY 2022-2025 GHG standards until the revisions are made public and finalized by EPA and the models DAQ scientists use to evaluate vehicle emissions are updated to reflect these revisions. Regardless, DEQ remains committed to protecting and improving Utah’s air quality and will continue its ongoing efforts to address Utah’s air-quality challenges.

Want to know more? Visit the EPA site for more information on the MTE process and EPA’s April 2, 2018, announcement.


Glade Sowards

I am an environmental scientist in the Division of Air Quality  Policy Section. I have a B.A. in Economics and Environmental Studies from Grinnell College and an M.S. in Forestry from Michigan Technological University. I worked at the Utah Energy Office for seven years before coming to work at DAQ. I enjoy playing music, road trips, camping, pack rafting, and hiking with my wife, Elizabeth, and our dog, Whiskey.