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US EPA to update NOx emission standards for heavy-duty engines

14 November 2018

The US Environmental Protection Agency (EPA) announced the “Cleaner Trucks Initiative” (CTI)—a future rulemaking to update standards for NOx emissions from highway heavy-duty (HD) trucks and engines. The EPA intends to publish a proposed rule in early 2020.

The EPA expects that “any update to the standards will result in significant mobile source NOx reductions”, but the agency has not released any NOx emission limits or ranges it may be targeting in the rulemaking. From 2007 to 2017, US NOx emissions dropped by more than 40%, but “there is more work to be done”, the EPA said. It is estimated that heavy-duty trucks will be responsible for one-third of NOx emissions from the transportation sector in 2025.

In addition to NOx emissions standards, the CTI will simplify certification of compliance requirements for HD trucks and engines. Areas of deregulatory focus will include onboard diagnostic requirements, cost-effective means of reassuring real world compliance by using modern and advanced technologies, the deterioration factor testing process, and concerns regarding annual recertification of engine families.

The current NOx emission standard of 0.2 g/bhp-hr (FTP) is a part of the US EPA 2007 HD emission standards, which were finalized in December 2000 by the Clinton administration and re-confirmed in February 2001 by the Bush administration. As most manufactures opted for a phase-in fleet-average NOx compliance approach from 2007 to 2009, full compliance with the 0.2 g NOx standard started across the industry in 2010—forcing the adoption of urea-SCR aftertreatment on all HD diesel engines.

The need for more stringent NOx emission standards was first voiced by California, where further control of NOx emissions from HD engines is required to meet the state’s long term air quality goals. In 2014, the California Air Resources Board (CARB) adopted Optional Low NOx Standards, with three optional NOx emission limits of 0.10, 0.05 or 0.02 g/bhp-hr. Since then, CARB has repeatedly stated their plan to develop—together with the EPA or alone—mandatory low NOx standards for heavy-duty engines, targeting a NOx limit of 0.02 g/bhp-hr (a 90% NOx emission reduction from the current standard of 0.2 g). Achieving the 0.02 g standard would likely require the addition of a second, close-coupled SCR (ccSCR) system and other upgrades to the current HD engines and their aftertreatment.

In December 2016, in the final weeks of Obama administration, the EPA decided to support the California ultra-low NOx drive and announced that it initiated rulemaking for low-NOx HD emission standards. However, the program appears to have been dormant. The re-activation of the ultra-low NOx program in the form of the Cleaner Trucks Initiative by the Trump administration came as a surprise to many industry observers. The EPA action may be a part of a bigger picture that also involves the ongoing dispute between the EPA and CARB over the light-duty GHG emission and fuel economy standards. However, CARB has not yet issued a statement on the EPA initiative.

Industry reactions to the CTI announcement have been overwhelmingly positive. The list of groups and companies that voiced their support includes the Truck and Engine Manufacturers Association (EMA), Diesel Technology Forum and Cummins. Heavy-duty engine and vehicle manufacturers support a single, national emission program, as opposed to two parallel sets of standards—one federal and one in California and other Section 177 states. Manufacturers would also welcome simplified emission certification and compliance requirements.

Reactions from environmental and public health groups have been more cautious. Groups including the Sierra Club and the American Lung Association said the idea is encouraging, but its effect ultimately depends on the details of the rulemaking which are still unknown.

Source: US EPA