What is Clean Diesel?

Share This Page

December 01, 2014   |   Diesel Technology Forum

Policy Insider

Background Briefing on EPA Proposed Ozone Standard

The Diesel Technology Forum has prepared this brief Question and Answer document to provide additional background and understanding on how the EPA proposal on November 25, 2014 to lower the National Ambient Air Quality Standards (NAAQS) for allowable ground-level might impact diesel engines and equipment.

The Diesel Technology Forum has prepared this brief Question and Answer document to provide additional background and understanding on how the EPA proposal to lower the levels of allowable ozone might impact diesel engines and equipment.

What is the connection for diesel engines and the EPA Ozone Standard?
Diesel engines do not emit ozone. Rather ozone is formed in a complex atmospheric chemical reaction involving temperature, sunlight, levels of precursor compounds including hydrocarbons, oxides of nitrogen and other emissions.

Internal combustion engines of all kinds - including gasoline, natural gas and diesel engines - are sources of emissions of these precursors - in the case of diesel engines, oxides of nitrogen is of greatest interest; for gasoline engines, hydrocarbons are the predominant ozone-forming emission. (Diesels are inherently low in emissions of hydrocarbons).

Is there a direct relationship between reducing emissions of nitrogen oxides and reducing formation of ozone?
Not necessarily. Ozone formation is variable and unique in each part of the country based on the local meteorology, temperature and climate conditions as well as the mix of sources of emissions - including stationary, area and mobile sources. Some areas of the country would actually see higher levels of ozone formation if emissions of sources of nitrogen oxides were reduced further. In other areas, reducing nitrogen oxide levels could be expected to contribute to lower ozone levels.

Does the diesel industry support adoption of a more stringent ozone standard?
The Diesel Technology Forum does not have a position about the EPA proposed standard at this time.

What are the implications of the more stringent ozone standards proposed today for diesel engine and equipment makers?
If adopted, EPA's proposal to reduce the levels of ozone in the atmosphere may require consideration and adoption of new control strategies by federal and state governments in order to reduce a wide variety of sources of emissions that contribute to ozone formation. Past ozone standards have resulted in federal measures to further reduce vehicle and engine emissions of ozone-contributing compounds.

New technology diesel engines - in heavy-duty trucks, farm and construction equipment, electrical generators, and large engines used for locomotives and marine vessels (starting in 2015) are near zero in emissions of nitrogen oxides.

Getting to these very low levels of emissions has, up until 2010, generally resulted in a loss of fuel efficiency (an increase in fuel consumption), because of adjustments to engine combustion as well as the use of emissions control technology in the exhaust to reach the emissions standards for the full useful lives of the heavy-duty vehicle (435,000 miles).

Are there potential implications of the proposed new ozone standards for users of diesel engines and equipment?
Yes. One of the strategies that EPA has evaluated and implemented in the past is lowering the level of allowable emissions of ozone precursors such as nitrogen oxides from new diesel engines and equipment manufactured in the future. Any changes to emissions requirements for new engines would result in increases in both purchase and operating costs of these engines which would be passed on to purchasers of the diesel engines.

Consideration of further reductions to new engine standards would have to consider that today's new diesel engines are already at near zero levels for ozone precursors such as nitrogen oxides (0.2 g/Brake-Horsepower Hour (BHP-hr.). Further reductions in engine emissions standards - including the nitrogen oxide emission standard - would likely have a negative effect of reducing fuel economy, while imposing additional higher costs on truck owners.

As for existing engines and equipment, State and local governments are responsible for evaluating the need for further reductions of nitrogen oxides from diesel engines and equipment and ultimately proposing any measures for reducing emissions from in-use and existing diesel engines and equipment. EPA would have to approve all such measures included in the State Implementation Plans submitted by states.

How much have emissions of nitrogen oxides been reduced from diesel engines?
Today's heavy-duty diesel engines used in commercial trucks are more than 95 percent lower in emissions of nitrogen oxides than ones manufactured before 2007. New off-road engines and equipment sold in 2014 also have near zero emissions of nitrogen oxides.

 Clean Diesel Progress

 Has new clean diesel technology contributed to reducing ozone levels and meeting clean air goals?
Yes. Earlier this year the American Lung Association noted the national progress towards meeting clean air standards and that half the nation now has air that meets the EPA Clean air standards. The ALA specifically cited the role of clean diesel technology in helping to achieve this clean air progress.

 "We are happy to report continued reduction of year-round particle pollution across the nation, thanks to cleaner diesel fleets and cleaner power plants," said Harold Wimmer, National President and CEO of the American Lung Association.

In its regulatory impact analysis, EPA cited a number of existing regulations and standards to reduce emissions from diesel engines and their benefits.

Could potential control strategies to reduce ozone-forming compounds impact new or existing engines and equipment?
Potentially both. Existing engines and equipment were designed to meet previous EPA standards that allowed for higher levels of NOx emissions. Many of these engines remain in operation, particularly in off-road engines and equipment.

EPA notes that "Retrofitting diesel non-road equipment can provide NOx and HC benefits" and included retrofit strategies in the RIA: Installation of emissions after treatment devices called selective catalytic reduction (SCRs) and rebuilding engines ("rebuild/upgrade kit).

What are the strategies to reduce nitrogen oxide emissions from diesel engines already in use?
Depending on the age, condition and other factors, some existing trucks and equipment and some stationary engines can be modernized and upgraded with emissions control technology that will reduce emissions by up to 85 percent. These devices include oxidation catalysts and in some cases, particularly for stationary engines, like those in generator and pumping applications, selective catalytic reduction (SCR) control systems are an option.

What has been the cost of reducing emissions of ozone-forming compounds from new diesel engines in the past? Will any future proposed controls cost more or less?
The cost has been variable based on type of engine and equipment. Manufacturers estimate the cost increase to customers for compliance with the 2007 and 2010 heavy-duty diesel engine emissions standards to be on the order of $15,000 for a typical class-8 tractor-trailer size truck.

In the Regulatory Impact Analysis for the ozone rule (RIA), EPA notes that the cost per ton of NOx reduced in control strategies to meet the 1997 ozone standards was less than the $10,000 for all strategies BUT heavy-duty diesel engine standards - which cost $11,240 per every ton of NOx reduced. This means that achieving the near-zero levels of emissions came at a higher price per ton than all other control strategies.

Other strategies included the NOx SIP Call, the Clean Air Interstate Rule, Tier 2 vehicle emissions standards, and non-road diesel rules. (RIA p.488).


All News & Resources

Key Contact

Ezra Finkin
Director, Policy

More Policy Insider

Sign up for diesel direct

weekly analysis & commentary from the diesel technology forum