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CARB approves Heavy-Duty Low NOx Omnibus Regulation; to cut NOx 90%

The California Air Resources Board has approved a multi-pronged regulation that will significantly reduce NOx emissions from heavy-duty diesel trucks.

The “Heavy-Duty Low NOx Omnibus Regulation” will require manufacturers to comply with tougher emissions standards, overhaul engine testing procedures, and further extend engine warranties to ensure that emissions of NOx (oxides of nitrogen, a key component of smog) are reduced to help California meet federal air quality standards and public health goals.

All components of the new rule will be phased in, allowing engine manufacturers time to prepare for compliance. The NOx standards that engines must meet will be cut to approximately 75% below current standards beginning in 2024, and 90% below current standards in 2027.


Even as California ramps up the numbers of zero-emission electric and fuel-cell trucks on our roads over the next decade and beyond, tens of thousands of new internal combustion trucks will still be sold in our state. This regulation ensures that conventional diesel trucks will run as cleanly as possible at every point in their duty cycle. It takes a significant bite out of smog-forming pollution in every region in the state, and will make a major contribution to cleaning the air in communities close to ports, railyards and distribution centers that are now most heavily impacted by pollution from heavy truck traffic.

—CARB Chair Mary D. Nichols

The regulation is expected to have a significant impact on communities adjacent to railyards, ports and warehouses that typically experience heavy truck traffic. These trucks often idle, move slowly and make frequent stops—all actions that increase NOx emissions. Today’s heavy-duty trucks do not control NOx effectively during such low-load conditions. The new standards will reduce NOx emissions by 90% or more when trucks are operating under these low load real-world operations.

Once it is fully phased in by 2031, the rule is expected to reduce NOx emissions in California by more than 23 tons per day. These NOx reductions are the equivalent of taking 16 million light-duty cars off the road in 2031. (For context, California currently has 26 million registered light duty vehicles).



NOx make O3 which creates heart and lung problems.


Some recent empirical studies cast further doubt on how effective reducing NOx emissions will be to lower ambient O3 levels.



"Low level (ozone) is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC)"

This is the EPA statement on their web site.


EPA also says:

"...EPA's air quality modeling predicts NOx (reduction) disbenefits in the areas identified by some studies as "VOC-limited" (e.g., Los Angeles)...." (Page 2-113)

Source: EPA, "Final Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel Engines."

"...When NOx levels are relatively high and VOC levels are relatively low, NOx forms inorganic nitrates (i.e., particles) but relatively little ozone. Such conditions are called "VOC-limited." Under these conditions, VOC reductions are effective in reducing ozone, but NOx reductions can actually increase local ozone under certain circumstances...." (Page 2-41)

Source: EPA Final Regulatory Impact Analysis: Control of Emissions of Air Pollution from Highway Heavy-Duty Engines.", "U.S. EPA Integrated Science Assessment for Oxides of Nitrogen - Health Criteria (First External Review Draft)." U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-07/093, "EPA Final Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel Engines.", Federal Register / Vol. 72, No. 63 / Tuesday, April 3, 2007, Federal Register / 12/17/2014 (Section E, "Ozone Air Quality")

(Note EPA acknowledges that there are no "VOC disbenefits" in "NOx-limited" areas, but there are "NOx disbenefits" in "VOC-limited" areas)


I am glad to see that Carl brought up the NOx/VOC problem. I would also say that EPA's statement that "NOx reductions can actually increase local ozone under certain circumstances..." is somewhat prudent. This is rather rule than exception, i.e. ozone formation is limited by VOC in close to 100% of all cases (in densely populated areas). This is, for example, manifested in the "weekend ozone" paradox that we see in most cities (also in Europe). Ozone is higher during weekends when heavy-duty traffic is limited. This means that further reduction of NOx from heavy-duty vehicles might actually increase ozone levels. Besides that, reduction of NOx will provide positive health effects, so in general, tighter emission limits on NOx is positive, particularly if also VOC (mainly from light-duty) traffic could be reduced simultaneously. There is, however, most likely a threshold effect when there is no positive impact of further reductions of NOx. Note that the lung itself produces NO (you exhale it). Moreover, NO is a natural compound in the body that has several positive health effects, for example, vascular dilatation, which reduces blood pressure. NO is also first defense against pathogens. Sun exposure and ingestion of nitrates, e.g. from vegetables (for example beet root juice, frequently used in sports), are sources of NO in the body. In contrast, there seems to be no threshold level for particulates. Here, a lower level is always better.


NOx is bad, no attempted spin will change that.

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