It is very easy to get caught up in the momentum of discussions swirling around us. I am not immune and, quite frankly, neither is the Transportation Energy Institute. In the past few years, as we have sought to better define what we stand for, we have acknowledged that the global priority for transportation is decarbonization and our research has largely been focused on finding sustainable solutions to achieve that goal. Yet, this is shortsighted – there are other priorities to which we must pay attention as well.
I was recently visiting family in Southern California and was reminded of the immediate issues associated with criteria air pollutant emissions like nitrogen oxides and particulate matter, among others. The sky around Los Angeles was about as brown as I have seen it in years. It was a reminder that, while there exists significant concern about the long-term consequences of carbon emissions, there also remains immediate concerns about the quality of air and the impact of pollution on people’s respiratory health. This observation only strengthened in me a conviction to execute the directions of our Board of Advisors to expand our scope.
In May 2023, the Transportation Energy Institute Board of Advisors recognized that a myopic focus on one issue is insufficient, that the challenges facing the transportation sector are more diverse than one singular objective and that our official focus must be more inclusive about the direction in which transportation must evolve. To gain the greatest impact upon transportation emissions, we must consider the full lifecycle of energy and remove the carbon and other harmful emissions wherever and whenever possible. While the Institute will continue to study means for reducing and eventually eliminating carbon emissions, we will also ensure our research incorporates options for reducing other transportation-related emissions and ensuring that solutions seek to preserve access to affordable and reliable transportation energy for all communities.
That said, when we start to review current data it is clear that significant progress has already been made in reducing criteria emissions at the tailpipe. Given our expanded official focus, I thought it would be appropriate at this time to take a look at and share current trends in such emissions from the transportation sector and begin expanding the evaluation beyond the tailpipe to consider the full lifecycle emissions of the transportation sector.
Criteria Pollutant Emissions Over Time
The following chart presents a high level of summary of contributing sources of key pollutants. This data, sourced from the U.S. Environmental Protection Agency, shows that on-highway transportation is the leading source of emissions for only carbon monoxide. It remains a significant contributor of ammonia (NH3) and nitrogen oxides (NOx), but with regards to other sources it is relatively negligible compared with other emissions sources – industrial activities and stationary fuel consumption are much more impactful than transportation for most pollutants.
When we look at each key pollutant over time, we can see significant progress in emissions reductions. With regards to sulfur dioxide, clearly EPA regulations reducing the sulfur content of fuel have had a major positive impact on the sector with transportation SO2 emissions having dropped to very low levels since 2007. Meanwhile, transportation particulate matter and NOx emissions have also demonstrated consistent reductions over time.
With the above achieved reductions, the United States has largely attained the air quality standards set out in the regulations. Our summer 2023 publication, “Decarbonizing Combustion Vehicles – A Portfolio Approach to GHG Reductions,” includes some analysis of criteria pollutants. According to EPA, we are largely in attainment with air quality objectives.
Particulate Matter and NOx
Among the most critical emissions affecting public health are particulate matter and NOx. As is presented in the following charts taken from that report, nearly all modes of transportation have reduced NOx and PM emissions 85-90% since 2000 and are projected to go down even further by 2030.
While transportation is not the primary source of PM emissions (accounting for only 5% of PM emissions), PM does have a significant effect on human health and deserves special attention. And if we expand our notion of transportation emissions into the pollutant lifecycle realm, we can begin to better assess upstream power generation, farmland/biofuel practices, and oil field inputs. Our combustion vehicle study looked at emissions from different vehicle and fuel combinations. The following comes directly from the report (Pages 63-67):
PM pollution poses significant health threats, especially to children and the elderly. EPA estimates that mobile sources (i.e., vehicles) represent less than 5% of PM emissions;the vast majority of PM emissions (73%) result from fires, dust, and agriculture.
According to GREET well-to-wheel (WTW) emission values, today’s gasoline and diesel vehicles’ tailpipe PM emissions are 98.3-100.3% lower than the average 1980 gasoline car, and 97.3-99.4% lower on a WTW basis. Comparing EVs charged using the average U.S. mix electricity to the range of modern gasoline and diesel PM emissions, there is less than a 3% difference between any light-duty vehicle options.
Figure 26 shows the GREET PM emission comparisons alongside other emission estimates for various vehicles and fuels. The most commonly used fuels are highlighted. The emissions analysis shows that when including power plant emissions, EVs have slightly higher PM emissions than estimates for gasoline and diesel PM vehicle levels used by EPA MOVES3 emission inventory and EPA 2019 model year vehicle certification laboratory (Median 2019 MY Cert bar in the figure) and on-road (Median OnRoad Cert bar in the figure) emission values. The EPA MOVES3 emission inventory estimates the gasoline vehicles’ PM value using laboratory clean air; this value is 55% lower than EVs charged by U.S. mix. Adjusting EPA data for on-road air pollution, the EPA MOVES3 value becomes 79% lower than EVs charged using U.S. mix electricity. As can be seen in Figure 26, the full range of credible vehicle emission estimates shows that ICEV PM emissions are equivalent to or below that of EVs, and all are near zero.
The study also addressed PM emissions from the heavy-duty vehicle sector as follows:
Heavy-duty diesel tailpipe exhaust PM emissions have declined 99.8% versus 1990 models according to laboratory tests reported in EPA MOVES3 and CARB EMFAC emission inventories. Figure 28 shows the diesel tailpipe emissions using GREET WTW and EPA MOVES3 laboratory emission rates with adjustment for onroad air pollution consumption. The graph shows newer diesel vehicles with emissions below zero due to the diesel engine’s air pollution consumption and cleanup by its emission controls. With on-road air pollution consumption and cleanup, diesel PM emissions are 99.93% and 100.03% lower than 1990 diesel levels.
Figure 29 expands the view of emissions from tailpipe only (as displayed in Figure 28) to show the WTW emissions reductions from a 1990 model year diesel for several options. A WTW analysis evaluates the PM emissions from fuel extraction, refining or electrical production, and vehicle use emissions. Vehicle PM emissions reductions are nearly equal between EVs and diesels—all are 99.97% or higher. On a WTW basis, diesel-fueled ICEVs reduce PM emissions 94.9-100% and EVs reduce PM emissions 90-94% from a 1990 diesel PM level on a WTW basis, biofueled and petroleum-fueled diesel ICEVs provide greater PM reductions than their battery EV counterparts charged using the U.S. grid mix, and the diesel ICEVs match FCEVs on PM emissions reductions.
The other major category of concern is NOx emissions. Here is an excerpt from our report on that topic (Pages 68-69):
In 1988, California implemented the Low Emission Vehicle program, seeking to reduce criteria pollutants (and especially NOx) by at least 97% so that California might attain the federal ozone standard. At that time, only EVs could provide the 97-98% lower NOx than ICEVs. Today, with the transition to ultra-low sulfur gasoline and diesel enabling higher efficiency catalytic converters on gasoline vehicles and the introduction of selective catalytic reactors to control diesel NOx emissions, ICEVs have reduced criteria emissions 97-99%. In fact, GREET WTW estimates show that, on average, most of today’s vehicle options provide at least 97% reduced NOx from a 1980 model year vehicle emission level. Using current GREET values and EPA certification data, we compared the NOx emission levels of various vehicles and fuels.
Comparing EPA NOx emission certification values for all 2019 vehicle models,79 GREET results indicate that both gasoline-fueled ICEVs’ and EVs’ NOx emissions will continue to decrease in the future, and all vehicle technology options’ NOx reductions from a 1980 NOx level are within 1% of each other. These results are displayed in Figure 31 below.
Reducing the environmental impact of transportation while preserving access to reliable and affordable energy are objectives we should all be able to support. Achieving them together will be a challenge, but it is one to which we can rise and achieve success if we remain open to various viable solutions. Knowing where we currently stand and where we have been is a very useful benchmark against future efforts to further reduce emissions.
The Transportation Energy Institute will continue to study the options that might yield success on all fronts and will push for policy discussions that keep an eye on the objective and not get distracted by hype and aspiration – we need real solutions and they are out there, we just have to work for them.