There's no such thing as "zero-emission" or "emissions-free" buses or any other class of vehicles, and BEVs and FCVs shouldn't be characterized as such. Non-exhaust emissions (PM from tire wear, brake wear, and road wear) are produced by all vehicles.

According to a peer-reviewed paper from 2018 (Mendoza-Beltran, "When the Background Matters: Using Scenarios from Integrated Assessment Models in Prospective Life Cycle Assessment," Journal of Industrial Ecology, November 2018, https://onlinelibrary.wiley.com/doi/full/10.1111/jiec.12825, Figure 1 (corrected version)), "Particulate Matter Formation" (i.e., primary AND secondary PM2.5) is higher with BEV than a Euro 5 diesel ICEV, at least until electricity grid is >90% renewable.

No vehicle technology is truly "clean." Diesel technology is as "clean" as any other tech, including electric.

On the other hand, a recent study by UC Davis calculates that the battery pack for a 500-mile EV semi-truck would require ~1400 kWh and weigh ~7 tons. Not only are 7 tons of batteries not remotely "eco friendly," they displace 26% of the revenue load compared to diesel trucks. That's more or less confirmed by https://www.youtube.com/watch?v=oJL9MasBFvM (second-half of video). That means that in some cases, 5 BEV semi-trucks would be required to move the same payload as 4 diesel semi-trucks. Will trucking companies go for that? Even apart from the payload issue, the economics of BEV semi-trucks vis-à-vis diesel semi-trucks are questioned in the UC Davis study. Only under the most optimistic scenarios for BEV trucks will they match diesel trucks in cost-to-own, according to that study. As for longevity, current diesel truck engines routinely last 1,000,000 miles without an engine overhaul. Will BEV truck batteries and traction motors last that long? And of course, the whole point of this GCC article is that NOx emissions from the exhaust can be significantly reduced with this technology, while gaining efficiency concurrently. NMHC, CO, PM/PN emissions are already near-zero . The notion that BEVs produce no pollution is also a dream.

Yes... - 100% of 270 diesel passenger vehicles type-approved at Euro 6d-temp have real-world-driving NOx emissions below RDE regulated levels (0.168 g/km), and many have near-zero NOx emissions, based on ACEA testing. Testing by ADAC reveals the some Euro 6d-Temp diesel cars have near zero NOx emissions in real-world testing, and one (MB C220d) has no measurable NOx emissions ( https://www.adac.de/rund-ums-fahrzeug/abgas-diesel-fahrverbote/abgasnorm/rde-messungen-cf-faktor/?redirectId=quer.rde%20messung ). - PN measurements by Emissions Analytics shows newest diesel engines clean the air of particles (https://www.emissionsanalytics.com/news/2020/1/28/tyres-not-tailpipe). - All 2018+ diesel passenger vehicles real-world tested by Emissions Analytics have CO emissions <0.125 g/km. That's >75% below the diesel Euro 6 standard (0.5 g/km), and almost 90% below the petrol Euro 6 standard (1.0 g/km). None of the 500+ diesels tested have failed to meet the Euro 6 diesel standard, regardless of model year. Meanwhile, several Euro 6 petrol vehicles failed to meet the 1.0 g/km petrol standard. - The Advanced Collaborative Emissions Study (ACES), Phase 2, measured zero NMHC (VOC) emissions from U.S. 2010-compliant diesel truck engines under various test cycles. ACES 2 also revealed that over 300 unregulated emissions were 90%-100% below those measured from 2004 diesel truck engines (NiroPAH, Hopenes & Sterenes, Carbonyls, Metals & Elements, Elemental carbon, Dioxin & Furans were all reduced 100%, i.e., these emissions were not detected). - A recent European Environmental Agency report concludes that passenger vehicles' GHG emissions in 2017 in Europe increased for the first time since monitoring started in 2010, thanks in part to the increased market share of petrol vehicles at the expense of decreased market share of diesel passenger vehicles. Petrol passenger vehicles produce 10% to 40% more GHG emissions than comparable diesel vehicles according to that report. - Based on EPA in-use testing, 2019 Ram 1500 4X2 diesel pickup truck had no measurable THC, NMHC, CO, NOx, or PM exhaust emissions as tested on the HWY cycle by EPA itself. The 2020 Chevrolet Colorado 4X2 diesel pickup had <0.002 g/mi NMHC, <0.05 g/mi CO, <0.020 g/mi NOx (SULEV II = 0.020 g/mi), <0.0001 g/mi PM per EPA in-use testing in FTP and HWY test duty cycles. How clean do diesel vehicles have to be before this demonization of diesel ICEV technology stops?

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)

Some recent empirical studies cast further doubt on how effective reducing NOx emissions will be to lower ambient O3 levels. https://www.greencarcongress.com/2020/05/20200512-grl.html https://www.greencarcongress.com/2020/07/20200729-leeds.html

According to a paper published by CARB staff in 2015 (Propper et al., "Ambient and Emission Trends of Toxic Air Contaminants in California." Environ. Sci. Technol. 2015, 49, 11329-11339, https://pubs.acs.org/doi/10.1021/acs.est.5b02766), ambient diesel particulate matter (DPM) concentration in the Southern California Air Basis (SoCAB) was <0.6 µg/m3 in 2012 (Figure 2). According to EPA, the average PM2.5 concentration in 2012 was 15.6 µg/m3 @SoCAB. That would result in DPM accounting for 3.8% of particulate matter at most. The trajectory is down from there and continues to decrease in relative importance (EPA estimates that DPM will contribute ~0.2 µg/m3 in the Western U.S. by 2025). Even in 1998, i.e., long before DPF was in widespread use in diesel vehicles, the "Northern Front Range Air Quality Study" showed that light-duty gasoline vehicles contributed ~60% of PM2.5 carbon at U.S. urban sites tested, and that was 2.5 to 3 times the contribution of diesel exhaust (Page 10-3 of full report). According to a European (UK) report (https://uk-air.defra.gov.uk/assets/documents/reports/cat09/1907101151_20190709_Non_Exhaust_Emissions_typeset_Final.pdf), non-exhaust emissions are a much larger component of vehicular PM10 and PM2.5 emissions than the exhaust. According to Figure 2 and Figure 3 on page 25, exhaust PM emissions will continue to become a smaller and smaller portion of traffic-generated PM10 and PM2.5. So even in Europe it doesn't appear DPM is major component of ambient PM2.5. I agree that there are likely differences in the toxicity of particles. However, GDI petrol cars emit relatively higher levels of PM emissions, and those emissions are ENRICHED in high-molecular-weight PAHs relative to diesel PM. Some of those PAHs are carcinogenic. See https://enrg.io/gasolne-engines-emit-particulates-diesels/ for example. Where's the outrage about those PM emissions?

"...Here, we investigate the mechanisms by which diesel exhaust, a major component of air pollution, induces neurotoxicity...." Except diesel exhaust PM is a very MINOR component of ambient PM2.5. According to CARB's state emission inventory for 2020, diesel exhaust (on- AND off-road) contributed 21.5 tons/day of PM2.5 in California out of a total of 788.3 tons/day from all sources. 21.5/788.3 = 2.7%. What about the other 97.3% of PM2.5 from non-diesel sources? Is PM2.5 from other sources innocuous? Researchers need to start looking for a new villain for a pollution source other than diesel. Some modern diesels have been shown to actually remove particles from ambient air, even relatively clean air in some scenarios (https://www.auto-motor-und-sport.de/tech-zukunft/dieselabgase-partikelmessungen-im-realbetrieb/).

According to a companion study (https://www.emissionsanalytics.com/news/2020/1/8/burning-issue-tyres-and-air-quality), most of the tire PM mass is >PM2.5, and even >PM10. However, there are still relatively high PN emissions in the nano-particle size range.

According to the linked T&E report - "...Combining the per km impact of regeneration on regulatory PN emissions with regulatory PN results on non-regenerating tests did not result in an exceedance of the 6 x10^11/km PN limit. This is also the case when the same calculation is performed for particles larger than 10 and 4nm...." (Page 28) In fact, both vehicles tested easily met the 6X10^11/km standard (<2X10^11/km), even accounting for the more frequent active regenerations claimed in the report and using the smaller particle sizes. There's nothing in the regulation stating that the 6X10^11/km standard is a "not-to-exceed" one.

Why are "diesel engine fumes" being blamed as the source of BC? Another study conducted between 2011 and 2013, i.e., before widespread use of DPF in Europe, showed that the primary source of BC in London is residential wood smoke (Bohnenstengel et al. “Meteorology, Air Quality, and Health in London.” Bulletin of the American Meteorological Society, May 2015, 779-804). The latest diesel vehicles have DPFs that are so effective that they're actually filtering not only dirty urban air, but even relatively clean air (https://www.auto-motor-und-sport.de/tech-zukunft/werkstatt/dieselabgase-partikelmessungen-im-realbetrieb/). BC emissions from these vehicles would clearly be negative!

It should be noted that sufficient concentration of particles is essential for precipitation to occur. Particles act as cloud condensation nuclei. Recent research has found that precipitation efficiency peaks at particle concentrations well above natural background levels.

In addition to the disbenefits of a regulatory strategy that reduces NOx emissions relatively more than VOC/HC emissions, as seen in this study and ozone weekend effect studies, reducing ambient NOx levels relatively more than ambient VOC levels results in more secondary organic aerosol (SOA) formation, based on another recent study - https://www.greencarcongress.com/2017/06/20170622-robinson.html. It's becoming increasingly clear that the regulatory focus on NOx emissions almost exclusively couldn't be more misguided.

This study is obsolete because modern diesels with SCR generally have LOWER NO2 emissions than unfiltered diesels in spite of much higher NO2:NOx ratios from DPF: https://ww3.arb.ca.gov/research/seminars/kirchstetter/kirchstetter.htm#CARBscience

Focusing exclusively on NOx emissions is an incomplete way of assessing exhaust emissions impact on air quality. Lower NOx emissions at the expense of higher emissions of other criteria pollutants is potentially disbeneficial.

A couple of comments about sources of air pollution. Diesel engines are usually the default villain as the source of air pollution. However: - Modern diesel vehicles (i.e., w/DPF) have far fewer PM emission than petrol, both in terms of mass and number - https://www.fleetnews.co.uk/news/environment/2018/06/22/new-diesels-found-to-be-71-cleaner-than-petrol-models - A source apportionment study in London found that PM emissions from residential wood burning was a significantly larger source of ambient PM than diesel vehicles - Bohnenstengel et al., “Meteorology, Air Quality, and Health in London,” Bulletin of the American Meteorological Society, May 2015. - A study published this month concludes that coal-fired electricity generation units are the largest source of ambient ultrafine particles - https://www.sciencedaily.com/releases/2019/03/190312075916.htm

What is the definition of "green car"? Has one been formally established?

Agree with Peter. If you look closely at the recent report from the European Environmental Agency ("Electric vehicles from life cycle and circular economy perspectives; TERM 2018: Transport and Environment Reporting Mechanism (TERM) report," EEA Report No 13/2018 - https://www.greencarcongress.com/2018/11/201081126-eea.html), the results are at best mixed. The GHG emissions and (maybe) local emissions are generally lower for BEV, but human toxicity and ecotoxicity are MUCH higher, mainly from the production phase for the battery. Diesel ICEV generically is not only much lower than BEV in these parameters, it's lower than gasoline ICEV ( see Figures 3.4, 4.2, 6.2, and 6.3).

For what it's worth, Fulcrum claims that they can produce jet/diesel fuel for "less than $1.00/gallon" - http://fulcrum-bioenergy.com/benefits/low-cost-producer/ The cost of ULSD pre-tax is about $2.20/gallon per EIA.

@E-P, The harvesting of forest biomass in lieu of, or in addition to, prescribed burning was just a thought. It's certainly possible that the cost of collecting the biomass may be too high. I'm not clear about your position on biofuels however. You seem to be adamantly opposed to large-scale biofuel implementation here, yet you seem to support it in a comment you made earlier this year: Only replacing 30% of the petroleum used in the USA is setting the sights far too low. A billion dry tons of biomass can make at least 800 million tons of methanol (probably more), which comes to over 260 billion gallons. Total US gasoline consumption, which is about 45% of all US petroleum consumed, is only about 140 billion GPY. Between PHEVs and methanol you could replace 100% of motor fuel and 70% or more of total petroleum.... https://www.greencarcongress.com/2018/01/20180124-biomass.html Can you clarify your position in this regard?

When you have so much money tied up in the assertion that they are correct, the burden of proof should be on those who benefit, not on the skeptics. The same can be said of any technologies or fuels that are outside the "business-as-usual" scenario of primarily continued fossil fuel use for transportation. We likely don't even have full understanding of future ramifications of fossil fuels as they increasingly come from harder-to-process feedstocks like tar sands, for example. I was directly involved with federal and state forestry services' "prescribed burn" programs (controlled burning), mostly in the "smoke management" realm. When I was involved, over 20 million areas of biomass were intentionally burned each year for wildfire management purposes. That of course results in considerable emissions of GHG, PM, NOx, and many other pollutants, completely uncontrolled. That doesn't include the tens of millions of acres burned each year from unintentional wildfires. I always though harvesting at least some of that biomass for fuel production should at least be considered. It may be far too expensive, or have other obstacles, but I personally think it should be looked at. The fuel loadings of forests need to be further reduced, IMHO.

I completely agree. But by the same token, the assertion that most biofuels have negligible benefits is also based on assumptions which could be way off, isn't it? Argonne National Laboratory has an extensive list of publications for data used in GREET (https://greet.es.anl.gov/list.php). Since GREET is updated yearly, the model incorporates data from the very latest research available.

That may be true, but the GREET model is supposed to take all of those emission sources into account, at least as well as they're currently understood. GREET has dozens of tabs within the model that address ancillary emissions from each feeedstock source. It even includes emissions generated from production of agriculture machinery.

What other data do you have regarding GHG emissions from biofuels E-P? According to the latest version of Argonne National Laboratory's GREET model (https://www.greencarcongress.com/2018/10/20181012-greet.html), FT diesel from biomass has 88% lower WTW GHG emissions than fossil diesel (39 g/mile (FTD) vs. 320 g/mile ULSD)). That isn't really negligible, is it?