Don't try this at home!

An emissions thought experiment

Increasingly simplistic calls to #Stopburningstuff and #Stickyourselftothings have recently been accompanied by another call: that anyone who challenges the virtues of battery electric vehicles (BEVs) should shut themselves in their garage alongside their idling internal combustion engine (ICE) vehicle for an hour, to see whether they emerge to tell the tale.  This is a rather unethical, and arguably shocking, call that can only cheapen the decarbonisation debate.  It is one thing coming from fringe on-line influencers, but quite another when it comes from well-known, vocal academics.  

The tastelessness of the proposal aside, as Emissions Analytics is committed to using independent testing to understand real-world emissions questions, we have taken the challenge in the form of a thought experiment.  The conclusions from previous newsletters are that modern ICE vehicles are extremely clean relative to older ones, while BEVs have low but non-zero pollutant and carbon dioxide emissions, leaving the optimal policy more finely balanced than typically thought.  Contradicting this, does the challenge, while flippant, hold an essential truth?

Traditional thinking is that toxic fumes would quickly overwhelm you, while a BEV would sit there passively emitting nothing.  Such an experiment tests in microcosm the effects of vehicles on the wider environment.  To see what the likely effects would be, we can forecast pollutant concentrations in our test laboratory using Emissions Analytics’ real-world test data from tailpipes and non-exhaust sources, together with the latest academic research.  

Without wanting to spoil the result, as with so much in the decarbonisation debate, the answer is nuanced and highly sensitive to the selection of the vehicles.  So, it should be emphasised in the strongest possible terms: don’t actually try this at home!  

A typical single European garage is about three metres wide, six metres long, and three metres high – so, about 54 m3 in volume, which is similar to one of our laboratories.  Let’s assume a constant ambient temperature of around 20 degrees Celsius, which is in line with the temperature used for a vehicle certification test.  Vehicle emissions should be estimated from cold start, with the engine having been soaked at the same temperature overnight.  For the thought experiment, it is assumed that no pollutants escape the laboratory, although some gas egress would be necessary to avoid gradual pressurisation of the space.  To avoid accusations of sophistry, we will assume that the ICE vehicle does not have stop/start or other cut-out system engaged, so it is idling throughout.

The laboratory is assumed to contain air with standard background gas and particle concentrations, as shown in the table below.  Also indicated in the table are guides as to when concentrations of each pollutant start having negative human health or cognitive effects (the ‘threshold of harm’), and the immediate danger levels.  These danger levels have been compiled from multiple sources, many from the world of occupational safety.  For some, there are some wide variations in views, but we have tried to pick a fair midpoint for the purposes of illustration.  The references are listed at the end of the newsletter.

First, let’s first take the controversial one: a diesel.  Diesel is a fuel that burns around a quarter more efficiently than gasoline and was for a generation pushed as a route to decarbonisation, only then to be undermined by excessive real-world NOx emissions.  Many air quality problems we suffer today arise from these excesses.  In this case, we have taken a 2021 Volkswagen Passat 2.0 litre 148 bhp front-wheel drive automatic vehicle certified to the latest, strict Euro 6d-ISC-FCM emissions standard.  The results are modelled by using the second-by-second data from an actual real-world test by Emissions Analytics on its EQUA test route, using a Portable Emissions Measurement System (PEMS) augmented by sampling of VOCs onto thermal desorption tubes for later GCxGC-TOF-MS analysis.

During this hypothetical experiment, the vehicle would suck in and then emit about 30 m3 of gas – mainly nitrogen – which is equivalent to about 55% of the total laboratory air volume.  The colour coding indicates whether the concentration after one hour is below the no-harm level (green), or between the no-harm and immediate danger level (amber).  We have also considered whether the process of combustion would use sufficient oxygen from the air to create an asphyxiation risk.  Clear to see is that there is no red, which would indicate immediate danger. 

The most dangerous pollutant, therefore, is nitrogen dioxide, but the forecast levels are still half of the recommended immediate danger levels, despite the amount of air in the laboratory being relatively small.  Even with this worst-case pollutant, if the volume of the laboratory were just 1,438 m3 (about 27 single garages, or the interior volume of an Airbus A380 aircraft), the amount of air would be sufficient to dilute the NO2 to the point of no harm.  Put this car in the open air, and you can see why this powertrain is no longer a problem from an urban air quality point of view.

The experiment was then extended to a modern gasoline vehicle: a Renault Clio 1.0 litre 88 bhp front-wheel drive manual vehicle certified to the Euro 6d-TEMP-EVAP emissions standard.  The main difference in the outcome is for NO2, which is now at a negligible level, and CO, which is about double the diesel vehicle.  Carbon monoxide is rightly feared as highly poisonous gas to humans, and even modern gasoline vehicles emit a significant amount when the engine is cold, but after about two minutes the catalytic converter brings it down to low levels, even in dynamic driving.  As this engine is smaller than the diesel one, the total amount of gas ingested and then exhaled in one hour is only around 12 m3, or 22% of the total volume of the laboratory.

So, for both ICE vehicles, idling in a single garage for an hour, is likely to be negative for your comfort, health and enjoyment, but not fatal.  But are we covering everything?  If we sit alongside a BEV, are there any effects at all?

As we showed in a previous newsletter, VOCs don’t just come out of the tailpipe, but also ‘off-gas’, or evaporate, from the surface of car tyres, as they are substantially made from components of crude oil.  For the Tesla Model Y tested, we found that total VOCs from the tyres was 0.26 grams over one hour.  If these tyres were the only source of VOCs, they would lead to 1.2 ppm in the laboratory at 20 degrees Celsius.  The distinctive smell experienced when entering a tyre warehouse is caused by these VOCs.

There are two further non-exhaust sources of VOCs.  First, fuel evaporates from the fuel tank of an ICE vehicle, even though most gasoline vehicles have ‘canister’ systems to capture as much as possible.  The US Environmental Protection Agency Tier 2 regulations limited these emissions to 0.05 g/mile (0.03 g/km), and they have been tightened significantly since.  If 60 km were travelled in one hour, this would mean evaporative emissions of 1.8 grams.  

Second, a recent academic paper on unreported VOC emissions from road transport highlighted the issue of VOCs from the evaporation (not usage) of screenwash, which contain a mix of mainly alcohols, and which the authors termed “non-fuel, non-exhaust” emissions.  The paper proposes a distance-specific emissions factor of 58 mg/km.  To convert this to grams per second for the purposes of our experiment, we assume the same average speed of 60 km/hour as above for the test cycle the emissions factor was derived for.  That implies total emissions over one hour of 3.5 grams.

In total, these non-exhaust VOCs add up to between 3.8 and 5.6 grams over the hour.  The lower end of the range is for the BEV, as there would be no fuel evaporative emissions, although this may be offset by larger tyres, which is a trend with battery vehicles due to their weight.  The totals for the exhaust alkanes and aromatics were 0.07 grams for the diesel and 0.11 grams for the gasoline.  Therefore, the non-exhaust sources are around 50 times higher than the exhaust VOCs.  In summary, it is best to not to dwell in a small, sealed space, whether it contains an idling ICE vehicle or a BEV that is switched off.

To this approach there is one important caveat.  Change the car to an older one, and the outcome may not be as favourable.  Older gasoline vehicles can have much higher CO emissions, a gas that can have rapid and terminal effects, while older diesel vehicles are famous for their elevated NOx emissions.  The Volkswagen Passat examined here had NOx emissions of 19 mg/km when tested on Emissions Analytics’ combined EQUA route.  This is 76% below the regulatory limit, which is typical of the current generation of diesels.  Wind back only five years, and the emissions would have been more like 400 mg/km.  Being locked in the garage with that car would lead to a poor health outcome.  This is why, fundamentally, the Ultra Low Emission Zone in London, and similar schemes in other countries, are beneficial to air quality, as it is the older vehicles that are a disproportionate source of pollution.

The conclusion from this analysis, apart from avoiding academics with unethical experiments, is that how we think about vehicle emissions is ripe for a complete overhaul.  Most of the impacts come from the tailpipe of older vehicles, and from non-exhaust sources on new vehicles.  Any properly functioning modern vehicle, operating in the open air, will contribute a negligible amount to air quality problems from the tailpipe.  The carbon dioxide problem remains, however, which is the subject of extensive discussion elsewhere.

It remains true that ICE vehicles produce a range of potentially highly toxic compounds from combustion, but at current concentrations when rapidly diluted in the open air, they cease to be a major problem.  But this insight points to the next major are of concern: inside the vehicle cabin.  Pollutants from older vehicles enter through the ventilation system, and VOCs evaporate from the interior materials, to which the driver and passengers are exposed over extended periods within a sealed cabin.  Without the benefits of dilution and filtration in a poor ventilation system, the health exposures can be significant.  We will look at this in our next newsletter…

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References

Carbon dioxide (CO2): https://www.fsis.usda.gov/sites/default/files/media_file/2020-08/Carbon-Dioxide.pdf
Carbon monoxide (CO): https://www.epa.gov/indoor-air-quality-iaq/carbon-monoxides-impact-indoor-air-quality 
Nitrogen oxides (NO2): https://nj.gov/health/eoh/rtkweb/documents/fs/1376.pdf 
Nitrous oxide (N2O) http://www.ilo.org/dyn/icsc/showcard.display?p_card_id=0067&p_version=2&p_lang=en 
Particle number (PN): Emissions Analytics' testing
Formaldehyde (CH2O): https://www.osha.gov/sites/default/files/publications/formaldehyde-factsheet.pdf 
VOCs: https://getuhoo.com/blog/home/understanding-vocs-and-its-effects-on-health

What matters is not the promise of electric vehicles but the actuality

Friday 18 September 2015 saw Dieselgate break.  This was the culmination of a growing dissonance between real-world nitrogen oxide (NOx) emissions and official values for cars and vans.  The rupture was created by governments picking a technology, for the purposes of decarbonisation, where too much was taken on trust within a fragile governance system.  The industry said, rightly, that technology existed to solve the NOx emissions.  The sad reality was that this technology wasn’t deployed in a way that actually reduced NOx enough in practice, and Europe has been dealing with the air quality consequences ever since.

Equivalent failures must not happen as we try new routes to decarbonisation, especially as a generation has been lost with the diesel experiment.  Many air quality problems have been solved even with internal combustion engine technology, with the simpler challenge remaining of updating the car parc.  But decarbonisation is harder, and that is why the promise of battery electric vehicles (BEVs) – the leading contender in light-duty vehicle CO2 reduction – is rightly being scrutinised in exhaustive detail.

Mr Bean actor and car collector Rowan Atkinson’s recent intervention, saying he felt “duped” by the green claims of BEVs, caused a stir, not least because the article appeared in The Guardian, a well-regarded, environmentally conscious UK newspaper.  Much electronic ink has been spilt since, including a subsequent ‘fact check’ by Simon Evans, a climate journalist, in the same publication.  In the spirit of open enquiry and technology neutrality, and given the importance of the topic, we decided to perform a ‘fact fact check.’  In doing this, Emissions Analytics’ only motive is to get as close to the truth as possible, and to acknowledge where we have uncertainties.

In headline, most of what Simon Evans wrote is true, including:

• BEVs won’t solve all the problems associated with car use.  Our comment: very true, and may in some specific cases make them worse.

• BEVs reduce greenhouse gas emissions by two-thirds on a lifecycle basis relative to combustion engine cars in the UK, and the benefits are growing.  Our comment: performing accurate lifecycle analysis is exceedingly hard, and the answer is sensitive to your choice of model and input assumptions.  The two-thirds claim is in the range of plausible estimates, even though Emissions Analytics’ work put the estimate closer to half currently.  Nevertheless, the point stands.

• Emissions from producing batteries are significant, but are quickly outweighed by the in-use emissions from gasoline and diesel cars.  Our comment: how quickly depends on the true lifecycle emissions of the battery, vehicle and fuel, but it is most likely to be in the two to seven year range in the UK (with a wider range across Europe).  Given that a car typically lasts about 13 years, anywhere in this range could be deemed quick.

• Hydrogen is not a mainstream and proven technology in the same was as BEVs are currently, although it may improve too.  Our comment: we agree – it is predicted to improve, and may emerge as the preferred solution for freight transport where the size of the battery is problematic.

• Battery electric technology is the most energy efficient of the alternatives.  Our comment: true, noting that efficiency is an important but not the only consideration.

• Batteries may well outlast the rest of the vehicle.  Our comment: data on battery longevity is encouraging on the whole.

• Lithium-ion batteries do not contain rare earth elements.  Our comment: batteries often contain scarce materials, and rare earths are used in electric motors.
  

However, there is one sentence in the article that we should focus on in particular.  Not that it is incorrect, but that it is true in a dangerous way:

“Indeed, without a widespread shift to EVs, there is no plausible route to meeting the UK’s legally binding target of net zero greenhouse gas emissions by 2050…”  [To clarify, in context “EVs” meant BEVs, excluding hybrids.]  This sentence is important because it is a fact, but it is a fact by definition.  In other words, legislation defines BEVs as zero emissions.  Bingo!  But are they actually zero emissions?  No, as Simon Evans correctly points out.  The manufacturing and electricity-generation emissions are defined out of the equation.  The manufacturing emissions are mostly parked offshore; in practice most of them occur in China, where battery materials and processed before they can be utilised.

So, we have a rapidly looming echo of Dieselgate.  You cannot define your way to decarbonisation.  Repeating the assertion that BEVs are zero emission doesn’t make it any more true.  BEVs in the UK are lower carbon than any current alternative – that is true.  But they come at a cost and with consequences – economically, geopolitically, environmentally, ethically – that make them no more than a highly promising and valid alternative alongside many others.

Let’s not wake up on Tuesday 18 September 2035 to find that we have applied gargantuan resources, failed to reduce CO2 enough, and created new unpleasant side-effects.  

So, Rowan Atkinson may be right for the wrong reasons, and others wrong for the right reasons.  The truth is that Europe, and the world, perhaps cannot afford another Dieselgate.

Webinar: Route map to Net Zero Construction

Emissions Analytics is pleased to welcome Daniel Marsh and Carl Desouza from Imperial College London as our guests to discuss the “Route map to Net Zero Construction.”

Construction machines are typically diesel powered and, depending upon their age and application, can produce relatively high levels of NOx and particulates in urban environments. The construction industry is determined to reduce its environmental impact and meet NetZero targets, but choosing the right path can be daunting when numerous alternatives exist. There is no one size fits all solution.

Our webinar will discuss results from various projects that were led by Imperial College London, alongside Emissions Analytics’ real-world emissions testing services.

This is not intended to be a definitive guide or to provide prescriptive answers, simply to share independent test results and support sharper industry discussion.

What's the problem with biofuels?

One of the many conundra in transportation emissions is why the use of biofuels, promising environmentally friendly reductions in emissions especially for heavy-duty vehicles, is not taking off faster and attracting only limited policy focus. Compare that to the excited talk around battery electrification of trucks, which generously could be described as a challenging solution.

Across the range of biofuels that Emissions Analytics has tested, some patterns become clear. The first observation is that, on average, they tend to lead to very little change in emissions at the tailpipe.  Second, within that average, there tends to be significant variability between vehicle models on the same fuel. Therefore, if comparing tailpipe performance, it is difficult to generalise about the benefits of a particular biofuel, and the expected benefit in any case may be small.

A corollary of the first point is that the proposed benefit of these fuels relies on emissions reduction – often but not always focusing on carbon dioxide (CO2) – located upstream in the fuel production and distribution. This part of the supply chain is often opaque, and not easily subject to independent verification or regulation, as is possible with tailpipe measurement. Therefore, even if the benefits of a biofuel sound attractive, but cannot be verified, it would be right to take a sceptical position. On top of that, there may be secondary, unintended consequences due to competition for scarce resources as biofuel production is scaled, for example by the earlier effects on food supply and prices where raw materials were crops.

Rightly, therefore, many governments have been cautious in incentivising biofuels too categorically. For example, E10 – gasoline containing up to 10% ethanol – has been long proposed in the United Kingdom (UK) and other European countries, yet its adoption has been slow. Natural (fossil) gas, familiar at the pump as either Liquefied Petroleum Gas (LPG) or Autogas, attracts a significant tax advantage in the UK and other countries, yet there is limited forward visibility because the tax advantage is always at risk of withdrawal. Fleets, consequently, have been cautious in converting to natural gas.

To illustrate the dilemma, we can consider test results from two programmes Emissions Analytics has conducted, one covering E10 gasoline, the other compressed natural gas (CNG) and liquefied natural gas (LNG).

Switching from E5 to the higher ethanol E10 gasoline in Europe is often held out as a quick way to deliver large aggregate CO2 reductions as it can be distributed at scale through the existing refuelling infrastructure, to be used both in light- and heavy-duty applications.

To investigate this, we tested E10 on 17 gasoline vehicles in Europe from a wide range of manufacturers. On average, CO2 emissions fell by 0.5%, but this varied at the model level from an increase of 7.1% to a decrease of 6.3%. All were relatively new Euro 5 or Euro 6 vehicles, tested on our standardised on-road cycle made up of urban, rural and motorway elements. Due to the lower energy content of E10, the fuel economy worsened on average by 1.2%, with a similarly wide variation. Perhaps unexpectedly, emissions of nitrogen oxides (NOx) increased by 16.6% on average, from an initial level of 59 mg/km. Carbon monoxide (CO) fell on average by 4.5%.

Therefore, at the tailpipe, the reduction in CO2 was negligible overall. The value of the reduction in CO did not outweigh the effects of the increased NOx emissions, as non-compliant urban air quality is generally caused by excessive NO2 concentrations. For the introduction of E10 to be valuable, the upstream CO2 reduction would need to be large enough to outweigh that increase in NOx emissions. Sufficient transparency around those upstream emissions and any secondary consequences, is not offered by the supply chain and therefore the overall benefit of E10 should rightly be treated with scepticism.

Turning to natural gas, we were invited to be part of the first extensive UK study to assess real-world performance of heavy freight vehicles fuelled by this alternative. The two-year test ending in 2019 was led by biomethane supplier Air Liquide, with three transport operators (Howard Tenens, Asda and Kuehne + Nagel) and three technical partners: Cenex (data monitoring), Microlise (telematics) and Emissions Analytics (real-world testing). The project was supported by Innovate UK.

The goal was to consider the overall performance of gas as a fuel for heavy freight, compared to diesel. A secondary aim was to only use 100% biomethane, which in this case was derived from food waste and supplied by Air Liquide.

Biomethane is chemically similar to its fossil gas counterpart, although the product of a different refining process that starts with biogas that is then improved to increase the methane content and purge it of impurities. Biogas is the raw product of anaerobic decomposition of waste ranging from human and livestock excreta to food waste. Whether from a renewable feedstock or not, gas can be packaged in compressed but gaseous form, or as liquid; it can also be combusted in both spark ignition and compression ignition engines.

Heavy freight vehicles have been produced by different manufacturers to run off both CNG and LNG derivatives. Why the industry has both variants reflects sector immaturity, but also different strengths and weaknesses. For example, when liquefied at minus 160 degrees Celsius, LNG has a higher calorific value for its volume and thereby requires less space for its storage, an important consideration for road freight; but refuelling with LNG requires more safety procedures.

The broader primary energy market is now over 20% gas, following a big rise in recent years, but is dominated by fossil gas drawn from deposits of natural and shale gas, or syngas and coal gas from industrial processes. Of the overall gas market, biomethane, which is renewable as it is made from waste, constitutes just 0.1%, but is growing rapidly¹.

In our consortium test, three different models of gas-fuelled heavy goods vehicle were pitted against their nearest diesel counterparts: rigid/CNG/spark ignition, articulated/LNG/spark ignition and articulated/LNG/compression ignition. The vehicles were drawn from three different fleets and three different manufacturers. The test covered urban, rural and motorway driving to reflect typical duty cycles. While different payloads were tested, we will focus on the 60% payload results here.

On average the gas vehicles emitted 8% less tailpipe CO2 than their diesel pairs, but this disguises variation from a 15% reduction to a 4% increase. It was only the switch to biomethane that delivered consistent, material reductions in well-wheel (WTW) greenhouse gas (GHG) savings: of around 80%, and not less than 76% compared to the diesels. The missing 20% reflects various inefficiencies, losses and a small amount of measured methane slippage, while the CO2 benefits rest heavily on the upstream, energy grid benefits of the fuel itself.

Turning now to air quality, particle number emissions were on average 5.4 x 10¹⁰ #/km (23%) lower on the gas vehicles compared to the diesel counterparts. However, the results were sensitive to payload and duty cycle, variable between vehicles as shown in the chart below.

In contrast, NOx emissions were on average 0.02 g/km (59%) higher on the gas vehicles compared to the diesels. Yet again, however the results were variable between vehicles and conditions, as shown below.

Therefore, there is no consistent pattern in the tailpipe emissions between vehicles and fuels and, consequently, the advantage of gas-powered vehicles rests heavily on the upstream CO2 benefits. With a supplier such as Air Liquide, those characteristics are more open to scrutiny and verification, but scaling and diversification of the supply of biomethane would need to adhere to the same standards to ensure those benefits were delivered.

Recently, UK retailer the John Lewis Partnership announced that it will replace 600 of its heaviest freight trucks with biomethane-powered gas alternatives, prioritising overall GHG emissions while retaining a wide array of options for the rest of its 4,800-strong fleet where electrification may begin to play a serious role for vehicles with a gross vehicle weight (GVW) below 10 tonnes.

In this instance the retailer plans to install its own fuelling infrastructure to guarantee that the gas used is 100% renewable, whereas more broadly it is more typical that governments incentivise the addition of renewable gas to the existing gas supply, highly efficient in that it takes advantage of existing infrastructure, but also subject then to confusion about what proportion of the gas is actually renewable, the fossil and non-fossil components comingling.

The John Lewis example appears to show that the climate-advantage of 100% biogas is now strong enough for management to overcome other drawbacks associated with an immature sector where fuelling infrastructure remains patchy, and where the true business case rests on the need for long-term tax incentives that are by nature uncertain.

Another broader question with no clear answer yet is the exact scalability of renewable gas feedstocks, the typical candidates being food, municipal and sewage waste. As soon as the feedstock becomes biomass from crops or wood products there is the risk of unintended consequence, if those feedstocks might have been put to better use – the subject is hugely complex but supply-chain transparency is an imperative where the climate-benefitting value of the fuel is its primary attraction.

All in all, these complexities may lead to greater focus on synthetic liquid fuels rather than biofuels, as proposed by some academics and industry representatives, and which may have application beyond road transportation such as in aviation. This approach may prove to be more transparent and scalable, and the greater control of the manufacturing process may deliver reductions in air pollutant emissions. In both cases, the results from these test programmes show the essential need for independent real-world testing at the vehicle model level, to avoid policy being based on generalities, hunches and good marketing.

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Footnotes:

1. See: IEA, Outlook for biogas and biomethane: Prospects for organic growth
   World Energy Outlook special report
   Fuel report — March 2020