Could vehicle interior air quality become the differentiator of the future?
Cars used to be about speed, power, performance and freedom. Different models often used to offer dramatically different performance and looks. But, not so any more. We are currently in an era of the generic sports utility vehicle (SUV) and identikit low emission vehicles. Electric vehicles “all look alike”, as suggested by the head of BMW recently¹.
But can this last? Will consumers want to buy such seemingly bland offerings, and can manufacturers profit from the undifferentiated? Perhaps we are already beginning to see early signs of a shift. Electrification may turn out to be less about emissions reduction, but rather emblematic of the change in the fundamental proposition of the car away from performance and towards experience. Performance is increasingly constrained through traffic and emissions policy, so consumers may want to make the increasingly dull experience of driving at least more comfortable.
Historically, operating a car delivered ample private benefit and enjoyment, at the expense of an alarming array of environment and health impacts: climate effects through carbon dioxide (CO²) emissions; air quality from tailpipe nitrogen oxides (NOx), particulates and carbon monoxide (CO); air and marine pollution from tyre and brake wear; ozone formation from evaporation of volatile organic compounds (VOCs) from fuel in the tank and construction materials; and noise and many others.
Battery electric vehicles (BEVs) are perceived to be the antidote to this: quiet and pollution free. This is of course not quite true: BEVs create CO² emissions in their manufacture, some noise and perhaps higher tyre wear emissions. Nevertheless, we could get to the point where the environment affects the BEV driver more than the BEV affects the environment.
How could this be true? Road transport collectively is only a minority contributor to air quality problems in 2019 – perhaps only 12% of particles² and 33% for NOx³. The majority of pollution comes from domestic heating, industrial sources and agriculture. This polluted air can enter the vehicle cabin through its ventilation system, exposing the driver to the resulting health risks and discomfort. Therefore, it may well become increasingly the case that the car driver is more a victim of pollution than the cause.
Even without BEVs, there are already some aspects of the internal combustion engine (ICE) which foreshadow this trend. First, due to the efficacy of exhaust after-treatment systems, the levels of CO and NOx are so low in real-world operation that the impact on the environment is negligible. For example, under the latest European Real Driving Emissions (RDE) regulation, the average real-world emissions are 157mg/km from gasoline vehicles and 36mg/km from diesels for CO; and 9mg/km from gasolines and 45mg/km from diesels for NOx. Second, as demonstrated previously by Emissions Analytics, diesel particulate filters (DPFs) are so efficient that there are often fewer particles coming out of the tailpipe than there are in the air of a polluted city such as London⁴.
With this background, consider the scenario where the powertrain element ceases to be a major differentiator between mainstream BEVs. Power may be limited to maximise range, torque could be capped to reduce tyre wear emissions, and tyres may become skinnier to reduce rolling resistance but at the cost of handling. As and when connected and autonomous vehicles hit the road, this pattern may become even more pronounced. Furthermore, the cost of electricity – as low as three cents per kilometre – could mean the operating costs become almost irrelevant. Mainstream cars cease to have a performance dimension. Add to this the relatively few standardised manufacturing platforms and you have vehicles of increasingly similar performance. In this world, how will manufacturers differentiate their products and make decent profits?
Design undoubtedly will remain a key element, both for aesthetics, build quality and cost. Beyond that, with the background of historical air pollution problems and now Covid-19, it may well become the vehicle interior air quality that becomes a major differentiator. What once were major sources of pollution, could now become protective automotive bubbles.
Tesla’s launch of its ‘Bioweapon Defense Mode’ in 2016 was perhaps early evidence of this trend. The data presented by the company for its efficacy involved exposing a vehicle to high levels of particle pollution in an emissions chamber and showed that concentrations of particles by mass⁵ in the vehicle cabin fell from 1,000ug/m3 to undetectably low levels within two minutes, from which they concluded it could protect the vehicle occupant from biological attack⁶.
Grand claims need verifying, especially as to whether laboratory test results carry over into real-world conditions, so Emissions Analytics tested this model on a 2019 Tesla X in the UK. The test followed the protocol set out in an SAE paper published in 2019⁷.
The Tesla X is now equipped with a High-Efficiency Particulate Air (HEPA) filter as standard. In simple terms, the ventilation system has the typical ‘fresh air’ and ‘recirculation’ modes, but also the bioweapon mode too. This HEPA filter is enormous, as shown in the picture below – the installation requiring most of the width of the ‘frunk’. It is approximately 100cm long, 30cm tall and 3cm deep – a volume of over 9,000cm³. This compares to filter volumes on typical mass market cars of 1,000-2,000cm³.
The filter may be large, but it certainly works. In our test, interior concentrations were 94% lower than externally on fresh air mode, and 92% lower on the bioweapon mode during an on-road test – statistically indistinguishable from one another. This is the best performing vehicle we have tested so far. The principal difference between Tesla’s test and ours was that we measured ultrafine particles down to 15nm rather than particle mass. Together, the data suggests excellent protection from both bigger and smaller particles.
To put these results in context, Emissions Analytics tested 97 recent model year light-duty vehicles in the US in partnership with Edmunds⁸. Of all these, the best performing was a 2019 Honda Civic, which reduced particle concentration by 73%. Emphasising the significant differences, the worst performing vehicle was a 2019 Lexus ES, for which particles inside the vehicle were 254% higher than outside. Of the 97 vehicles, 44 had higher concentrations inside than out. This is an unregulated area at the moment, so there is no compliance issue, but there certainly is a potential health issue from chronic particle exposure.
A common driver strategy for protection from exterior pollution – often initiated when the driver senses a malodour – is to engage the recirculation mode on the ventilation system, which wholly or largely circulates, with varying degrees of filtration, existing interior air. This is effective in protecting from pollution ingress from outside, but has the side-effect of allowing CO² to build up in the cabin from the respiration of occupants. Although research is scarce in driving situations, the effects of elevated CO² on cognition have been shown, which leads to the reasonable belief that above 1,000ppm – compared to a background of just over 400ppm – there may be effects on driver safety as well as comfort⁹.
Returning to the Tesla, on fresh air mode, CO² increased by just 8%, while on recirculation the increase was 97%. Impressively, the bioweapon mode saw just a 17% increase. The average increase across the 97-vehicle test on recirculation mode was 15% on fresh air and 79% on recirculation.
From this, it is clear that there is a trade-off between protecting the vehicle occupant from particle ingress into the vehicle on fresh air mode and CO² build-up if recirculation is engaged. While this holds true at the level of the individual vehicle, it is not true at the market level. In other words, there are some models that are good at both, and some bad at both. The chart below plots each of the 97 models tested, plus the Tesla X, for particle infiltration on fresh air mode against CO² build-up on recirculation.
For particle number, the values are the ratio between concentrations in the interior and exterior air, so a value of one means they are the same on average. For CO², a value of zero means there is no increase in interior concentrations compared to the baseline. On this latter measure the Subaru Impreza showed the worst performance, in contrast with the best from the Chevrolet Suburban – as indicated on the chart.
In short, there is a wide diversity of results and no obvious pattern, whether it be by manufacturer, vehicle size or powertrain. The most conspicuous activity currently is from premium manufacturers, whose buyers perhaps have the greatest awareness or appreciation of clear cabin air. Beyond that, there appears to be little understanding of the issue in the absence of any useful consumer information.
To help address this, Emissions Analytics is actively involved in a group aiming to standardise the measurement methodology for in-cabin pollution¹⁰. The group was initiated by the AIR Alliance, which already publishes ratings for tailpipe pollution¹¹. Along with Emissions Analytics, the group includes a number of vehicle manufacturers, academics, and filter and ventilation suppliers. Once completed, recognised and repeatable testing should enable ratings to be published that will both inform car buyers and, indirectly, incentivise manufacturers to improve interior air quality.
The Covid-19 pandemic brings these issues to the fore, as the virus is a particle of approximately 100nm in size. While ingress of live virus particles from outside into the vehicle is unlikely, reducing the chance of one infected occupant transmitting the virus to another is more relevant. Therefore, the rate at which air is recirculated and re-filtered matters. In this context many initiatives have appeared from vehicle manufacturers, suppliers and after-market companies. One example has been trailed by Jaguar Land Rover, using hydroxyl radicals to ‘purify’ cabin air¹². While this may be true in terms of neutralising a coronavirus, surplus hydroxyl radicals can also react to form toxic secondary oxygenated gases and aerosols¹³, and so it is vital to perform a broader, perhaps untargeted, assessment of the effects of such systems. Systems should be compared to the efficiency of filter-based systems such as on the Tesla X, to judge what value the hydroxyl radicals are adding – a judgement that will be allowed once there is a standardised method through CEN Workshop 103.
Thus, perhaps the future market for vehicles will be one of the quality of the experience rather than the magnitude of the performance. BEV range anxiety may be quelled and the charge-up infrastructure made omnipresent. Cheap, renewable energy will make efficiency almost irrelevant. The gradual strangulation of the road space for cars, combined with connectively between vehicles and automation thereof, may leave occupants stripped of the joy of the driving experience, but consequently more demanding in terms of the quality and healthiness of the experience. And this differentiation in experience, comfort, quality and design may be the route to profitability for manufacturers.
Footnotes:
https://www.emissionsanalytics.com/news/2020/1/28/tyres-not-tailpipe
PM2.5, i.e. all particles up to a diameter of 2.5μm
https://www.tesla.com/en_GB/blog/putting-tesla-hepa-filter-and-bioweapon-defense-mode-to-the-test
DPham, L., Molden, N., Boyle, S., Johnson, K. et al., “Development of a Standard Testing Method for Vehicle Cabin Air Quality Index,” SAE Int. J. Commer. Veh. 12(2):2019, doi:10.4271/02-12-02-0012