Why are BEVs not required to meet air quality laws in Europe? Since the introduction of the Real Driving Emissions (RDE) on-road validation of certification values introduced mid-way through Euro 6,gaseous tailpipe pollutant levels are now confirmed as low in average driving. For some, they were low even before RDE. The average nitrogen oxide (NOx) emissions from RDE diesel vehicles are 45mg/km and falling, compared to the regulatory limit of 80mg/km. Mean carbon monoxide from RDE gasoline vehicles is 157mg/km compared to the limit of 500mg/km. Total hydrocarbons (THC) from RDE gasoline vehicles are now typically below 10mg/km compared to the limit of 100mg/km. Particle mass emissions are now very close to zero on current diesel and direct injection gasoline vehicles, with a limit of 4.5mg/km on the PMP procedure.
Of the regulated pollutants, therefore, all seem well controlled, except for ultrafine particle emissions – measured through the particle number (PN) standard – and potentially particles more generally from port fuel injection gasoline cars. The widening of the size range of particles measured, down to 10nm, likely to be proposed in Euro 7, will offer a valuable tightening of this part of the regulatory regime.
For the Euro regulations themselves, greenhouse gases are not regulated – except indirectly for methane (CH4) through THC – as the fleet average carbon dioxide (CO2) targets act separately. Whether promoting BEVs is the optimal way to achieve these targets was the subject of a previous newsletter. Relevant here is the potential addition of methane and nitrous oxide (N2O) under Euro 7, even though they are primarily greenhouse gases rather than air quality pollutants. They are both more potent greenhouse gases than CO2, although survive for a shorter time in the atmosphere: 28 and 265 times higher potency respectively on a hundred-year time horizon1. Therefore, only small amounts of N2O emissions could nullify much of the hard-won CO2 reduction.
So, on the surface of it, Euro 7 could be the last regulation for pollutant emissions, while greenhouse gases are actively addressed through the CO2 targets. What may be neglected, however, is volatile organic compounds (VOCs) from the exhaust. These compounds are numerous, small in volume but potentially highly toxic in their human health effects. Therefore, their current regulation in the laboratory as non-methane hydrocarbons (NMHC) may be insufficient: not only that the limit is high at 68mg/km, but also that it does not apply to diesel vehicles. Furthermore, by only considering the total, there is no visibility on whether that total is made up of toxic or innocuous compounds.
The University of York in the UK has been at the forefront of studying this area, highlighting particularly the role of these compounds in the atmospheric chemistry that leads to ground-level ozone and secondary organic aerosol particle formation2. Therefore, these compounds do not just have direct effects on human health, but indirectly lead to poor air quality. While oxidation catalysts in the exhaust of gasoline vehicles may be highly effective in converting VOCs, their effectiveness against the heavier, semi-volatile organic compounds (SVOCs) such as the carcinogenic polycyclic aromatic hydrocarbons (PAHs) is less clear. Generally, also, these ICE vehicles suffer from relatively high VOC and SVOC emissions when the engine is cold.
From this, we can conclude that Euro 7 perhaps should not be the final regulatory stage, so long as ICEs are still sold, which is likely to be through to at least 2035 in Europe. While Euro 7 is looking at regulating a small number of highly volatile compounds such as formaldehyde, the broader spectrum of organic compounds is not currently being actively considered. This is important when you put it in the broader picture of the environmental impact of vehicles. Specifically, there are instructive parallels with the emissions from tyres and from materials inside the vehicle cabin – both of which are very lightly regulated currently. Tyres will be a topic of a later newsletter, so here we will focus on the vehicle interior.
In our last newsletter, we reviewed the evidence for concentrations of particles and CO2 in the cabin during on-road driving. It concluded that the quality of air inside the cabin is highly dependent on the quality of the ventilation system and its filter. For some vehicles, in-cabin particle concentrations were many times higher than outside on average, and the use of the recirculation mode led to steep rises in CO2 concentrations to the point of potentially having cognitive effects on the driver.
But that is not everything. The single biggest complaint from new car buyers in China is about the ‘new car smell’, which is caused by a mix of VOCs. These VOCs may have health effects that go well beyond simply causing malodours. The source of the new car smell is VOCs being released from interior materials and glues used to put the vehicle together. Sources of VOCs go beyond that too, including those that enter the cabin from outside (which in turn come from other vehicles, home heating, industrial sources and so on), fuel evaporating from the tank and emissions from the body and clothing of human occupants. What is important is to be able to differentiate the toxic from the harmless VOCs – the toxic ones being more likely to come from combustion of fossil fuels or materials derived from fossil fuels, such as plastics and adhesives.
To study this, Emissions Analytics has recently opened a testing laboratory with two-dimensional gas chromatography and time-of-flight mass spectrometry from Markes International and Sepsolve. This allows us to test for tailpipe and in-cabin VOCs with excellent separation, identification and quantification. Taking one of the early car tests, a sample of air was taken and 617 different compounds were identified, with 25 being particularly being abundant. These compounds can be illustrated on a two-dimensional chromatogram, as shown below. The horizontal dimensions are the two axes of separation and each peak represents one compound, with the area under the peak broadly reflecting the amount present.