![]() To our surprise, in real-world testing we found that tyre wear can be much, much higher than our starting hypothesis – as shown in our previous newsletter. Quadrupling the figure to account for four tyres, and dividing by 320 gives a theoretical per km mass loss of 0.2g (200 milligrams), already 44 times more mass loss per kilometre than is permitted in the current exhaust regulation (4.5 mg/km). In respect of the 200-mile (320km) test we conducted, this equates 16g in mass loss over that distance. In our initial tyre testing we began with a basic mass loss approach, hypothesising that an average tyre might shed an estimated 1.5kgs over a 30,000km life. How to explain these figures, which seem inexplicably high? Non-exhaust emissions are believed to constitute today the majority source of primary PM from road transport, 60% of PM2.5 and 73% of PM10. While this has been going on, tyres have not been regulated at all for their emissions, and are believed to have become a leading source of non-exhaust emissions and of broad concern whether considered as an airborne source of pollution or as a watershed microplastic. This increase in ultrafines has only recently been policed with the introduction of the Real Driving Emissions regulation. If we are correct about this, there has been a sharp increase in potentially dangerous ultrafine particles as a consequence of the widespread adoption of direct injection gasoline engines plus a market swing back to gasoline. Upon the canister being opened, the particle number soared tenfold in the ambient air, but the corresponding exhaust count remained largely flat throughout the hour, with even a slightly declining trend. ![]() Emissions Analytics worked with the leading European automotive publisher, Auto Motor und Sport, to test four recent models of diesel cars.Ĭonsidering one of the vehicles, a canister of high intensity particles was opened in front of the air intake on four occasions across 60 minutes while the car idled. So long as this filter has not malfunctioned or been tampered with, emissions are low over typical driving cycles, even taking into account the significantly elevated levels during the periodic ‘regeneration’ of the filter where the accumulated particles are burned off.įilters are so good that we have measured that in certain circumstances, when the ambient air is already polluted, a diesel car will tend to extract more particles from the air than it emits. ![]() ![]() If we tackle diesel vehicles first, the truth is that they have emitted very few particles, at least in relative terms, since the broad introduction of diesel particulate filters a decade ago. In the light of this, we have begun a broad tyre testing programme at Emissions Analytics.Ĭomplementing this is our traditional expertise in exhaust emissions, which for the purpose of this newsletter will focus on diesel exhaust particulates and some further reflections on the particle emissions of gasoline engines.ĭeclining tailpipe emissions from diesels However, thanks to the high weight and poor aerodynamics of sport utility vehicles (SUVs) as well as the high weight and torque drive characteristics of battery electric cars (BEVs), tyre emissions are expected to increase. Greater adoption of regenerative braking means that brake wear emissions may decrease. Non-exhaust emissions include physical road wear particles from vehicles eroding the surface, the re-suspension of existing particles lying on the carriageway, brake wear particles and tyre wear particles. The 2019 report Non-Exhaust Emissions from Road Traffic by the UK Government’s Air Quality Expert Group (AQEG) recommends “…as an immediate priority that non-exhaust emissions (NEEs) are recognised as a source of ambient concentrations of airborne PM, even for vehicles with zero exhaust emissions of particles.”
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