In early 2020, UK-based independent testing firm Emissions Analytics published a study claiming that tire particulate wear emissions were 1,000 times worse than exhaust emissions (earlier post). Since that study, which was transparently designed to quantify the worst-case tire emissions under legal driving, Emissions Analytics has been testing and analyzing tire wear emissions in more detail across a wider range of driving conditions, and has performed a detailed chemical analysis of hundreds of new tires.
The company has also worked with the National Physical Laboratory in the UK objectively to quantify the uncertainties in the measurements of chemical composition.
Emissions Analytics now concludes that, comparing real-world tailpipe particulate mass emissions to tire wear emissions, both in ‘normal’ driving, the latter is actually around 1,850 times greater than the former.
Quoting such ratios, however, needs careful interpretation. The fundamental trends that drive this ratio are: tailpipe particulate emissions are much lower on new cars, and tire wear emissions increase with vehicle mass and aggressiveness of driving style. Tailpipe emissions are falling over time, as exhaust filters become more efficient and with the prospect of extending the measurement of particulates under the potential future Euro 7 regulation, while tire wear emissions are rising as vehicles become heavier and added power and torque is placed at the driver’s disposal. On current trends, the ratio may well continue to increase.
—Emissions Analytics. . . .
The company notes that an important difference between tire and tailpipe particle emissions is that most of the former go straight to soil and water, whereas most of the latter is suspended in air for a period, and therefore negatively affects air quality. Emissions Analytics’ results suggest around 11% of the mass of tire emissions is smaller than 2.5 microns in diameter (defining the common metric for fine particle dust, PM2.5, which can be airborne). Therefore, the airborne tire emissions are more likely to be around 8 mg/km—this is still more than 400 times higher than tailpipe emissions.
Considering just tire mass emissions may underestimate the effect on air quality and the consequent human health effects, the company said. The particulate number can be estimated, as shown in the table below. . . . .
There's a whole lot more detail. The obvious question that comes to mind is this. As PEVs especially BEVs are considerably heavier than ICEs, how much of a net improvement if any in (particulate) emissions is there when switching from ICEs to PEVs? They did measurements with an additional vehicle mass of 500kg to see what effect that had. Note, they're not talking about GHGs, just particulates.