Perhaps it’s mostly existing particles laying on the road that are thrown up by the next vehicle’s tyres as it passes?
Resuspension of road dust is literally one of the 4 things they defined as the NEE they're measuring.
But counting "resuspended road dust" as "emissions" seems pretty far fetched to me. Especially if that's a significant portion of the "5.8 grams per kilometer of particles", and you then push out a press release with the hyperbolic headline claim "Pollution from tire wear 1000 times worse than exhaust emissions."
And they then have the audacity to claim: "Emissions Analytics seeks to bring transparency to a confused market sector."
Pretty sure I know who's funding them now, without even bothering to google it...
(But if it _is_ the Hovercraft Lobby, I'm totally in!)