[bradlys]

It's mostly for bikes before Euro4/5. Obviously, new bikes are one thing but most bikes in the USA are offenders of pollution.

A statistic for CA was motorcycles make up 1% of my miles driven but 10% of smog pollutants.

[kube-system]

Bikes didn't require catalysts for a long time. And they often used less-precise fueling systems, like carburetors. But that has changed or is changing in a lot of places more recently.