I’m wondering if it's more to do with diesel passenger vehicles.

You have to work really hard to even find a diesel passenger car in the States. Whereas, at least for right now, they’re ubiquitous in the EU. (I mean an every day consumer vehicle you buy at a car dealership, ranging from a hatchback to an SUV.)

Which was ostensibly good for carbon emissions, given the fuel efficiency of contemporary diesel engines. Except, oops, they were lying through their teeth about non-CO2 emissions, and they kick out a godawful amount of pollution.

Right. Diesel is filthy and thankfully never became very popular in the US except for tractor/trailers and railroads.

I believe wood burning fires and trash fires also contribute.

Hence my comment tying soot to population density.

And to check myself…

https://www.dieselforum.org/diesel-drivers/clean-diesel-vehi...

Yup, outside of heavy-duty body-on-frame trucks and SUVs, they are gone now.

Although I swore the Mazda CX-5 had a diesel option…

> outside of heavy-duty body-on-frame trucks and SUVs

But aren’t the best selling cars in the US exactly heavy-duty body-on-frame trucks and SUVs?

The most popular car in the US for the last 30 years is the F-150.

Yes…but even in that class, they sell a teeny, tiny percentage as diesels.

https://www.dieselforum.org/vehiclesales/u-s-vehicle-sales-d...

And though I cannot find a citation, I swear I have heard the best-selling F-150 engine is the turbocharged gasoline V6.

Diesel is definitely part of the story. High fuel taxes in the EU help lead to more diesel given their superior fuel efficiency. But more diesels mean more particulate matter.

I didn't realize this until 10 years after I started feeling these feelings, but diesel exhaust elicits a strong feeling of nostalgia in me from my travels throughout Europe. I would be occasionally reminded of it in the United States but I never knew what it was until I stood next to an idling 18 wheeler

Diesel exhaust smells like ice cream to me. I assume it's an association from diesel ice cream vans as a kid.

I have similar association between bottled propane smell and cotton candy — cotton candy vendors around here used gas powered machines, which must have leaked during operation.

I have the exact same nostalgia from that smell, although I was fortunate enough to know what it was at the time (“exhaust” not diesel specifically).

Sigh, oh, that lovely passage in Proust’s In Search of Lost Time when he writes of diesel exhaust…

Those countries do have higher population density, but air quality in US cities is still better than air quality in European cities.

Mongolia is probably not the exampke you are looking for... https://www.nationalgeographic.com/environment/2019/03/mongo...

Ha, good point! But I imagine they still have very low overall soot pollution when averaged over the entire country. Who knows... but thanks for educating me.

Which actually makes it worse from a human perspective, since there are more people there to actually breathe in that particulate matter.