In New York City, congestion pricing leads to marked drop in pollution

I won't change my mind about emissions in NYC. NYC is full of modern, western cars.

Two-stroke engines are terrible, classic automobiles are terrible, cars with no emission regulations will tend to be terrible. Cars in NYC will have catalytic converters and other technologies to reduce tailpipe emissions.

western? what is this less polluting non-western car you are advocating?

They probably mean two stroke motorcycles.

The notable source of bad tailpipe emissions in NYC are heavy diesel trucks, which, to my understanding, produce a large proportion of tailpipe particulates (and NOx) in the US, despite being a small fraction of overall vehicles on the road. There are strong correlations with heavy truck traffic and asthma rates.

Unlike many other places in the United States, NYC area’s railroads are almost exclusively passenger rail and there is comparatively very little freight railroad traffic serving NYC and therefore there are way more trucks in NYC. They emit way dirtier emissions. The problem is never the cars; it’s always the trucks.

And oh also the small engines powering street food carts.

Pretty much any new car sold in the US, Canada, Mexico, and most of Europe. "Western" typically refers to "countries rich/developed enough to [in this case] add emissions regulations". It's a luxury that many countries haven't gotten to yet, but is widespread in North America and Europe.

The good news is that I believe Ho Chi Minh City is about to start, so hopefully they'll have much cleaner air in a couple years.

Yeah, my neighbor at my last place had a diesel pickup and I could both hear and smell that it was diesel whenever he started it up.

My bad. Your original post did not imply NYC nor did it exclude motorbike engines. It was very general.