Minor nitpick, but tailpipes aren't the primary source of emissions. The study is about PM2.5[0]. which will chiefly be tires and brake pads. Modern gasoline engines are relatively clean, outside of CO2, though diesel engines spit out a bunch of bad stuff.
Exactly. The noxious tailpipe emissions in a city are usually from diesel trucks, small vehicles like motorcycles (small or absent catalytic converters), modified vehicles (catalytic converter removed or diesel reprogrammed to smoke), but not modern gasoline ICE vehicles.
The love for diesel engines in many European countries was always confusing to me.
PM2.5 is also a broad category of particulates that come from many sources. The PM2.5 levels in the air depend on many sources, with wind being a major factor in changing PM2.5 levels. It’s hard to draw conclusions when a number depends on the weather and a lot of other inputs.
https://en.wikipedia.org/wiki/Volkswagen_emissions_scandal
When you remove the cheating and give adequate weight to those emissions, diesel for passenger vehicles makes a lot less sense.
The focus has more recently shifted to reducing overall emissions of CO2 and other harmful gases and particulates, which makes diesel much less appealing.
I suspect that modern (last five years) turbocharged gasoline engines are probably approaching diesel thermal efficiency, but I don't think that it's correct to say that they generally surpass it. The gasoline Ford EcoBoost is 33% thermally efficient while a BMW N47 turbo-diesel is 42% thermally efficient, as an example [2].
[1] https://afdc.energy.gov/fuels/properties [2] https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...