– Gasoline has its compression limits as for higher compressions, the pre-mixture explodes before the spark comes in and the motor “knocks” as the highest pressure of the heated gases is before the piston reaches its highest point. Bad for performance and bad for the motor’s life expectancy.
– Modern gasoline motors (at least in Europe) were increasing performance by increasing the compression and injecting the fuel, instead of pre-mixing. Result: particulates at 10-100 times that for modern diesel motors. They simply forgot (?) to test for it, until an independent lab did it for them. NOx still low as they use a stoichiometric mixture (just as much air as can be used by the fuel).