The fraud reported here impacts CO₂ emissions, not particulates. Plenty more can be done to reduce CO₂ emissions through increased thermodynamic efficiency, hybrid drive trains, weight reduction, and drag reduction. We are nowhere near the extreme limits yet, it's just a question of cost effectiveness. Gasoline engines with modern emissions control systems already emit tiny amounts of particulates and other pollutants. Diesel engines are probably not going to be viable for light passenger vehicles much longer as the limits get stricter.