I have a car built in the 1980s and its gear ratios are built for fuel economy. I can't race away from a stoplight in it, but I get better fuel economy. Engine manufacturers have been working very hard to make the diesel engine clean. The industry is still, however, challenged by the problem of emissions. Gasoline engines make hydrocarbons, but these can be burned with a catalytic reactor.
Particulates are much harder to eliminate.
Particulate traps, basically filters, are being used in some applications to prevent PM emissions. Plasma reactors are also being considered as a possible solution. The problem with these approaches is that the equipment is bulky and consumes energy. The ideal approach is to prevent PM from forming during the combustion process. There have been several approaches through changes in fuel chemistry.