Diesel's weaknesses have more to do with the poor fuel quality that we have here in the states. Diesels are cleaner than gasses on HC, CO, and CO2 emissions without catalytic convertors. They are higher in particulates, NOx, and for now, SO2 emissions.

Despite the higher particulates, they are indeed heavier than the microscopic particulates emitted by gasoline engines, and do fall out of the atmosphere. Changes in fuel quality regulations will help correct the other issues with diesel engines. The new regs will also open the doors to add exhaust aftertreatments to further cut emissions.

Of course, no engine exhaust is good for you. What the environmentalists don't tell you is that gasoline exhaust contains all of the same cancer causing gunk in it that diesels are alleged to.