And yet, this misses the point. NOx emissions are only PART of the story. Particulate matters, and under driving conditions we constantly endure (stop-and-go), particulate is produced massively, with very small particle size. That, along with NOx, creates the massive smog in Europe and respiratory conditions. NOx may break down and all, but soot doesn't. One can justify, pointlessly IMHO, that diesel is still worth, but in all reality, particulate will kill it.