There is good news from a historical perspective, even during a point and time when this beautiful earth supported the largest o2 breathing animals walking around in history, the "air quality" was much worse in the terms that most people today are hysterical about. It turns out the burning of fossil fuels doesn't even move the needle when you look at a historical perspective and earths health. Today the co2 levels are right where the lowest co2 levels are in the historical graph, today between 400-500ppm. The good news is in 60 years or so, mankind will have to find something different to be hysterical about because fossil fuels will be gone.
My apologies for using the word liberal, I was really just laughing at DEF as a solution to save us.
If you were worried about n2o, despite all of the use of diesel without DEF, As of 2010 pre DEF, it was estimated that about 29.5 million tonnes of N 2O (containing 18.8 million tonnes of nitrogen) were entering the atmosphere each year; of which 64% were natural, and 36% due to human activity. So once again, follicle fuels will be gone soon enough, but the air quality will not change much in any sort or fashion. Meanwhile, I just had a friend lose his job of delivering trusses because the owner couldn't afford the DEF conversion of his fleet. Lots of pain and loss for something that wont even show up in the blip of history. They had 3 trucks and an additional machine that needed to be retrofitted, the owner could only afford 1 truck. Most of his employees were fired, despite his trucks bought new in 2004/5.