Think about this through.The largest global source of NOx emission is that of fossil fuel burning, with a recent estimate of 33 Tg per year.
If we could stop burning fossil fuel all together, what will happen to NOx (or CO2) emission over the long term? and what will happen to their presence in the atmosphere?
It is not a simple question.
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Mod edit:
This thread was split from --
VW - not so "Clean Diesel"
http://forum.allaboutcircuits.com/threads/vw-not-so-clean-diesel.115588/