Lightning is "blamed" in classic creation theory for fixing nitrogen
(presumably in oxides, but I guess amine groups must have come from
somewhere), to go into the "soup". Nowadays, black/white smokers are
thought to play a pivotal role, although I have never seen any reports
of nitrous compunds being formed in the deep sea (lots of metals, lots
of heat, and plenty of sulphur though!).
I'd agree that air pollution probably introduces more N into rainwater for
the majority of us, although I think the effects of lightening are actually
quite general (the atmosphere is pretty good at mixing things).
Same with carbonic acid. It occurs naturally in rainwater, but is probably
becoming more common. Helped by nitric acid too! :-))
Richard
(ex-Gurkha Land Rover - oops wrong listserver. Lots of sundews, plenty
of baby VFts and a couple of SarraceniA)