Last time I talked about using carbonic acid from flue gases to neutralize an alkali solution. With a little research i realized nitric acid is much more suited for this.
Nitric acid is a strong acid even considering the soluability of NO2 in water (where CO2 is not very soluable). Thus it can fully neutralize and acidify an alkali solution. Alkali nitrate salts are pretty soluable, and can be easily washed from a precipitate. And, Alkali nitrate salts are not very stable, decomposing much more easily from heat than carbonates.
Nitric acid is the result of high temperature combustion (>1500C) or of burning nitrogen containing fuel, especially with a rich mixture of oxygen. Thus not much of it would be found in destructive distillation exhaust, but much more from oxygen enriched metal working processes. More about the formation of NO2 in the last couple paragraphs of this paper (http://www.nfcrc.uci.edu/EnergyTutorial/combustion.html)