Is there a point at which NOx is formed in wood combustion in high enough concentrations to require mitigation?
As you've stated the obvious answer for clean wood combustion is to get the gases hot enough (I believe I've read 1600F is sufficient) with enough excess oxygen to progress the reaction to completion, but does this eventually produce NOx like an internal combustion engine does?
If it does I would imagine mitigation of the NOx becomes difficult, gasoline engines have the advantage of constantly cycling between lean and rich combustion and by using a 3-way catalytic converter effectively convert NOx and the unburnt hydrocarbons and residuals to nothing more than N2, H20 and CO2. I would think wood combustion would be more like that of a diesel engine, which is always oxygen rich, removing the simple 3-way cat as a mitigation method, which then leads toward more complex systems like Urea and an SCR which is used on the current generation of diesel engines.
. Note NOx is just a short version for multiple nitrogen compounds, thus the "x" There is fuel bound NOx and thermal NOx. A good hot fast burn that minimizes NOx does cause an increase in NOx. If I was tuning a big biomass boiler with NOx limits I would need to deal with it but small sources are currently exempt. There are two types of NOx precursors, fuel bound and thermal. There is minimal nitrogen compounds in biomass fuel most of it is mixed in with combustion air. So fuel bound really does not factor in. Thermal is stickier, if the combustion zone is very hot, the nitrogen in the air starts to "burn" from N2 to NOx. It would be rare for wood stove but I think the Jetstream type units did produce some. The trick with big biomass boiler similar to oil or coal boiler is the mess with the combustion zone by lengthening it out so the the peak temps stay low but for a longer time. The general term is Low NOx burners for liquid fuels and even coal boilers use the term. On a biomass boiler, messing around with where the air gets introduced extends the combustion zone that is hot enough to burn CO farther up the boiler while keeping peak flame temp lower. If that does not work ammonia can be sprayed in at a certain temp above the combustion zone to convert the NOx back to Nitrogen. Its moderately effective but very dependent on operation of the boiler. If very strict limits are required (Mass used to require advanced NOx control on biomass power generators until they decided that biomass was bad fro power plants) then the boiler has to be equipped with Selective Catalytic Reduction catalyst. Within a certain range of temps if ammonia or urea is mixed into the flue gas upstream of the catalyst, the NOx is then converted to ammonia. They work really well but its a proverbial cork in the tailpipe and expensive to install and run due to the increased draft lost. If the controls are off a bit and they overdose the ammonia there is the distinct odor or cat urine that settles down in the surroundings. We put one on power boiler and I could smell cat p*ss on occasion when driving to plant. The regulators politely call it "ammonia slip". 
