In some cases, the NOx can be eliminated at the source. If formed from the HNO3, as when used for stripping plating, add a bit of H2O2 to the nitric stripping solution. The H2O2 catalyzes the reaction of NOx back to HNO3 before it ever leaves the solution. This conserves HNO3 as well as eliminates the NOx.
Only 0.1-0.2 vol% H2O2 (49 wt%) is required for heavy stripping; e.g., when using 50 vol% nitric on electroless nickel plated out on an SS HXer. Works well at ambient temperature; at some higher temperature the H2O2 will decompose too rapidly to be practical.
Of course, this tip is for end-users, not equipment manufacturers. If the latter, you could perhaps earn some customer good-will with this tip. It's not generally known; I've met EN platers with 15 & 20 years experience who were really grateful to get rid of the red-orange fumes.