[Kepler11110]

3 CH₄(g) + 4 N₂(g)  C₃N₄(s) + 4 NH₃(g)

I am assuming that the atmosphere is composed mostly of N₂ and the oxidation numbers for Nitrogen(±3) and Carbon(±4) so by substitution reaction I allowed C = +4, and N = -3 ... I think farts smell because of the Ammonia on the RHS of the equation...and not the Carbon Nitrate (C₃N₄)(s) that is the brown stain....

[AWK]

Formally all is OK. But did you check how much energy you need for this reaction?
Carbon nitride (not nitrate) is a very promising photoelectronic material but its synthesis is much more difficult so far.