I’m guessing CO2 that didn’t undergo conversion? Or the non-CO2 gases (comprising ~5% of the Martian atmosphere) that made it into the system and thus weren’t a

I’m guessing CO2 that didn’t undergo conversion? Or the non-CO2 gases (comprising ~5% of the Martian atmosphere) that made it into the system and thus weren’t affected? Or the CO byproduct that wasn’t expelled separately? Edit: thinking about the numbers some, I think non-CO2 (Martian!) atmospheric gases is a good guess for the bulk because they’re 5% of the atmosphere and the conversion input is two CO2 for one O2 out, so at the 2:1 ratio with 0.95 of the input converted you end up with 98.96% converted to either O2 or CO, and the rest is whatever else you had mixed in there, if I did the math right. Depending on how the O2 and CO are separated, the non-CO2 gases not affected by the conversion/reaction could plausibly end up all with the O2, all with the CO, or some mix of the two (probably by weight?). Add in a few ppm of CO2 that slipped through the process unconverted and Bob’s your uncle. Maybe.