Dual hose AC and CO2

So I got a new dual hose AC unit. So far works great. I have noticed that the CO2 level does seem to dip when the AC is on (from like 800 ppm to 600 ppm). I'm thinking maybe even though there is an intake hose perhaps some air is being exhausted out. Or perhaps CO2 is being "filtered" out (if that makes any sense)? Any else with CO2 and dual hose noticed this?