Don't you guys think that the C02 will come OUT of solution as it's being applied and then be given up to the atmosphere? Without metering how do you know this does anything at all?
Seriously, without metrics experimentation is mostly useless. Or at least, without metrics your experimentation is far from scientific and therefore isn't really solid as a foundation for any sort of assumptions.
That being said, when you pour the carbonated water into the spray bottle it will release a lot of the carbonation. When you force the solution through the spray nozzle and atomize the solution, wouldn't all the carbon be released? I am sure /some/ would still be in there, but would it be in the form of CO2? I doubt it.
Still, it's possible that the release of the carbonation into the room would augment the CO2 levels. In which case, you might as well just set a glass full of soda water behind your fan and hope that it adds CO2 to the ambient atmosphere as it naturally releases its carbons more slowly.
Not something I'm rushing out to try though. I'm more likely to pick up some dry ice before I start leaving soda water lying around my grow.