We are looking to produce a spray changes colour when it comes into contact with Carbon Dioxide. Ideally this would be colourless when sprayed, but become a visible "smoke" where carbon dioxide is present. Failing this, we are open to a white "smoke" that changes to coloured where Co2 is present. We have looked at the possibility of having Sodium hydroxide mixed with water and a PH indicator in an aerosol, but don't think this will work. We are liking "Dangers" comment "vented co2" in the thread https://www.physicsforums.com/showthread.php?t=230130 Is there a possibility we use something like a smoke/fog machine solution in an aresol that also contains a ph indicator that changes colour where Co2 is present? Many thanks in advance, Kirsty.