A 3L sample of urban air was bubbled through a solution containing 50ml of .0116M Ba(OH)2, which caused the CO2 in the sample to precipitate as BaCO3. The excess base was back-titrated to a phenolphthalein end point with 23.6ml of .0108 M HCl. What is the concentration of CO2 in the air in parts per million? use 1.98g/L for the density of CO2.