What is CO2 measured in?

CO2 can be measured in several different ways. It can be measured as a partial pressure of total gas (i.e. it's contributory percentage of total air pressure) usually in millimeters of mercury (mm Hg). This measure would be used more by medical sciences in a blood gas analysis. It can be measured in parts per million (how may parts of a million representative air sample that are CO2 particles). This measurement would be widely used in environmental sciences. It is typically measured by weight if it is frozen for commercial and industrial situations.