Step 1: Understanding the Concept:
Total column ozone refers to the total amount of ozone in a vertical column of air stretching from the Earth's surface to the top of the atmosphere.
Step 2: Detailed Explanation:
The Dobson Unit (DU) is the standard measurement unit.
One Dobson Unit is defined as the thickness of a layer of pure ozone that would be formed if all the ozone in the column were compressed to standard temperature ($0^{\circ}$C) and pressure (1 atm).
Specifically, 1 DU = 0.01 mm thickness of pure ozone at STP.
The average total column ozone is about 300 DU (which would be 3 mm thick).
Step 3: Final Answer:
The standard unit for Total Column Ozone is the Dobson Unit.