Dobson unit
Also called: DU · Topic: Atmosphere: Composition, Structure and Elements of Weather · NCERT: Beyond NCERT
Meaning
The Dobson unit (DU) measures the total amount of ozone in a column of air from the ground to the top of the atmosphere. 1 DU equals a layer of pure ozone 0.01 mm thick at standard temperature and pressure. The global average is about 300 DU. If all that ozone were squeezed together at the surface, it would make a layer only about 3 mm thick. An ozone hole is an area where ozone falls below 220 DU.
Example
Every spring (September–October), ozone over Antarctica drops below 220 DU, forming the ozone hole. Over most of the world, including India, values stay near the 300 DU average.
Don't confuse with
- ppm (parts per million): ppm gives a gas's share of the air, like CO2 at over 420 ppm. The DU gives the total thickness of ozone in a whole column of air.
Related concepts
- Ozone layer
- Ozone hole
- Polar stratospheric clouds
- Montreal Protocol
- Kigali Amendment
- Stratospheric aerosol injection