General Science question from Naib Tehsildar exam, 2018 by JKSSB
What is the unit of measurement for the total amount of ozone in the atmosphere above a point on the earth’s surface?
Last updated May 13, 2026
Correct Answer:
Option A —
Dobson Unit
What is a Dobson Unit?
The Dobson Unit is the most common way to measure the concentration of ozone in the atmosphere. It represents how thick the ozone layer would be if all of the ozone molecules in a column of air were brought down to the Earth's surface at standard temperature and pressure (0°C and 1 atmosphere of pressure).
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The Measurement: One Dobson Unit is equivalent to a layer of pure ozone only 0.01 millimeters thick.
A "Healthy" Layer: A typical ozone layer has a concentration of about 300 Dobson Units. This means if you compressed it all, it would only be about 3 millimeters thick—roughly the thickness of two pennies stacked together!
Why the other options are incorrect:
Darson Unit: This is not a recognized scientific unit of measurement for ozone.
Datsun Unit: Datsun is actually a famous brand of Japanese automobiles, not a scientific unit.
Dalton Unit: A Dalton (Da) is a unit of mass used to express atomic and molecular weights (also known as the unified atomic mass unit).
The Origin
The unit is named after G.M.B. Dobson, a British physicist and meteorologist who, in the 1920s, built the first instrument (the Dobson spectrophotometer) to measure total ozone from the ground.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
