The thickness of the ozone layer is measured in ______.

Question

UnlockIAS · Accepted Answer

Correct — B, Dobson Unit (DU). The total column of atmospheric ozone — how much ozone lies in a vertical column of air, not its local concentration — is conventionally reported in Dobson Units, named after G.M.B. Dobson, a pioneer of ground-based ozone measurement. Typical total-column ozone readings are around 300 DU, and they drop sharply over the Antarctic 'ozone hole'.

Why the other options are wrong — (a) Ångström is a unit of length (used for wavelengths of light and atomic-scale distances), not a measure of the ozone layer's column thickness.  (c) Parts-per-billion is a unit of trace-gas concentration (a mixing ratio), a different kind of quantity from the ozone layer's total column thickness.  (d) Parts-per-million is also a concentration ratio (e.g., used for CO2 levels), not the column-thickness measure that Dobson Units capture.

Concept: Ozone (O3) in the stratosphere is reported as a 'column' measurement — the total amount of ozone found in a vertical column of air above a point on Earth — expressed in Dobson Units (DU), rather than as a simple concentration ratio like ppm or ppb.

State PCS 2024 Q5 — Geography PYQ with Answer

State PCS 2024 Q5 — Geography PYQ with Answer