The thickness of the ozone layer is measured in ______.
- (a)Ångström
- (b)Dobson Unit
- (c)PPB
- (d)PPM
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'.
- (a)Ångström — 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)PPB — 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)PPM — Parts-per-million is also a concentration ratio (e.g., used for CO2 levels), not the column-thickness measure that Dobson Units capture.
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.
Exams pair this with other 'match the quantity to its unit' facts (radioactivity in becquerel, sound in decibel). Anchor it as: ozone LAYER THICKNESS/COLUMN = Dobson Unit.
- Ozone layer thickness/column amount is measured in Dobson Units (DU), named after G.M.B. Dobson.
- 1 Dobson Unit corresponds to a 0.01 mm thick layer of pure ozone gas if compressed to standard temperature and pressure.
- Typical global column ozone is roughly 300 DU; values fall sharply in the Antarctic ozone hole.
- Ångström measures wavelength/atomic-scale length; PPM/PPB measure trace-gas concentration — both are different kinds of quantities from a Dobson Unit.
Ozone's total column thickness is reported in Dobson Units — not ppm/ppb, which measure concentration rather than column thickness.
- Confusing ozone's column-thickness unit (Dobson Unit) with a concentration unit (ppm/ppb) — they measure different things.
- Mixing up 'ozone as protective layer' (stratosphere) with 'ozone as pollutant' (ground-level smog) contexts.
MPPSC and UPSC both like direct 'X is measured in which unit' questions for environment/atmosphere topics — lock unit-to-quantity pairs precisely.
No directly related past PYQ was found (a matching prior question exists but isn't attemptable yet).
- practice — not a real PYQ
The Dobson Unit is used to measure:
- (a)Radioactivity
- (b)Sound intensity
- (c)Atmospheric ozone column thickness
- (d)Wavelength of light
Answer(c) Atmospheric ozone column thickness.
- practice — not a real PYQ
Which international agreement is most directly associated with phasing out ozone-depleting substances such as CFCs?
- (a)Kyoto Protocol
- (b)Montreal Protocol
- (c)Paris Agreement
- (d)Basel Convention
Answer(b) Montreal Protocol — the treaty specifically targeting ozone-depleting substances.