'Ozone layer' absorbing ultra-violet radiation exists in which of the atmospheric layer?
- (a)Troposphere
- (b)Mesosphere
- (c)Thermosphere
- (d)Stratosphere
Correct — D, Stratosphere. The ozone layer lies in the lower-to-middle stratosphere, roughly 15-35 km above the surface. There, ozone (O3) absorbs most of the Sun's harmful ultraviolet (UV-B and UV-C) radiation. This absorption also warms the stratosphere, so its temperature rises with height (a temperature inversion). This UV-shielding by stratospheric ozone is what makes complex life on Earth possible.
- (a)Troposphere — The troposphere (0 to about 12 km) is the lowest layer, where weather occurs; the protective ozone layer sits above it in the stratosphere. Ozone at ground level here is a pollutant, not the shielding ozone layer.
- (b)Mesosphere — The mesosphere (about 50-85 km) lies above the ozone layer and is where meteors burn up; it is not where the ozone layer is concentrated.
- (c)Thermosphere — The thermosphere (about 85-600 km) contains the ionosphere and auroras; it is far above the stratospheric ozone layer.
Earth's atmosphere is layered by its temperature profile: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The stratosphere contains the ozone layer, which absorbs solar UV radiation. Because absorbing UV heats it, the stratosphere's temperature increases with altitude — making it stable and cloud-free, which is why jet aircraft prefer to cruise there.
Students confuse 'ozone as a pollutant' (harmful ground-level ozone in the troposphere) with the 'ozone layer' (beneficial, in the stratosphere). The question specifically names the UV-absorbing ozone layer, which is unambiguously in the stratosphere.
- The ozone layer lies in the stratosphere, roughly 15-35 km altitude.
- It absorbs harmful ultraviolet (UV-B, UV-C) radiation from the Sun.
- UV absorption warms the stratosphere — its temperature rises with height.
- Atmospheric order upward: troposphere then stratosphere then mesosphere then thermosphere then exosphere.
The ozone layer sits in the stratosphere (~15-35 km), absorbing harmful ultraviolet radiation.
- Mixing up 'bad' ground-level ozone (troposphere) with the 'good' ozone layer (stratosphere).
- Placing the ozone layer in the mesosphere or thermosphere simply because those layers are higher up.
UPSC/UPPSC ask which atmospheric layer hosts a given feature (ozone layer, ionosphere, weather) and why the stratosphere is stable and warms with height.
The formation of ozone hole in the Antarctic region has been a cause of concern. What could be the reason for the formation of this hole?
- (a) Presence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
- (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
- (c) Absence of polar front and stratospheric clouds; and inflow of methane and chlorofluorocarbons
- (d) Increased temperature at polar region due to global warming
Answer(b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
Same stratospheric-ozone concept — the ozone layer lives in the stratosphere, and its Antarctic 'hole' forms there when polar stratospheric clouds and CFCs destroy ozone.
- practice — not a real PYQ
In which atmospheric layer does temperature increase with height due to absorption of ultraviolet radiation?
- (a)Troposphere
- (b)Stratosphere
- (c)Mesosphere
- (d)Exosphere
Answer(b) Stratosphere — the ozone layer's UV absorption warms it, so temperature rises with altitude.
- practice — not a real PYQ
The Montreal Protocol is associated with the control of:
- (a)Greenhouse gases
- (b)Ozone-depleting substances
- (c)Persistent organic pollutants
- (d)Wetlands
Answer(b) Ozone-depleting substances — the Montreal Protocol (1987) phases out CFCs and similar chemicals.