MCQ Detailed View

The ozone layer is a vital part of Earth’s atmosphere, located in the stratosphere. It absorbs harmful ultraviolet (UV) radiation from the Sun, protecting life on Earth. To assess the health of the ozone layer, scientists measure the quantity of ozone in a given column of air. The standard unit used for this measurement is the Dobson Unit (DU).

A Dobson Unit is defined as the number of ozone molecules in a column of air that would form a layer of pure ozone 0.01 millimeters thick at standard temperature and pressure if compressed to sea level. For example:

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  300 DU means that if all the ozone in a vertical column of atmosphere were compressed, it would form a 3 mm thick layer.

  
  


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  The normal ozone level over Earth’s surface typically ranges between 200 to 500 DU, depending on geographic location and season.

  
  

Other options given are incorrect:

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  Dalton: A unit used to measure atomic and molecular masses.

  
  


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  Coulomb: A unit of electric charge.

  
  


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  None: Not applicable because Dobson is the correct unit.

  
  

Monitoring ozone levels is crucial because depletion of the ozone layer can lead to increased UV radiation, which causes skin cancer, cataracts, and environmental damage. Instruments such as Dobson spectrophotometers and satellite sensors are used worldwide to measure ozone levels in Dobson Units and track ozone layer recovery under international environmental protocols.

Thus, the correct answer is Dobson, the universally recognized unit for measuring the quantity of ozone in the atmosphere.