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What is smog and how dangerous can it be?

Topics Covered: Pollution and conservation related issues.

What is smog and how dangerous can it be?


Smog in Delhi due to high levels of pollution.

  • This year, Delhi’s air pollution in October was higher in comparison to last year.

What is Smog?

Smog is a harmful mixture of fog, dust and air pollutants such as nitrogen oxides, volatile organic compounds, etc. which combine with sunlight to form a dense layer of ground-level ozone.

  • Ozone present high in the atmosphere is good, but when nearer to the ground, it can cause irritating health effects.

(Note: The term ‘smog’ was first coined by Dr Henry Antoine des Voeux in his paper, Fog and Smoke, in July 1905, after a blanket of smoke and fog was noticed over London in the early 1900s.)

How is Smog formed?

It consists of ozone, along with harmful substances like sulphur dioxide, nitrogen dioxide, carbon monoxide and PM10s, which can find their way deep into our lungs.

Smog can be caused by:

  1. Large amounts of coal-burning in an area
  2. Slash-and-burning of crops (a major source in Delhi)
  3. Smog-forming pollutants generate from automobile exhausts, power plants, fireworks, even paint, hairspray, charcoal starter fluid, and plastic popcorn packaging.

Role of local weather phenomenon:

The formation of smog is also closely linked with temperature, sunshine, and calm winds. On a warmer day, smog can form more quickly than otherwise.


Sulfurous smog and photochemical smog are two distinct types of smog recognised so far.

Sulfurous smog, also known as London smog, develops due to high concentration of sulfur oxides in the air.

Photochemical smog is produced when sunlight reacts with oxides of nitrogen and at least one volatile organic compound (VOC) in the atmosphere.

Health impacts:

  1. Inhaling smog over a long span of time can inflame your breathing passage, much like cigarette smoking.
  2. Smog causes inflamed lungs, and inflamed lungs, in turn, secrete interleukin-6 which can cause blood clots in people, cardiac and respiratory disorders, leading to heart attacks or strokes.
  3. Smog can dry out the protective membranes of your nose and throat.
  4. It can jeopardize your body’s ability to resist infection, hence, increasing your susceptibility to illness.
  5. It can greatly decrease the UV radiation, leading to low production of important elements like Vitamin D.

Sources: the Hindu.