The North Indian Haze

The North Indian Haze

  • The thick haze that has enveloped Delhi and surrounding areas is smog.
  • Smog occurs in a location that is far away from the actual source of pollution.
  • It is a result of various factors:
  1. Geography of the place
  2. Sunlight
  3. Calmness of winds
  4. Post-harvest crop burning
  5. Firing of brick kilns
  6. Pollution emitted by vehicles
  7. Industrial activity
  • The processes that lead to smog usually take place after the hazardous pollutants have drifted away in the wind.
  • In Delhi, there are two winds:
  1. One carrying pollutants from stubble burning in Punjab
  2. Other bringing in moisture from Uttar Pradesh
  • The two winds are colliding above the national capital and this combined with the near-still wind conditions near the ground level, have effectively trapped the pollutants, leading to the smog.
  • In Delhi, the ground-level ozone and PM 2.5 play the most significant role in formation of smog.



How is smog different from fog?


  • Fog is just the condensed water vapour that lies close to the ground.
  • When water vapour saturates the air, the vapour starts to condense back into a liquid, as water droplets.
  • These droplets, suspended in the air, appear as the thick haze that is known as fog.


  • When the pollution is high, nitrogen oxides and dust particles interact with sunlight to form ground-level ozone, leading to the building up of haze.
  • This haze is smog- a result of a photochemical reaction of sunlight with pollutants that have been released into the atmosphere.


What are these pollutants?

  • WHO classifies particulate matter into two broad types:
  1. PM10
  2. PM2.5
  • The numbers indicate the diameter of the particles in microns.
  • The major components of these particulate matters are- sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water.


How harmful is it?

  • The Indian Medical Association has termed this smog has “medical emergency” and it says that this air can be equated to smoking 50 cigarettes a day.
  • The most common symptoms of smog impact are: breathlessness, watering of the eyes and nose, burning sensation in the eyes, coughing, dizziness, headache and lethargy.
  • The most vulnerable groups include newborns, children, pregnant woman and those with pre-existing health conditions such as asthma, chronic bronchitis, diabetes and cardiac diseases.
  • There is evidence that high pollution can lead to premature birth, make pregnant women prone to miscarriage and cause foetal growth problems and lethargy.
  • Chronic exposure to both PM10 and PM2.5 can lead to the risk of developing cardiovascular and respiratory diseases, as well as of lung cancer.
  • Both of these matters can penetrate and lodge deep inside the lungs and PM2.5 can cross into the blood, causing damage in many organ systems.
  • Higher levels of nitrogen dioxide precipitate asthma; higher levels of sulphur dioxide precipitate chronic bronchitis.
  • There has been evidence that PM2.5 can also enter the bloodstream, and prolonged exposure can cause cause inflammation of heart arteries
  •  It can lead to thrombosis- when clotting inside a blood vessel obstructs the flow of blood and can atherosclerosis (A condition in which the diameter of blood vessels is reduced) and can result in hypertension.
Section : Environment & Ecology