Why there is sudden rise in pollution in Delhi: Temperature inversion ?

Everybody is aware of the 'Kadwi Hawa' of Delhi but what makes the air pollution situation in Delhi worse? We all know that industrial emissions, vehicle exhaust, construction activity, etc, are the biggest contributors to pollution in Delhi throughout the whole year, but the situation specifically gets worse during winter months. What aggravates the already bad situation?

Major contributing factors to Delhi's pollution are:

  • Inversion: Usually the temperature in the atmosphere decreases with height, hence warmer air close to the earth's surface moves upwards and the air does not get stagnant. However, during inversion cold air gets trapped close to the surface overlain by a layer of warm air. This phenomenon cap the movement of air.
  • Wind pattern: In winter 72 % of the wind blows into Delhi from the northwestern part of India and Pakistan, these winds are not too strong during the monsoon season. This wind brings particulate matter along with it.
  • Stubble burning: After harvesting paddy, there is some leftover on the ground which is called stubble. Farmers in Punjab and Haryana burn the stubble left out after harvesting the crops which is the biggest contributor(70 percent) to the deterioration of air quality in Delhi. This stubble could be disposed of effectively by using machines, but these machines do not come for nothing. Farmers choose not to invest in these machines and simply burn the stubble. 
  • Industrial hubs: It is significant to mention that adjoining areas of Delhi are the industrial hubs therefore it probably results in the inflow of a mixture of coarse and fine continental pollutant aerosols.
The sudden increase in pollution is attributed to the coincidence of all these factors. Stubble burning is followed by the northwestern winds blowing into Delhi. These winds bring with them smoke caused by stubble burning, and the pollution from industry. These all are assisted by the phenomena of inversion, which makes this toxic gas stagnant, and the city gets choked. 

This all happens usually at the onset of winter because at this time temperature is not sufficiently low to condense the water vapor and not sufficiently high to evaporate it. It is at that temperature at it just traps the particulate matter and remains suspended in the atmosphere.


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