AIR POLLUTION

Subject: Environment

Context : Every year in October, Delhi’s air quality starts to dip and a war of words between different governments erupts.

Concept :

• Air pollution in Delhi and the whole of the Indo Gangetic Plains is a complex phenomenon that is dependent on a variety of factors. The first and foremost is the input of pollutants, followed by weather and local conditions.
• October usually marks the withdrawal of monsoons in Northwest India.
• Once monsoon withdraws, the predominant direction of winds changes to north westerly. During summers, too, the direction of wind is north westerly and storms carrying dust from Rajasthan and sometimes Pakistan and Afghanistan.
• For example, In 2017, a storm that originated in Iraq, Saudi Arabia and Kuwait led to a drastic dip in Delhi’s air quality in a couple of days.
• The dip in temperatures is also behind the increased pollution levels. The inversion height — which is the layer beyond which pollutants cannot disperse into the upper layer of the atmosphereis lowered. The concentration of pollutants in the air increases when this happens.
• Also, high-speed winds are very effective at dispersing pollutants, but winters bring a dip in wind speed over all as compared to in summers.
• Factors such as farm fires and dust storms are added to the already high base pollution levels in the city, air quality dips further.

What are the other big sources of pollution in Delhi?

• Dust and vehicular pollution are the two biggest causes of dipping air quality in Delhi in winters. Dry cold weather means dust is prevalent in the entire region, which does not see many rainy days between October and June.
• Dust pollution contributes to 56% of PM 10 and and the PM2.5 load at 59 t/d, the top contributors being road 38 % of PM 2.5 concentration, the IIT Kanpur study said.