Context: 

The recent study Published in the Elsevier Journal emphasised that besides local emissions, rapidly changing climate is a significant factor affecting air quality in India.

La Nina Impacted Air quality in India in the Winter of 2022: Study

• The study was conducted by the  National Institute of Advanced Studies, Bangalore and the Indian Institute of Tropical Meteorology, Pune.
• La Nina Influence on Air Quality: The Study has argued that the unusual air quality in some Indian cities in the winter of 2022 could be attributed to the La-Nina prevailing at that time.
• First Time Connection: This is the first time that air quality in Indian cities has been linked to a La Nina event — and indirectly to climate change, which is making El Nino and La-Nina more severe.

Key Finding of the Study

• Anomaly In Usual Condition (2022): West Indian and south Indian cities like Mumbai, Bengaluru and Chennai, experienced worse-than-usual air quality while Northern Indian cities, including Delhi, were cleaner than usual.
  • For Example: PM2.5 concentrations in Ghaziabad in 2022 winter saw a reduction of about 33% from normal levels while Delhi saw a reduction of about 10% whereas Mumbai saw a rise in PM2.5 by  30%, and  Bengaluru registered a 20% rise.
• Triple dip La Nina: The researchers used the global air circulation data as a result of La-Nina and equated it with the wind patterns over the Indian region. 
  • These anomalous wind patterns showed a strong sensitivity to the prevailing  La Nina conditions and disappeared when these conditions were not present.

How Has La Nina Affected Air Quality?

• Change in Wind Direction: The normal wind direction ie, a North-westerly direction during winters changed to a North-South direction.
  • As a result the pollutants and smoke from stubble burning being carried from Punjab and Haryana bypassed Delhi and Gangetic Plains  and flew over Rajasthan and Gujarat to southern regions.
• Deviation in local wind circulation near Mumbai: In 2022, the local winds persisted in one direction for more than a week or 10 days instead of changing direction every four to five days. 
  • Wind currents alternate between blowing from the land to the sea every few days.
  • It led to a greater accumulation of pollutants in Mumbai as the winds carried pollutants out of the city when they blew from the land towards the sea. 

News Source: Indian Express