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Context: The study conducted by researchers at the National Institute of Advanced Studies and the Indian Institute of Tropical Meteorology sheds light on the link between La Nina events and air quality in Indian cities, particularly during the winter of 2022.

Details

• El Nino and La Nina events are known for influencing monsoon rainfall over India, with the alternating warming and cooling of the eastern Pacific Ocean affecting global weather patterns.

Link between Pollution and Winter Months in India

• During October to January, northern Indian cities, especially Delhi, typically experience high concentrations of PM2.5.
• Meteorological factors such as temperature, moisture, air heaviness, wind speed, and direction play a role in trapping pollutants in the lower atmosphere.
• Pollution transport is influenced by winds, often carrying pollutants from regions like Punjab and Haryana due to agricultural waste burning.

Deviation in Winter 2022

• The winter of 2022 exhibited a significant deviation from the norm, with northern cities being cleaner than usual, while western and southern cities, including Mumbai, Bengaluru, and Chennai, faced worse-than-usual air quality.
• 5 concentrations in Ghaziabad saw a 33% reduction from normal, while Delhi experienced a 10% reduction. In contrast, Mumbai witnessed a 30% increase, and Bengaluru registered a 20% rise in PM2.5 levels.

Impact of La Nina on Air Quality

• Changes in wind patterns were identified as a crucial factor in the anomaly of winter 2022.
• Normally, winds blew in a northwesterly direction from Punjab towards Delhi, carrying pollutants. However, in 2022, wind circulation was north-south, causing pollutants to bypass Delhi and flow over Rajasthan and Gujarat towards southern regions, including Mumbai.
• Anomalous wind behavior near Mumbai also contributed to pollutant accumulation, with winds persisting in one direction for an extended period.

Extended La Nina and Climate Change

• The extended La Nina conditions over the three years influenced wind patterns, and when global air circulation data from La Nina was used in computer models, it showed similar patterns to those observed in 2022.
• The sensitivity to La Nina conditions was evident when comparing models with and without strong La Nina events.

Accumulative Effect and Uncertainty with El Nino

• The impact on air circulation became evident only in the third year of La Nina, suggesting a potential accumulative effect.
• It remains unclear whether El Nino, the counterpart to La Nina, would produce an opposite effect on air quality over India.

El Niño v/s La Niña

Aspect	El Niño	La Niña
Ocean Temperature	Warmer-than-average sea surface temperatures in the central and eastern Pacific Ocean.	Colder-than-average sea surface temperatures in the central and eastern Pacific Ocean.
Atmospheric Effects	Weaker trade winds, leading to changes in atmospheric circulation patterns.	Stronger trade winds, influencing atmospheric circulation patterns.
Rainfall Patterns	Enhanced rainfall in the central and eastern Pacific, leading to flooding in some regions.	Reduced rainfall in the central and eastern Pacific, often causing drought in some areas.
Upwelling	Reduced: Less upwelling of cool water due to weaker winds.	Increased: Increased upwelling of cool water due to stronger winds.
Global Effects	Increased rainfall: California, South America, East Africa Drought: Australia, Indonesia, Southeast Asia Warmer winters: North America, Northern Europe Stronger tropical storms: Pacific Ocean	Drought: Southern US, Australia, East Africa Increased rainfall: Pacific Northwest, Canada, South America Cooler winters: Northern US, Canada Weaker tropical storms: Pacific Ocean
Occurrences	Typically occurs every 2 to 7 years.	Typically occurs every 2 to 7 years, but not necessarily in alternating patterns with El Niño.

PRACTICE QUESTION Q. Which of the following is associated with El Niño conditions? A) Cooler than average sea surface temperatures in the eastern Pacific Ocean B) Increased upwelling of cold water from the depths of the Pacific Ocean C) Stronger trade winds blowing from east to west across the Pacific Ocean D) Warmer than average sea surface temperatures in the eastern Pacific Ocean Answer:  D Explanation: El Niño is characterized by warmer than average sea surface temperatures in the eastern Pacific Ocean. (A), (B), and (C) are all associated with La Niña conditions.