La Nina impacted air quality in India in the winter of 2022

La Nina impacted air quality in India in the winter of 2022

Subject: Geography

Section: Climatology

Context:

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.

More on news:

• The study, by researchers at the Bengaluru-based National Institute of Advanced Studies and Pune-based Indian Institute of Tropical Meteorology, has argued that the unusual air quality in some Indian cities in the winter of 2022 could be attributed to the record-breaking spell of La Nina prevailing at that time.
• Monsoon rainfall over India is known to be strongly influenced by El Nino and La Nina events, the alternating warming and cooling of the eastern Pacific Ocean that impacts weather across the world.
• A new study by Indian researchers has now suggested that even air quality in the country could be influenced by the two weather events.
• 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.
• A rare triple dip La Nina episode, said to be a mark of climate change, set off a peculiar air quality trend in the 2022-23 winter season, showed a new study.
• This period was characterized by improved air quality in north India and increased pollution levels in Peninsular India, the report published in the journal Elsevier February 18 stated.
• As per the report, Mumbai became the city to record the highest deterioration with a 30 per cent rise in Particulate Matter (PM) 2.5 levels.
• This was followed by the cities of Coimbatore recording an increase in PM 2.5 levels by 28 per cent and Bengaluru, and Chennai recording a rise in the same by 20 per cent and 12 per cent respectively.
• A newly developed advanced NIAS-SAFAR air quality forecasting model was used. 
• This model is said to combine a chemical-transport model with an indigenously developed modern artificial intelligent algorithm.

What is the link between pollution and winter months in India?

• During October to January, northern Indian cities, particularly Delhi, experience very high concentrations of PM2.5. 
• A variety of meteorological factors such as temperature, moisture, heaviness in air, wind speed and direction, plays a role in trapping pollutants in the lower levels of the atmosphere. 
• These factors are also responsible for transporting pollutants from other regions, particularly those generated by agriculture waste burning in Punjab and Haryana, to Delhi and adjoining areas.
• The western and southern parts of the country have always had relatively lower levels of pollution, because of their proximity to oceans.
• The winter of 2022 showed a significant deviation from this normal. 
• Northern Indian cities, including Delhi, were cleaner than usual, while cities in the west and the south, like Mumbai, Bengaluru and Chennai, experienced worse-than-usual air quality.
• The study said PM2.5 concentrations in Ghaziabad that winter saw a reduction of about 33% from normal, while in Noida, the concentration was 28% below normal. Delhi saw a reduction of about 10%. Simultaneously, the concentrations in Mumbai rose by 30%, while Bengaluru registered a 20% rise.
• It was this anomalous behavior that the researchers had set out to study when they found themselves led to the possible effects of La Nina.

Wind direction

• The most crucial factor in explaining the anomaly of winter 2022 was a change in the normal wind direction.
• During this time, wind usually blows in the northwesterly direction: for example, from Punjab towards Delhi and further into the Gangetic plains.
• This is one of the main reasons why agricultural waste pollutants in Punjab and Haryana flow into Delhi.
• In the winter of 2022, however, the wind circulation was in the north-south direction. 
• The pollutants being carried from Punjab and Haryana bypassed Delhi and surrounding areas and flew over Rajasthan and Gujarat to southern regions.
• “There was no change in the local sources of emissions in Delhi and Mumbai. But the additional pollutant load from the northern states, which usually lands in Delhi and surrounding areas, moved in a different trajectory and reached peninsular India, some landing in Mumbai as well,” explained Gufran Beig, the lead researcher and one of the leading air pollution experts in the country.
• The local circulation of wind near Mumbai also had an anomalous behavior that year. 
• Wind currents alternate between blowing from the land to the sea every few days. 
• When blowing from the land towards the sea, the winds carry pollutants out of the city.
• In 2022, however, instead of changing direction every four to five days, the winds persisted in one direction for more than a week or 10 days, leading to greater accumulation of pollutants in Mumbai.

La Nina and climate change:

• La Nina events might produce noticeable changes in wind circulation over India.
• This one was a particularly strong event.
• And the impact on air circulation became evident only in the third year of La Nina. So, there may be an accumulative effect.
• It was not yet entirely clear whether El Nino would produce an opposite effect for air quality over India.
• The study did add that changes in wind patterns were not the only reasons for the unusual trends in air quality that year.
• It mentioned local meteorological conditions, unrelated to La Nina, that could also have resulted in the reduction of pollutant concentrations over northern India.

Triple Dip LaLina:

• The 2022-23 winters did coincide with the last phase of a rare triple-dip La Nina event, the first in the 21st century.
• This phenomenon, which was an influence of climate change, had impacted  the large-scale wind pattern playing a decisive role in prevention of stagnation conditions in cities of North India, thus improving air quality.
• In North India, Ghaziabad recorded the most significant improvement with a reduction of 33 per cent, which was closely followed by Rohtak and Noida with a reduction of 30 per cent and 28 per cent, respectively.
• Landlocked Delhi in the northern plains of India, notorious for its unhealthy air, also recorded an improvement with a reduction of about 10 per cent in the winter months of 2022-23.
• In contrast, the atmospheric pattern led to calmer conditions in peninsular Indian cities, accelerating transboundary pollution and significantly deteriorating air quality.
• To understand the association of La Nina-induced changes in large-scale wind pattern and variability in particulate pollutants in 2022 across various regions in the country, the study authors utilized the chemical transport model as a primary methodology. They also carried out sensitivity simulations to validate their findings.
• While extreme weather and changing climate patterns take a heavier toll on the planet, new trends in the frequency of severe pollution events are taking a toll on a regional scale, hence threatening health and food security, the study concluded.

About La Nina:

• It means the large-scale cooling of ocean surface temperatures in the central and eastern equatorial Pacific Ocean, together with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall.
• It has the opposite impacts on weather and climate as El Nino, which is the warm phase of the El Nino Southern Oscillation (ENSO).

Weather Changes due to La Nina:

• The Horn of Africa and central Asia will see below average rainfall due to La Nina.
• East Africa is forecast to see drier-than-usual conditions, which together with the existing impacts of the desert locust invasion, may add to regional food insecurity.
• It could also lead to increased rainfall in southern Africa.
• It could also affect the South West Indian Ocean Tropical Cyclone season, reducing the intensity.
• Southeast Asia, some Pacific Islands and the northern region of South America are expected to receive above-average rainfall.
• In India, La Niña means the country will receive more rainfall than normal, leading to floods.