Bengal Braces for Intensified Winter Air Pollution Partly Thanks to Delhi

This rise in air pollution in Bengal is due to a mix of both natural and man-made factors working simultaneously.

(Photo: Debayan Dutta / The Quint)

Shortly after Diwali, Delhi saw severe AQI levels and smog across the region because of stubble burning in the adjacent states of Punjab and Haryana, as well as the pollution caused during Diwali.

While the pollution levels seem to be subsiding in Delhi, Bengal is set to feel the brunt of the same pollution, as winter sets in.

This rise in air pollution in Bengal can be attributed to a mix of both natural and man-made factors, which have been working in tandem.

Anthropogenic or man-made activities have already pushed the air quality beyond safe levels, making Delhi and Kolkata the worst and the fourth worst polluted city in the world. But when natural phenomena play a part, then the result is worse.

Kolkata had seen similar conditions back in 2018, when for a fortnight (November to December 2018), its air quality was worse than Delhi.

But to understand why Kolkata stands at the crossfire of this intense winter air pollution, one needs to first understand the topography of the region and the Indo-Gangetic plains (IGP).

How Pollutants Travel From Delhi to Bengal

West Bengal is situated at the eastern side end of the Indo-Gangetic plains which include Delhi, Haryana, Uttar Pradesh and Punjab. Usually, the air pollutants that originate from the northwestern plains (Delhi, Haryana, UP and Punjab) travel down the plains, passing through West Bengal and finally dispersing over the Bay of Bengal.

According to Dr. V Vinoj, Assistant Professor at The School of Earth Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar - the pollutants are in fact directed towards this route because of the presence of mountains both to the north and the south of the Gangetic plains.

Therefore, during winters, Eastern Indian regions including West Bengal have higher levels of transported air pollution, further enhanced by high levels of local anthropogenic emissions.

Dr. V Vinoj, Assistant Professor, IIT Bhubaneswar

Now that we have an idea about the topography of Bengal, we can decode the natural phenomena which intensifies the winter air pollution in Bengal.

Metereological Factors Intensifying Pollution

Prof S N Tripathi, Civil Engineering department, IIT Kanpur and Steering Committee Member, National Clean Air Programme, MoEFCC explains that pollution in Bengal intensifies not only because of the pollutants coming in from the Northwestern region but also because of the state’s own local emissions (industrial and vehicular).

Normally, the north-westerly winds would carry all the pollution into the Bay of Bengal and bad air quality over the region might only be temporary. However, any meteorological factors like a pressure belt or calm winds, could result in the pollution staying on like it did in 2018.

S N Tripathi, Professor, IIT Kanpur

This year, these meteorological factors have come in the form of an anti-cyclone and the La Nina current. The anti-cyclone which originated in Jharkhand has been moving eastwards towards Odisha and Gangetic Bengal.

In an anti-cyclonic formation, winds flow in the clockwise direction in the Northern Hemisphere and in the anti-clockwise direction in the Sourthern Hemisphere.

Wherever there is an anticyclone, winds will tend to subside and do not allow mixing. Thus, pollutants will not lift in the atmosphere. As a result, pollutants are transported from north-westerly winds from the northwestern plains along with the local pollutants, would get trapped over the earth surface. Hence, we can expect a sharp spike in pollution levels. The weather system is expected to stay over West Bengal for the next 3-4 days and so will the pollution levels the Southern Hemisphere.

Mahesh Palawat, VP- Meteorology and Climate Change, Skymet Weather.

Due to thick fog and haze, slow winds blow at a low altitude and are also impacted by a localized area of strong subsidence in winter. Thus, the pollutants tend to get trapped at a lower altitude than usual.

The other major factor here is La Nina. North India is expected to experience severe winter this season thanks to La Nina brewing in the Pacific Ocean.

La Nina or ‘Little Girl’ is a weather pattern that forms in the Pacific Ocean where strong winds blow warm water on the ocean’s surface from South America to Indonesia. This results in cold water rising to the surface.

La Nina is forecast to blow over East and North India between December 2021 and Februrary 2022.

The cold wind from La Nina will make the dispersion of particulate matter difficult as this too will prevent the pollutants from rising up in the atmosphere. As the cold air gets trapped under a layer of warm air, it leads to the formation of a thick coat of haze.

Experts have predicted that this will also aggravate pollution levels in the Indo-Gangetic plains. While early winters and intense pollution have already been seen in Delhi and its neighboring states, it won’t be long before West Bengal experiences it too.