After Delhi, the air pollution menace is engulfing West Bengal, too. A recent report by IQAir, a Switzerland-based climate group, had put Delhi, Kolkata and Mumbai among the top 10 most polluted cities of the world.

According to scientists, West Bengal bears the brunt thanks to its being located to the eastern side of Delhi, Uttar Pradesh, Punjab and Haryana in North-West India.

The very nature of topography over Indo-Gangetic Plains covering the region from North-West India down to West Bengal is bounded by mountain ranges both to its North and South. This feature directs most emissions in North India towards east towards the West Bengal, draining eventually into the Bay of Bengal.

An anticyclone over the West Bengal region could intensify the pollution levels in the coming days. The anticyclone is an atmospheric wind flow in upper levels associated with a high-pressure system.

High-pressure system

When such a system forms, the wind starts flowing clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere. This does not allow pollutants to rise and dissipate as in a low-pressure system.

Mahesh Palawat, VP-Meteorology and Climate change, Skymet Weather, says that the anticyclone has shifted bearing to the plains of West Bengal. It forces air to sink and pressure over the ground to rise and does not allow mixing. Thus, pollutants will not lift up in the atmosphere (as in a low-pressure system), says Palawat.

“As a result, pollutants transported from north-westerly winds from the plains of North-West India along with the local emissions get trapped over the surface. Hence, we can expect a sharp spike in the pollution levels. The weather system is expected to stay over West Bengal for the next 3-4 days and so will the pollution levels.”

Pollution spike likely

Similar conditions had developed over Kolkata and adjoining areas of West Bengal back in 2018. As per various news reports, Kolkata’s air quality was worse than Delhi for over a fortnight in November and December 2018.

Particulate matter (PM) 2.5 concentration in Asansol, Howrah, Kolkata and Siliguri has been above the safe limits of 40 ug/m3 (prescribed by the Central Pollution Control Board) during the 2019 winter. Kolkata saw the highest monthly average PM 2.5 concentration of 201 ug/m3 in January 2019.

PM2.5 is monitored at 14 monitors in six cities. Of these, Asansol, Siliguri, Durgapur and Haldia have one continuous ambient air quality monitoring station each. There are three monitors in Howrah and seven in Kolkata.

In urban centres only

The monitors recorded an uptime (the machine and data recorded availability) of 90 per cent as against the requirement of 70 per cent. However, the monitoring continues in urban centres only, says Climate Trends, a strategic communications initiative on climate ambition and low carbon development pathways.

V Vinoj, Assistant Professor, School of Earth Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, says that during winters, East India sees higher levels of transported air pollution, enhanced by high levels of anthropogenic emissions.

Adverse Met features

Normally, pollution over the Bay and bad air quality might only be temporary. But any meteorological factors like a pressure belt or calm winds could help the pollution stay on as it did in 2018, says SN Tripathi, Civil Engineering Department, IIT Kanpur and Steering Committee Member, National Clean Air Programme of the MoEFCC.

North India is expected to witness intense winter this season from evolving La Nina conditions over the Pacific Ocean. With this, unfavourable conditions, as cited above, would aggravate air pollution levels across the Indo-Gangetic plains.