Smog circle. ‘Vicious smog circle’ likely unless local emissions are curtailed

Chilly days during the upcoming winter could trap the plains of North India in a vicious smog circle, which means consecutive days of bad air quality would persist, according to SN Tripathi, Head of Department-Civil Engineering, IIT Kanpur, and Steering Committee Member, National Clean Air Programme, Ministry of Environment, Forests, and Climate Change.

The particulate matter (PM) changes its property after coming in contact with fog, paving way for more fog. “Definitely, intense winters would aggravate the situation. It would mean more amount of haze which would lead to increased trapping of pollutants available over the surface. This might lead to formation of smog which would worsen the condition,” he explains.

Vicious smog circle

All these conditions would result in a vicious smog circle, wherein we would not see clearance for days. Also more cold weather is associated with relatively high humidity, which increases the possibility of particulate matter (PM) holding more water.

After fog disappears, water vapour or droplets evaporate leaving the PM behind, Climate Trends, a strategic communications initiative on climate ambition and low carbon development pathways, quotes Tripathi as saying. However, a very tiny chemistry takes place here and thus, the PM is not the same as before. It is more oxidised by that time.

There is a strong relation between oxidised PM and fog condensation nuclei as compared to non-oxidised components. “In fact, smaller droplets oxidise faster and oxidised PM are more efficient and thus formation of fog would be much easier than the previous day,” said Tripathi.

Extra caution called for

Scientists have called for extra caution this season as weather is beyond control and thus focus still remains on curtailing local emissions. “We have to be more cautious this season, as pollution may get worse with chilly winters in the offing. Whatever extra we would see can be compensated only if we reduce the emissions, at least at the regional levels,” says Tripathi.

But if we continue with the same amount of emissions along with unfavourable meteorological conditions, there could be some substantial increase in the pollution levels in the coming season. October had been fairly well in terms of pollution on account of extended monsoon rains and reduced stubble burning. Though pollution might be less, it was still above the permissible limits.

Reduce emissions, or else..

Sagnik Dey, Associate Professor, Centre for Atmospheric Sciences, Indian Institute of Technology-Delhi and Coordinator, Centre of Excellence for Research in Climate Change and Air Pollution, offers a different perspective.

“December and January are the core winter months and we do not expect stubble burning during that time. With record low temperatures likely, we are not left with any other option but to reduce emissions. Otherwise all clubbed together would multiply the impact and pollution would intensify manifolds,” Dey observes.

“We have no control over meteorological conditions, but we can control emissions,” he adds. Delhi-NCR is inching towards some worse air quality days. On and off rains during October had pushed the peak season of stubble burning and the month recorded much fewer farm fire cases than 2020.

Crop residue burning incidents

Data from the ICAR – Indian Agricultural Research Institute shows that total crop residue burning events recorded in the six states this year are 54.8 per cent less than in the same period in 2020. As a result, most of the cities in the six states reported lower concentration of PM 2.5 in September and October 2021 as compared to the last year.

Similarly, average fire counts data in Punjab, Haryana and Uttar Pradesh from NASA for September and October in the past five years show that the average PM 2.5 levels in Delhi were the highest in 2017 when the average fire counts were the highest too.

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