Drop in temperature, change in wind direction and stubble burning usher back smog in Delhi
Air quality over the national capital will worsen and will be in the ‘Very Poor’ category over the next five days, according to the Union Ministry of Earth Sciences.
The air quality is considered to be ‘Very Poor’ when the Air Quality Index (AQI) is from 301-400, according to the Central Pollution Control Board guidelines.
An AQI of 0-50 is considered ‘good’, 51-100 ‘satisfactory’, 101-200 ‘moderate’, 201-300 ‘poor’ and 401-500 ‘severe’. Above 500 is the ‘severe-plus or emergency’ category.
Stubble fires over Punjab, Haryana and Uttar Pradesh, which have started recently, were responsible for approximately 10-25 per cent of Particulate Matter (PM2.5) concentration October 29, 2021, according to the ministry.
“Crop residue burning fire points were observed in Punjab (761), Haryana (134) and UP (21) onOctober 28. The contribution of biomass burning in PM2.5 concentration is likely to be approximately 10-25 per cent October 29,” the Air Quality Early Warning System for Delhi that comes under the ministry, said in a release.
However, the primary factors responsible for the worsening of air quality are a drop in temperature and changes in wind direction over the capital, according to experts at Delhi-based non-profit Centre for Science and Environment (CSE).
A look at the ministry’s forecast confirms this. It noted:
Predicted maximum mixing depth is likely to remain 1,400 metres on 29.10.2021, 1,450 metres on 30.10.2021 and 2,150 m on 31.10.2021 over Delhi. Ventilation index is likely to be 2,500 square metres on 29.10.2021, 12,500 sq m on 30.10.2021 and 31.10.2021. A ventilation index lower than 6,000 sq m with average wind speed less than 10 kilometres per hour is unfavourable for dispersion of pollutants.
On October 30, the predominant surface wind is likely to come from the northwest of Delhi, with a wind speed of 08-14 kmph.
On October 31, the predominant surface wind is likely to come from the west / northwest of Delhi, with a wind speed of 08-12 kmph.
“Considering rising levels of PM2.5 coupled with meteorological conditions that are unfavourable for dispersion, the authorities must implement strict measures related to local air pollution control from all sources,” Vivek Chattopadhyaya, senior program manager, Clean Air and Sustainable Mobility, CSE, said.
He added that regional air quality management should also be strengthened with more legislative backing and enforcement.
“Implementation on ground will require day-to-day monitoring,” he noted.
The priority areas should be curtailing crop residue burning as much as possible, strong action on polluting industrial units, stopping garbage burning, vehicular pollution control measures, among others.
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Smog over Delhi on the morning of October 28, 2021. Photo: @shivamudgil / Twitter
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