How Delhi became gas chamber twice this year

NEW DELHI: Two high-pollution events, with smoggy weather and “emergency” level air quality readings, were recorded in November 1-5 and 11-15. The causes of these episodes, according to experts, were largely meteorological factors. Understanding weather behaviour is key to planning anti-pollution measures, they said.
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“The major reason for the build-up of pollutants was the absence of wind,” said an official of the Indian Meteorological Department.“Unlike in 2018, there were no active western disturbances this year to clear the region of pollution.”

Two earlier years had seen smog episodes during October 28-November 6 in 2016 and November 7-14 in 2017. However, last year, active western disturbances on November 2-4 and 14-16 helped the city avoid the haze.
The IMD official said, the western disturbances this year didn’t result in much rain over Delhi-NCR. “The pollutants remained undispersed, in fact got aggravated due to moisture and low temperature,” he said. “Though low wind is predicted for next week, there are fewer crop fires now, so the air quality might not reach such toxic levels again.”
Just after Diwali, the November 1-5 period saw pollution created by burning of paddy harvest residue in neighbouring states and blown to Delhi accounting for 44% of the capital’s PM2.5 pollutants. A slight drizzle on November 2 worsened the situation, making November 3 the foulest day in Delhi this season.
“Rain washes away pollutants, but light drizzles and calm wind conditions adversely affect air quality,” the expert said. “Secondary particles, such as sulphates, nitrates, ozone and organic aerosols, are products of complicated atmospheric reactions between primary particles, such as particulate matter, sulphur dioxide and nitrogen dioxide directly emitted by stubble burning and vehicles in the presence of factors like sunlight and moisture.”
In the second episode from November 11-15, cloud cover and a slow wind speed due to a western disturbance did not allow dispersion of the accumulated pollutants.
Dipankar Saha, former head of Central Pollution Control Board’s air laboratory, noted that the intrusion of trans-boundary dust was also on the rise. “We getting less rainfall in June and July and more in September and October,” he said. “This is causing late harvesting and so forcing farmers to resort to harvest residue burning. We need to have a clear-cut understanding of meteorological behaviour and plan accordingly.”
Saha said that the analyses of these high-pollution episodes showed that their frequencies were increasing over the years. “Concentrations of the fine PM2.5 pollutants are also rising,” he added. “The root cause is lack of land-use planning and locally originated emissions.”
According to Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment, sustained anti-pollution action is the need of the hour for cleaner air in the region. “Winter is vulnerable to high smog episodes. Adverse weather conditions, high local pollution and transport of pollutants are big factors,” she said. “But we should leverage this crisis for a sustained action to eliminate dirty industrial fuels, upscale public transport and push for zero-waste solutions across Delhi-NCR to bring a reduction in round-the-year pollution.”