Rapid build-up in short timespan able to tip air quality into severe category as local pollution already very high, says thinktank

Photo: Vikas Choudhary / CSE

Delhi’s pollution level — Particulate Matter (PM)2.5 concentration — saw its first huge spike of this winter season on November 2, 2023, with a sudden and staggering 68 per cent jump within 24 hours, according to an analysis by Delhi-based thinktank, Centre for Science and Environment (CSE).

On November 2, PM2.5 levels in Delhi crossed 300 microgram per cubic metre (µg/m3) or ‘severe+’ level for the first time this season, according to the analysis by CSE’s Urban Lab.

PM2.5 levels had started to rise steadily from the beginning of October during the past five years. This year, the levels started to rise from the middle of September, a statement by CSE noted.

Avikal Somvanshi, head, Urban Lab, said:

This kind of rapid build-up is not uncommon during this part of the season and is generally associated with smoke-fall from farm stubble fire and meteorological factors assisting transportation of the smoke to Delhi and the National Capital Region (Delhi-NCR) and topping the high local pollution. But it must be kept in consideration that this rapid build-up in a short time span is able to tip air quality into severe category because baseline pollution from local sources is already very high.

The statement also said pollution from stubble burning on farms in Punjab and Haryana is yet to peak.

“SAFAR’s estimate has shown that the percentage contribution of farm stubble fire to Delhi’s PM2.5 concentration had crossed 25 per cent on November 2; it was in the 10-20 per cent range in the week leading to November 2. This is expected to rise in the coming days,” it said.

SAFAR or System of Air Quality and Weather Forecasting and Research is a country-wide initiative by the Union Ministry of Earth Sciences, with an objective to provide location-specific information about air quality on a real-time basis.

CSE added that the fire instances in Punjab and Haryana are yet to peak. In previous years, the contribution from farm fires on the worst days of Delhi-NCR’s smog had topped 40 per cent, as generally noted during the middle of November.

The analysis noted that most of the pollution this time was due to combustion. It said:

The share of PM2.5 in PM10 is an important indicator of the impact of combustion sources. While coarser PM10 comes largely from dust sources, the tinier PM2.5 come more from vehicles, industry and open burning. This year the percentage share of PM2.5 in PM10 has crossed 50 per cent, which indicates higher impact of combustion sources. On November 2, the ratio for PM2.5 stood at 60 per cent — highest this season indicating the higher influence of combustion sources. 

NO2 or Nitrogen Dioxide levels are also rising in the region. NO2 largely comes from vehicles. The average NO2 level across Delhi is up by 60 per cent compared to the first week of October last year. Certain high traffic locations have been reporting levels as high as three-four times the 24-hour standard, according to CSE.

About 13 pollution hotspots that were identified in 2018-10 continue to remain a challenge, while newer hotspots are emerging as well.

Mundka and New Moti Bagh are the most polluted locations in Delhi, with average PM2.5 levels exceeding 300 µg/m3. The worst polluted new hotspots in Delhi are New Moti Bagh, Nehru Nagar, Sonia Vihar and DU North Campus. Greater Noida, Noida Sector 62, Loni and Faridabad are the most polluted locations in NCR.

ITO is most polluted NO2 location in Delhi, with an average of 219 µg/m3. Nehru Nagar and Siri Fort are the next most polluted NO2 locations in Delhi.

“While several measures have been taken over the years to clean up fuels and technology across transport and industry sectors, and control dust sources, more action is needed at a scale and speed to address the remaining policy gaps for meeting the clean air targets. Only this can prevent building up of such smog episodes endangering public health,” Anumita Roychowdhury, executive director, research and advocacy, CSE, said.

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