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Monday, November 29, 2021

Delhi air pollution: Farm fire impact peaked on November 7, has been dipping since

Experts say linking Delhi’s poor air to one factor alone would be an oversimplification. After all, the stubble burning season lasts around 45 days, while air in Delhi remains polluted till February.

Written by Mallica Joshi | New Delhi |
Updated: November 16, 2021 8:00:36 am
Delhi pollution, farm fires, stubble burning, delhi AQI, safar, Air Quality and Weather Forecasting and Research, air pollution news, delhi news, Indian Express, India news, current affairs, Indian Express News ServiceA farmer sets paddy stubble on fire at a village Jassar Nera Gill Canal in Ludhiana. (Express Photo: Gurmeet Singh)

As a debate rages on about how much farm fires in Punjab, Haryana and Uttar Pradesh affect the air quality in the national capital, the System of Air Quality and Weather Forecasting and Research (SAFAR), which comes under the Central Ministry of Earth Sciences, has been keeping track over the years.

According to them, the share of stubble burning in the PM 2.5 concentration in Delhi’s heavily polluted air touched a peak of 48% on November 7, when the air quality index value clocked in at a severe 428. The primary pollutant was PM 2.5.

SAFAR uses satellite information to calculate the number of fires in the region. These are then fed into a Chemistry Transport Forecast Model, a software that adds this data to existing conditions such as wind direction and speed, temperature, cloud cover, possibility of rain, etc to generate the share of PM 2.5 due to the fires.

While the peak was 48%, it has been dipping since and was 10% on Monday.

According to data available between October 20 and November 15, the contribution has varied from 2% on October 24 to 48% on November 7. Last year, the peak was around 44%.

According to the minutes of the meeting held by the Commission for Air Quality Management (CAQM) Sunday, which was shared with the Supreme Court on Monday, “paddy stubble burning has been contributing about 35%-40% of the total pollution load in Delhi-NCR”.

A 2015 source-apportionment study on Delhi’s air pollution conducted by IIT-Kanpur states that 17-26% of all particulate matter in Delhi in winters is because of biomass burning.

But experts say linking Delhi’s poor air to one factor alone would be an oversimplification. After all, the stubble burning season lasts around 45 days, while air in Delhi remains polluted till February.

According to experts, the city’s air quality is affected by a myriad of factors, and the impact of local sources — vehicles and industries — cannot be overstated.

“Farm fires will stop in a few days; they have already started decreasing. What Delhi needs is a long-term plan to tackle its own sources as well. This is not to say that farm fires are not a problem or a contributing factor. They are, but in the short term,” said a Delhi government official.

Professor S N Tripathi from IIT-Kanpur, which did the first source apportionment for the Delhi government in 2015, said vehicular emissions and pollutants from industry are proving to be the main sources of pollution in the city through the year.

“The percentage contribution of stubble burning will be around 25%-35% at its peak. We can see already it has started to decrease. We have now realised that even road dust is not a very big contributor. The contribution of traffic goes beyond 20%. This is when we look only at vehicles as primary sources of pollution. Vehicles also emit gasses which can turn into particulate matter over time as secondary particles. If that is considered, the contribution increases to around 25%,” he said.

When contribution from industries is accounted for, which are also responsible for primary and secondary particles, it is clear that traditional sources of pollution remain the same as in 2015, he said. “Urgent action is needed to address pollution from BS IV compliant vehicles. While we have moved to BS VI, many vehicles are still only BS IV compliant. Some form of retrofitting should be done to address this,” he said.

Delhi’s air quality dipped on Monday as compared to Sunday. While both days were in the ‘very poor’ category, the AQI value on Monday was 353 as compared to 330 on Sunday.The air quality is expected to be in the very poor range for at least three more days.

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