AQI ‘severe’ again as farm fires hit record
The AQI on Tuesday, according to the 4pm health bulletin, was 404, worse than the 390 on Monday.
Delhi’s air quality index (AQI) slipped back into the “severe” category on Tuesday after relenting to “very poor” a day before, coinciding with a spike in farm fires in Punjab and Haryana that has not been seen this late in the month of November since at least 2012.
The AQI on Tuesday, according to the 4pm health bulletin, was 404, worse than the 390 on Monday. The number was above 400 for three consecutive days following Diwali, as emissions from fireworks and smoke from paddy stubble burning combined to create a toxic haze that has persisted since.
At 5,382 and 4,859, instances of fire detected by National Oceanic and Atmospheric Administration’s (NOAA) Suomi-National Polar-orbiting Partnership (Suomi-NPP) mission were at their highest for November 8 and 9 since the satellite began recording this data in 2012.
“We have been demanding a bonus of ₹200 per quintal to enable farmers for disposal of crop residue. Most farmers in Punjab have landholdings of up to three acres and they are not in a position to invest in stubble management. They are left with no alternative than to burn residue,” said senior vice president of the Bharatiya Kisan Union (Ekta Ugrahan), Jhanda Singh Jethuke, while adding that farmers were sensitive to the environmental impact but have been left with little choice.
The average of fire instances recorded between the November 7-9 period was over 5,000 – highest since the 5,481 recorded in 2016, when the Capital faced its worst spell of toxic smog.
A high number of farm fires in the second week of November is noteworthy since, by this time, farmers should have cleared their fields and begun sowing winter crops. Monsoon has been delayed this year, pushing back summer harvest, and reducing the window that farmers have to clear the fields for the next cycle.
Another possible reason for the delay in harvest could be that the central government had postponed paddy procurement from October 1 to 11.
The improvement in AQI seen on Monday was merely numerical, with conditions outside as hazy as they have been since the day of Diwali. Wind speeds picked up to 8-10 km/hr on Monday during the afternoon but began to drop by late evening and had become “calm” in the early hours of Tuesday.
This pattern is likely to be repeated for the next 4-5 days, which will mean the air quality will range between “very poor” and “severe”, a subcommittee of the Commission on Air Quality Management (CAQM) in NCR warned.
According to System of Air Quality and Weather Forecasting And Research (Safar), the share of farm fires in Delhi’s air was 27%, down three percentage points from Monday’s 30%.
Safar’s estimation of farm fires based on satellite data varies marginally to the Fire Information for Resource Management System (FIRMS) data accessed by HT.
Delhi recorded the season’s lowest minimum temperature of 13.5°C on Tuesday, and IMD forecasts show the minimum could drop to 10 degrees by November 15 as cold northwesterly winds continue to blow. This means a pollution double whammy for the Capital -- not only does particulate matter settle near the ground when the temperature falls, northwesterly winds carry smoke from stubble fires towards the city from Punjab and Haryana while the more favourable easterly winds carry it away.
Hourly PM 2.5 data from the Delhi Pollution Control Committee (DPCC) shows peak pollution levels occurring between 3am and 5am at most stations in Delhi, crossing 500 micrograms per cubic metre in concentration – eight to nine times the national safe limit of 60 micrograms per cubic metre.
Dr Pratima Singh, who leads the Air Pollution Studies at the Center for Study of Science, Technology & Policy (CSTEP), said as the temperature starts to drop at night, the air becomes cold, and restricts movement of pollutants. “The mixing layer comes down and traps pollutants closer to the surface and relief is only seen when the sun is out and temperatures increase, allowing this mixing layer to lift up,” said Singh, stating a peak in pollution levels can occur around 6-7 am, with a second peak generally observed after 9am, when emissions from vehicles are usually at their highest.
“There is more accumulation of pollutants taking place than there is dispersal and this is building up, particularly in the early morning hours and late at night,” said Dipankar Saha, formed head of CPCB’s air laboratory.
The Council on Energy, Environment and Water (CEEW), in their own analysis of the spike in pollution, said on November 8 the wind speed was 13 km/hr at 5pm as PM 2.5 concentration dropped to 154 micrograms per cubic metre. However, when wind speeds dropped by 5am the next day, Delhi’s PM 2.5 concentration was at its peak of 352 micrograms per cubic meter.
“Meteorological parameters like wind speed and direction significantly influence air quality. While faster surface winds as observed post-noon favour dispersion of pollution, lower wind speeds typically observed early in the morning prevent dispersion of pollution. This results in higher concentration of PM2.5 and PM10 in the early morning hours and declining values as we approach noon,” said Tanushree Ganguly, programme lead at CEEW.
Dr JC Suri, senior pulmonologist and director, respiratory diseases at Fortis Hospital in Vasant Kunj, said pollution levels beyond “satisfactory” begin impacting high-risk groups such as children and those suffering from respiratory diseases; however, air between “very poor” and “severe” impacts all age-groups and puts even healthy people at risk. “High-risk people should particularly not venture out in such air quality and if one needs to, wearing a mask is a must. One can check out air quality and head out when pollution levels are at their lowest, with morning and evening time generally considered the worst,” he said.
Suri also warns that, in the short term, exposure to such air can lead to irritation in the eyes and throat and if levels are particularly high, can even precipitate acute heart attacks. “In the long run, one can develop cancer, diabetes and polluted air also impacts brain development,” he warned.