Delhi Air Pollution: Is Government’s Satellite Monitoring Missing Stubble Fires?
Air Pollution 06/11/2024 •
Smog envelops a South Delhi building – two images from the same spot but a month apart. 

For some years, the Indian government has monitored farm fires, a major source of Delhi’s air pollutions. Officials say the fire count is drastically down as a result, but researchers say their satellite surveillance is missing fires.

DELHI – Peak pollution season has been building up for the last few weeks, and a major government hospital says that cases are rising at its pollution clinic.

On 1 November, the city was the world’s most polluted city thanks largely to Diwali celebration firecrackers the day before – despite a firecracker ban passed in 2018. 

But the worst ranking came a couple of days later when there were few firecrackers but farm fires in two states, Punjab and Haryana, north-west of the Indian capital. 

At a hearing on air pollution a week before Diwali, the Supreme Court criticised both state governments and the government of India for failing to act against polluters, thus making the Environment Protection Act “toothless”. 

Advocate Aparajita Singh, acting as amicus curiae at the hearing, pointed out that neither the 2018 ban on fireworks nor regulations on stubble burning were being implemented. 

“Farm fires and stubble fires are a deadly combination,” Singh told the hearing.

Underscoring that citizens have the right to live in a pollution-free environment according to Article 21 of the Indian Constitution, the court directed the governments to initiate penal action against those setting fires.

These are usually farmers trying to clear the paddy stubble in time to sow the next crop. The court pointed out that despite some 1,000 fires in Punjab reported by the time of the hearing, fewer than 500 people had been fined. 

By 23 October, when the court directed the government to take action, it was reported that the pollution was so bad that the Chief Justice of India, D Y Chandrachud told reporters that he had stopped his early morning walks.

However, the states and central government all asserted at the hearing that they are taking measures that are having an effect.

The crux of their three-fold defence at the hearing is, first, that they are providing funds and subsidised machinery to help farmers clear the paddy stubble without burning,  second, that they are penalising farmers and charging them and third, as a result, the number of fires has reduced over the years.

A few days after the court directive, India’s agriculture minister Shivraj Singh Chouhan, said that the number of fires has halved in the last seven years, and by 35% in Punjab and 21% in Haryana, which impacts Delhi’s air quality. 

Scientists question drastic decline in farm fires 

But researchers told Health Policy Watch (HPW) that they doubted that there had been a decline in the fire count has happened. They base this on satellite observations of fires, burnt areas, and pollutants (aerosols) as well as ground measurements. 

The official fire count in Punjab has fallen from almost 79,000 in 2021 to roughly 32,000 in 2023, whereas in Haryana it’s gone from about 11,000 to about 3,300. 

These numbers are based on images from two satellites that pass over the region at around 10:30am and 1:30pm daily.  But researchers say that these satellites miss many fires as they are usually started later in the afternoon. 

Dr Hiren Jethva, a senior research scientist at NASA Goddard Space Flight Center and affiliated with Morgan State University., tweeted that while the downward fire trend has been drastic in 2022, 2023, and 2024, the aerosol loading, or pollutants, in the atmosphere has increased or remained near stable compared to previous years. 

This, he says, “raises suspicion” that farm fires are ignited after the satellite overpass time, which means the satellite cannot ‘see’, and therefore, detect the active fires.

“The total aerosol loading over the Indo-Gangetic Plain, in which carbonaceous smoke aerosols emitted from the farm fires are a major component around this time of the year, retrieved from the space doesn’t corroborate such decline,” Jethva told HPW.

“This raises a serious doubt that farm fires may not have gone done in previous years,” said Jethva. “Since the timing of igniting farm fires has been shifted to late afternoon, the fire counts show a downward trend.”

Jethva corroborates this assertion with another source: a South Korean satellite GEO-KOMSAT 2A. He points to two images from this satellite taken on 1 November 2024 (see below). The first is taken at 1:30 pm (India time) when the satellite on which the fire counts are based, makes an overpass. The second is taken at 4:20 pm. Unlike the polar-orbiting satellite making once or twice a day overpass, the geostationary satellite continuously monitors the same region at high frequency.

 The second image shows fires just a few hours later.

Pic Left: few or no fires at 1:30 pm IST on 1 Nov., and (right) several fires at 4:20 pm.

Jethva also investigated the shortwave-infrared signal, which is sensitive and useful to detect active fires, from the same satellite, and found a statewide eruption of fires in Punjab during later afternoon hours. 

 Dr Piyush Bharadwaj, an air quality scientist at Bengaluru-based Center for Study of Science, Technology and Policy (CSTEP), told HPW, that “many farmers in Punjab set the fires overnight which generally are not detected” in the morning and afternoon satellite overpass. 

Bharadwaj says another reason for the lower fire count could be that the overpass satellite uses instrumentation (MODIS) with a 1 sq km pixel resolution. 

“Many of the farm fires are much smaller than this,” says Bharadwaj who is Group Head of Atmospheric Composition Modeling group at CSTEP.

His group’s analysis of the fires during the last three years has shown a reduction of daytime fires from ~2500 to ~1000 fire counts, which is a 60% reduction. Even if there has been a decline in fire counts, as claimed by the government, this does not seem to have led to a decline in pollution over Delhi, Bharadwaj adds. 

“Delhi air quality on a year-to-year basis is determined by changing burning activity, meteorology and other emission sources. To our knowledge, the air quality has not improved over Delhi, and/or hard to say with the last five years of data.” 

A recent report by Dr Palak Balyan, of Climate Trends in Delhi, echoes this. Tracking the data in the stubble burning months of September to December from 2019 to 2023, Balyan found that while the fire count dipped by about 23% in Punjab and 44% in Haryana, the air quality index (AQI) in Delhi dipped only by about 5%. 

Fires fall 23 and 44% but Delhi’s AQI dipped only 5%

State 2019 2023 %change (’19-’23)
Punjab fire count 68550 52722 -23.09
Haryana fire count 14122 7959 -43.64
Delhi’s AQI 214.62 203.63 -5.12

Source: Climate Trends

Balyan further explains how much Punjab and Haryana’s fires impact air pollution in Delhi during September and December. Without the fires, the AQI in Delhi averages about 175, which is ‘moderate’ air quality as per the Indian air quality standards.

When the fire count goes up to about 600, the AQI worsens to 233 which is ‘poor.’ Beyond a fire count of 600, the AQI deteriorates to approximately 337 which is ‘very poor,’ when the official health warning reads respiratory illness on prolonged exposure. 

Fire activity AQI Category % Days
No Fire (Fire counts =0) 175 Moderate 5%
Climatological Fire activity

(Fire counts=500-600)

 233 Poor 2%
Above Climatological Fire

(Fire counts> 600)

 337 Very Poor 21%
Below Climatological Fire (0<Fire counts< 500) 229 Poor 72%

Source: Climate Trends

“Our analysis reveals a notable impact of fire incidents in Punjab and Haryana on air quality in Delhi,” says Balyan. “Specifically, it was found that fire incidents (September to December, 2019 to 2023) in these neighbouring states contribute to an increase in Delhi’s Air Quality Index (AQI) by approximately 103 units.”

A recent study submitted to the Delhi state pollution control committee shows just how much burning biomass contributes to Delhi’s pollution in November and December, which tend to be peak pollution months. 

Biomass burning, of which stubble fires are only one component, contributes 36% to air pollution in November but this dips to 21% in December. November is the time when farm fires peak and are largely stopped in Punjab and Haryana.

Biomass burning: November and December.

Researchers say there needs to be a ground-truthing exercise to accurately gauge the totality of farm fires. Additionally, a geostationary satellite with high-resolution and very frequent imagery over north India is needed.

HPW reached out to a spokesperson for the ruling party in Punjab but there has been no response for over three days till filing this report. 

Image Credits: Hiren Jethva.

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