Thermal inversion is a big factor behind the sudden spike in dense smog.
Since Wednesday morning, north India has been covered in a thick blanket of smog, leading to low visibility, a drop in temperature and the air quality deteriorating to the 'Severe' category.
Air quality remained a concern all over the Indo-Gangetic Plains (IGP), with satellite images showing the alarming scale of the smog cover over northwest India including Delhi and its adjoining areas. Punjab, Haryana, Uttar Pradesh, Delhi, parts of north Rajasthan, Himachal Pradesh and Uttarakhand, are covered with smog.
Hiren Jethwa, an aerosol remote sensing scientist at NASA Goddard Space Flight Center, shared the satellite images, detailing the extent of the smog covering the IGP, the reasons behind the dense smog in November, and how the farmers in Punjab are evading NASA satellites by burning crops late afternoon.
Thermal Inversion - A Key Factor
Thermal inversion is a big factor behind the sudden spike in dense smog and pollution levels. Hiren Jethwa, a research scientist at NASA, explained the phenomena and said, "The warmer air sits above the cooler air on the ground and that does not allow the vertical mixing of pollutants and whatever we emit at the surface stays for around 200 metres within the boundary layer. The stronger the thermal inversion, the more pollutants will be trapped near the surface because there is no venting place for the pollutants to go up in the vertical direction."
"In the satellite images, we can notice that smoke from crop burning is mixed with clouds or is above them and that kind of situation furthers thermal inversion because of the absorption of light-absorbing aerosols and that it further warms the upper layer and increases thermal inversion," Mr Jethwa said.
He added that the fog occurrence over the Indo-Gangetic Plain (IGP) has increased and the occurrence has increased in November, which usually took place in December. He explained that there's more particulate matter (PM), which acts as a cloud condensation nuclei which favours the formation of fog and when temperatures go down an enormous amount of aerosols contribute to fog formation.
Farmers Avoiding NASA Satellites?
The CAQM appreciated Punjab for making strenuous efforts to bring down the stubble-burning count by nearly 71 per cent as compared to last year. Mr Jethwa said, "It is not true that farm fires in Punjab and Haryana have gone down." On Monday, farm fires in Punjab alone crossed the 7,000 mark after over 400 fresh cases were registered.
Mr Jethwa claimed that farmers in Punjab are timing crop burning with the overpass of NASA satellites. He said, "We use the afternoon satellite overpass time data from NASA Satellites like Suomi NPP and Aqua. They overpass the region around 1:30-2:00 pm but somehow they (farmers) have learnt that they can bypass the satellite overpass time and can burn the crop residue in the late afternoon. This is confirmed by the South Korean geostationary satellite that the majority of the crop burning happens after 2 pm once the NASA satellites overpass the region when there is no surveillance, but the fires cannot be hidden from geostationary satellites which take a picture of the region every five minutes."
Mr Jethwa in an X post, shared satellite images from October 29, taken by the GEO-KOMSAT A2 satellite, shows a timelapse of the crop-burning activities in northwest India. The images show dense cloud cover over the region post-4 pm, when compared to 1:30 pm, suggesting that farmers are burning crops late afternoon to avoid NASA satellite surveillance.
"The pollution loading in the last two weeks has reached the highest level that we haven't seen in the last 10 years...The crop burning has gone down over a certain period. Still, if we look at the geostationary images, there are many farm fires after 2 pm," he told NDTV today, adding that "the data from geostationary satellite is sensitive to the thermal signal produced by the fire. It lasts for at least four hours."
On whether there has been an increase in burnt area, Mr Jethwa said, "This year, the data is yet to come out, but the fires seen so far until November 14 are 19% of the level seen in 2022 and 35% seen in 2023. Of course, there is a drastic drop around 1:30 p.m., but if we see the burnt area data, there has been no drastic decrease."
Today the data showed that five farm fires were reported in Punjab, 11 in Haryana, and the highest number, 202, in Uttar Pradesh, according to satellite data shared by the Indian Agricultural Research Institute (IARI). As per government data, Punjab recorded 49,922 farm fire events in 2022, 71,304 in 2021, 76,590 in 2020, 55,210 in 2019 and 50,590 in 2018 with many districts including Sangrur, Mansa, Bathinda and Amritsar witnessing a large number of stubble burning incidents.
Mr Jethwa concluded by saying "Yes, farmers can hide the crop burning from the 1:30 pm overpass time but the PM 2.5 data and the pollution load over the Indo-Gangetic plain region, the geostationary satellite data and the burnt...everything is pointing toward fire is still present. Maybe it's still increasing...Smog towers are a small fix. It won't work unless we address the issue of crop burning in the region.
Toxic Air In Delhi
Several factors contribute to pollution in the Delhi-NCR region including the emission of gases from vehicles, stubble burning in Punjab and Haryana and construction and dumping activities.
The situation worsens every year after Diwali due to the bursting of firecrackers, which have been under a blanket ban in Delhi for the last few years.
Last morning, dense smog caused zero visibility at the Indira Gandhi International Airport in Delhi, disrupting flight operations. Meanwhile, the Commission for Air Quality Management (CAQM), the panel tasked with enforcing anti-pollution measures in Delhi-NCR, called it an "episodic event" and expected the situation to improve "owing to stronger winds".
Today, Delhi's Air Quality Index (AQI) was measured at 428 at 9 am, placing it in the 'severe' category. This marks Delhi's worst air quality reading of the season and the highest in the country, with a 24-hour AQI of 418 on Wednesday, an increase from 334 the day prior.
Dr Vivek Nangia, a Pulmonology head at Max Hospital, told NDTV that "Air pollution has been labelled as the single-most hazardous environmental risk factor to our health."
"Large particulate matter of 5 or 10 microns irritates the eyes and sore throat, but the smaller particles go inside the lungs and get absorbed into the bloodstream along with toxic gases, which results in an inflammatory cascade in the body. This is not only restricted to the lungs but the entire body. It could result in brain strokes, heart attacks, panic attacks and various types of cancer, a decreased life expectancy. For the lungs, it could cause illnesses like Asthma and even lung cancer which was earlier labelled as 'smoker's cancer'." Dr Nangia said.
The satellite image shows the whole of Delhi and its adjoining areas covered under a dense layer of smog. The gravity of the situation is better understood when the satellite picture is compared with an image from exactly one year ago. On November 14, 2023, a less dense cloud cover was visible over the Indo-Gangetic plain from Punjab to Uttar Pradesh. On November 14, 2024, the density of the smog cover appears to have doubled than what it was at the same time last year.
The CAQM has today enforced stricter norms to control air pollution, banning all non-essential construction demolition work, and plying of BS III petrol and BS-IV diesel cars, among other actions. The measures will be implemented from 8 am tomorrow.
The Supreme Court today agreed to expedite a hearing on measures to combat the city's hazardous pollution levels on November 18.
Situation In Pakistan
The situation is bad in neighbouring Pakistan too. Most outdoor activities have been banned in the Punjab province of the country, including an early shutdown of shops, markets and malls in some areas to curb pollution-caused illnesses.
Districts of Lahore, Multan, Faisalabad and Gujranwala have reported an increase in patients with respiratory diseases, and eye and throat irritation. "The spread of conjunctivitis/ pink eye disease due to bacterial or viral infection, smoke, dust or chemical exposure is posing a serious and imminent threat to public health," the Punjab government said.
Similar to its cross-border neighbour Amritsar, Lahore is also enveloped in a thick layer of smog, which stretches from west Pakistan, all the way to Saharanpur in western Uttar Pradesh, satellite images show.
Lahore's air quality has remained hazardous for several days with an index score of over 600, according to IQAir. At 8 pm (IST) today, Lahore is the world's most polluted city with an AQI of 1136, as per IQAir. It is expected to drop to 850 by 11 pm (IST). Delhi ranks second on the index with 'very poor' air quality.
For comparison; As per the IQAir monitor, Washington DC is the cleanest city in the world with an AQI of 31.
UNICEF has also called for greater efforts to reduce pollution and protect children's health in Pakistan's Punjab, saying over 11 million children under five years of age are in danger as they breathe the toxic air.
"In addition, schools in smog-affected areas have been closed...the learning of almost 16 million children in Punjab has been disrupted," Reuters reported, quoting, Abdullah Fadil, UNICEF Representative in the country.