Bengaluru: On November 18, Delhi was once again suffocated by “Severe” air quality. As per the Central Pollution Control’s Board (CPCB’s) daily Air Quality Index (AQI) bulletin, Delhi’s AQI was 494 as of 4 pm on the day, with the prominent pollutant being fine particulate matter.
Starting Monday (November 18), the Delhi government has now implemented Stage IV of the Graded Response Action Plan (GRAP) which bans most construction activity in the NCR, along with other actions such as banning the entry of trucks into Delhi (except for those carrying essential commodities or those providing essential services).
The Supreme Court ordered that physical classes for all school students up to Grade 12 in Delhi be suspended for the time being due to the pollution. It also came down heavily on the Commission for Air Quality Management for not implementing Stages III and IV of GRAP earlier, LiveLaw reported.
This “hazardous situation” of air quality has emerged due to our inability to curb pollution from perennial sources, which are both local and regional, including emissions from industries and power plants, an air quality scientist told The Wire.
Screengrab from CPCB website.
Delhi AQI shoots up to 494
As per the CPCB’s daily AQI bulletin on November 18, the prominent pollutant was PM2.5. The bulletin is based on data from 36 out of the 39 monitoring stations in the city.
On November 17, the AQI was in the “Severe” category as well, at 441.
India’s AQI is a measure of levels of at least three pollutants. One of them is particulate matter (both PM2.5, which is fine particulate matter of diametre less than 2.5 microns, and PM10, which is less than 10 microns in diametre). The AQI ranges from 0 to 500, and the higher the AQI, the higher impacts of such air on even healthy people. While an AQI between 0 to 50 is considered ideal, an AQI between 401-500 is categorised as “Severe”, and is the worst air quality level per standards followed by the CPCB. Exposure to such air quality, “affects healthy people and seriously impacts those with existing diseases” as per the CPCB. Per India’s National Ambient Air Quality Standards (NAAQS) of 2019, such air quality “may cause respiratory effects even on healthy people and serious health impacts on people with lung/heart diseases. The health impacts may be experienced even during light physical activity.”
This “Severe” air quality is what the people of Delhi are currently living through.
Screengrab from CPCB website.
Per the November 18 bulletin published on the Air Quality Early Warning System for Delhi, which is managed by the Indian Institute of Tropical Meteorology, Pune, “meteorological conditions are likely to remain extremely unfavourable for effective dispersion of pollutants”. Per the bulletin, the air quality is likely to remain in the “Severe” category from November 19 to 21. Over the subsequent six days, it is likely to be either in the “Severe” or “Very Poor” category.
There are also reports of desperate attempts to decrease the readings in automatic weather monitoring stations. One source spoke of officials at monitoring stations deploying large fans and sprinkling water to reduce levels of particulate matter being captured in the automatic monitoring systems.
The levels of particulate matter in Delhi are now way above even the CPCB’s lax standards.
As per India’s National Ambient Air Quality Standards (NAAQS) of 2019, the concentration of particulate matter PM10 (particulate matter that is less than 10 microns in diameter) in ambient air is 100 µg/m3 (micrograms per cubic meter) across a 24-hour period, and 60 µg/m3 annually. For fine particulate matter or PM2.5 (particulate matter that is less than 2.5 microns in diameter), it is 60 µg/m3 for a 24-hour period, and 40 µg/m3 annually.
The World Health Organisation (WHO), however, has more stringent standards. It recommends that levels of PM2.5 should be no more than 15 µg/m3 for a 24-hour period (and 5 µg/m3 annually). Similarly, PM10 levels should not be more than 50 µg/m3 for a 24-hour period (and 20 µg/m3 annually). Per the WHO, which decreased these limits in its latest guidelines in 2021, even low concentrations of these pollutants cause significant health risks.
Screengrab from CPCB website.
The Delhi government implemented Stage III of the Graded Response Action Plan (GRAP) on November 14. On November 18, it implemented Stage IV of the GRAP. These rules ban most construction activity in the NCR, along with other actions such as banning the entry of trucks into Delhi (except for those carrying essential commodities or those providing essential services).
Unfavourable meteorology
“It was very well known that around this time of the year the wind speed decreases, temperatures drop and the predominant wind direction becomes north-north westerly, coming in from the Haryana-Punjab side,” Sunil Dahiya, founder at Envirocatalysts, an organisation that works on achieving clean air, told The Wire. “These unfavourable meteorological conditions help in the build up and stagnation of pollution creating an inversion layer (which prevents the pollutants from dispersing in the atmosphere) and thus increases the concentration of pollutants near the surface. We also know that at this time, these combine with episodic events of stubble burning which is also concentrated around these two-three weeks in November,” Dahiya said.
“We know that these will cause an increase in emission load as well as build up of pollution concentration,” he added.
Two things could have been done better, Dahiya told The Wire. “One, manage the stubble burning incidents slightly better than what we have currently done. And second, we could have taken systematic and comprehensive actions to reduce emissions load from all perennial sources such as transportation, industries, construction and power plants.”
It is only because we have failed in taking systematic actions to curtail pollution net sources around these times when the meteorology turns unfavourable and there are episodic events such as firecracker bursting and stubble burning, these episodes add to the existing pollution load and makes it hazardous. This year has been very very bad,” Dahiya said.
“We have also seen that the number of fire counts have reduced when compared to the past year,” added Dahiya. Data shows that fires have greatly declined in Punjab, and decreased in Haryana and Uttar Pradesh. In terms of prediction too, IITM’s Decision Support System estimates that the maximum contribution from stubble burning is around 35%, which was on November 1, said Dahiya.
“Over the last three days, we have seen around 22-25% coming from stubble burning,” he said over a telephonic interview.
Fallouts of not curbing perennial sources
“That means that it is a significant amount of stubble burning but not the reason for all the pollution we face today, or even firecrackers…what is behind the rest 75% of the pollution? It is the sources that are within Delhi, such as transportation, waste burning and construction, as well as other regional sources which includes power plants, heavy industries in Haryana-Punjab region as well. These things haven’t started last week or yesterday. They have been going on for years and we have failed to curb rising emissions from these sectors.”
For instance, the DSS shows that Jhajjar (in Haryana) contributes to about 5% pollution in Delhi and Sonipat. What’s happening in these districts that their contribution is as high as Delhi’s residential sector contribution or Delhi and peripheral industries – it is the fact that Jhajjar is home to two big power plants; one has installed efficient pollution control technology, the other hasn’t; and Sonipat is an upcoming big industrial hub, Dahiya pointed out.
“We have to reduce the emissions at those sources by either reducing their operation particularly in these serious situations,” Dahiya added. “And in the longer term, either shift to cleaner fuels or have state-of-the-art technology to trap emissions at source. There is no other way around it.”
He also highlighted that the lack of implementation of existing policies are a concern in this region.
“We might have good policies, good guidelines, good regulations on paper, some have been diluted and delayed…but there is very little actual implementation of good directions to curtail emissions at source and that is what is needed,” Dahiya told The Wire.
The pollution level will not decrease drastically, but still remain between 250-300 in AQI throughout winter. This will be the case at least till the next monsoon, Dahiya said. “Rains are the time when Delhiites or north Indians get slight relief from pollution. Even then we don’t breathe the air quality that complies with the WHO standards, we only reach near the Indian standards.”
Indeed, if you look at CPCB’s bulletin for November 18 closely, it’s not just Delhi that is choking on bad air. The air quality in Gurugram is also “Severe”, at an AQI of 469; so is Noida (AQI of 423). The AQI of Bahadurgarh in Haryana, around 30 km northwest of Delhi, is also in the “Severe” category, at 453; so is Bhiwadi in Rajasthan, around 60 km southwest of Delhi, with an AQI of 447. Churu in Rajasthan has an AQI of 401; Dharuhera in Haryana has an AQI of 447. Air quality in Ghaziabad and Hapur in Uttar Pradesh is also “Severe”, at an AQI of 438 and 431 respectively. Sonipat, which Dahiya highlighted in his conversation with The Wire, is also under the “Severe” air quality category as on November 18, with an AQI of 430.
SC asks why GRAP stages not implemented earlier
The Supreme Court in its hearing on Monday said, “The approach adopted by the Commission seems to be that it waited for improvement of the AQI and, therefore, the implementation of Stages III and IV of the GRAP was delayed.”
“This is an entirely wrong approach. In anticipation of the AQI crossing the threshold limit, it is the duty of the Commission to start immediate implementation of Stages III and IV of the GRAP, as the case may be. The commission cannot wait for the improvement of the AQI.”
The court also mandated that Stage IV of the GRAP should continue even if the AQI goes below 450, and continue to do so till the commission receives directions from the court to stop.
India AQI vs US AQI
Screengrab from IQAIR.
Social media is rife with individuals and news houses sharing different values of Delhi’s air quality. Some quote the Indian Air Quality Index while others quote the AQI listed by IQAIR, a Swiss website that provides real time air quality reports and pollution forecasts. While the IQAIR’s rankings for the cities with the highest levels of pollution can be compared within its dataset, the AQI that IQAIR quotes is the AQI measured as per standards set in the United States. This is not directly comparable with the AQI or categories provided by the CPCB due to two reasons: first, the data that is used to calculate the corresponding AQIs are different; and second, both the AQIs categorise different levels of air quality differently.
Per the NAAQS 2019, the India AQI considers eight pollutants (PM10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia, and lead). But it is calculated only if data is available for at least three pollutants out of which one should be either PM2.5 or PM10.
The US AQI, meanwhile, has a separate AQI for five major air pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulphur dioxide and nitrogen dioxide.
The India AQI categorises air quality into six levels:
| AQI | Value of Index | PM2.5 levels (µg/m3) |
| Good | 0-50 | 0-30 |
| Satisfactory | 51-100 | 31-60 |
| Moderate | 101-200 | 61-90 |
| Poor | 201-300 | 91-120 |
| Very Poor | 301-400 | 121-250 |
| Severe | 401-500 | 250+ |
The US AQI on the other hand, as per the latest rules, makes the following classifications:
| AQI | Value of Index | PM2.5 levels (µg/m3) |
| Good | 0-50 | 0-9 |
| Moderate | 51-100 | 9.1-35.4 |
| Unhealthy for Sensitive Groups | 101-150 | 35.5-55.4 |
| Unhealthy | 151-200 | 55.5-125.4 |
| Very Unhealthy | 201-300 | 125.5-225.4 |
| Hazardous | 301+ | 225.5+ |
Hence Indian and US AQIs, as well as their categories, are not directly comparable.
However, as per IQAIR’s world rankings of air quality in cities – based on the US AQI calculations – Delhi’s AQI at 8:51 IST on November 18 was 1113, and in the “Hazardous” category as per US standards.
Delhi is currently the most polluted city worldwide. Kolkata is in third place in the ranking, with a US AQI of 204.
