New Delhi:

Delhi’s air quality remained severely toxic on Tuesday, with the overall air quality index (AQI), which measures pollutants, spiked to 494. According to the Central Pollution of Control Board (CPCB) data, most of the monitoring stations in the national capital recorded an AQI of 500, forcing all schools across Delhi-NCR to go online. However, at the same time, the international monitoring app, IQAir, showed Delhi’s AQI at 1,600.

Why Delhi’s AQI Was 494 but IQAir showed 1,600?

All countries have different standards for measuring the air quality index. It varies from country to country, depending on pollutants and their measuring scale. In India, the scale of PM 2.5 is 60, while in some countries, that have adopted the World Health Organisation (WHO) standard, is five or ten.

Similarly, India’s AQI has been capped at 500 – which means that an air quality index bigger than that is a big warning that the level of pollution is extremely severe.

According to the CPCB, an AQI between 0 and 50 is considered good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor, 401 and 450 severe, and above 450 to 500 is severe-plus.

On the other hand, IQAir – which is based on the US model developed by the country’s Environment Protection Agency, has ‘hazardous’ as the highest level of scale (over 500). 

How do international agencies monitor India’s AQI?

International agencies such as IQAir have installed sensors at some places across Delhi-NCR. 

However, there is no clear information on whether the sensors have been installed at the right place with the standard equipment.

Which monitor’s AQI should we follow?

While there is no particular right or wrong monitor, in India, citizens should consider the AQI released by the CPCB – which has 40 stations across Delhi-NCR for assessing pollution. 

Delhi’s air remains toxic, GRAP 4 imposed 

As the air quality in Delhi-NCR entered the ‘severe plus’ category on Monday, the Delhi government imposed Stage 4 of the Graded Response Action Plan (GRAP), an anti-pollution plan – in addition to the first three stages.

Under this, a ban has been imposed on Delhi-registered BS-IV or older diesel medium and heavy goods vehicles. All trucks and light commercial vehicles registered outside Delhi will not be allowed to enter the national capital, except for those carrying essential commodities or providing essential services.

Additionally, public and private offices have been asked to work at 50 per cent capacity and the rest have been recommended to work from home. All schools have been either closed or gone online.

New Delhi:

A thick layer of smog – a toxic blend of smoke and fog – enveloped the Delhi-National Capital Region (NCR) this morning as the air quality index (AQI) plummeted to the “severe-plus” category, forcing authorities to announce stricter pollution control measures.

Smog also affected visibility in the national capital which various airlines said could delay flight schedules. Visibility at Palam dropped to 150 metres at 7 am.

#6ETravelAdvisory: Fog is currently affecting visibility in Delhi, which may result in slow moving traffic and delays in flight schedules. We recommend allowing extra travel time and checking flight status before starting your journey https://t.co/rpnOvAOxQl. Safe travels!

— IndiGo (@IndiGo6E) November 17, 2024

Kind attention to all flyers!#Fog#FogAlert#DelhiAirportpic.twitter.com/QRx6v26Ral

— Delhi Airport (@DelhiAirport) November 18, 2024

According to the real-time data provided by the System of Air Quality and Weather Forecasting and Research (SAFAR), the AQI in Delhi was recorded at 481 at 6 am, the worst so far this season. Officials said it was due to “unfavourable” meteorological conditions in Delhi-NCR.

An AQI between 0 and 50 is considered good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor, 401 and 450 severe, and above 450 severe-plus.

The Centre’s air quality panel has invoked stricter pollution control measures for the Delhi-NCR under Stage 4 of the anti-pollution plan Graded Response Action Plan (GRAP), which have come into effect from 8 am. This is in addition to the preventive actions announced under Stage 1, Stage 2 and Stage 3 of GRAP already in force.

The GRAP for Delhi-NCR is divided into four stages of air quality: Stage 1 for “poor” air quality (AQI ranging from 201 to 300), Stage 2 for “very poor” air quality (AQI from 301 to 400), Stage 3 for “severe” air quality (AQI from 401 to 450), and Stage 4 for “severe-plus” air quality (AQI above 450).

The panel – Commission for Air Quality Management (CAQM) – has urged the public, particularly children, senior citizens and those with respiratory, cardiovascular, cerebrovascular or other chronic diseases, to stay indoors.

GRAP 4 In Delhi As Air Quality Worsens

Under Grap 4, no trucks will be allowed into Delhi except for those carrying essential items or using clean fuel (LNG/CNG/BS-VI diesel/electric). Non-essential light commercial vehicles registered outside Delhi will be prohibited, except for EVs and CNG and BS-VI diesel ones and those carrying essential items.

Delhi-registered BS-IV or older diesel medium and heavy goods vehicles are banned, except for those in essential services.

In-person classes have been suspended for all except for students in classes 10 and 12.

All construction activities, including highways, roads, flyovers, power lines, pipelines and other public projects, have been suspended.

Public and private offices in Delhi-NCR have been recommended to work at 50 per cent capacity, with the rest working from home. Work-from-home options may also be introduced for central government employees.

State governments could also close colleges, limit non-essential commercial activities and implement odd-even vehicle rules.

Around 38% of the pollution in the national capital this year has been caused by stubble burning or farm fires in the neighbouring states of Punjab and Haryana.

Delhi grapples with smog each winter as cold air traps dust, emissions and smoke from illegal farm fires.