Why India's Air Quality Cap Defies Reality

Sun Nov 16 2025 06:06:33 GMT+0200 (Eastern European Standard Time)

India's air quality index, capping at 500, prompts confusion amid higher readings from private monitors, raising concerns about public health and data accuracy.

As millions in northern India grapple with hazardous air quality, the official air quality index (AQI) remains capped at 500, leading to confusion as international monitors report readings exceeding 600 and even above 1000. Experts suggest this threshold limits public awareness and urges for a review of the outdated system that fails to reflect the actual pollution levels affecting health. Calls for modernization of monitoring practices and removal of the cap are gaining traction amidst rising pollution concerns.

For millions across northern India, the November air tastes ashy, the sky looks visibly hazy and merely stepping outside feels like a challenge.

For many, their morning routine starts with checking how bad the air is. But what they see depends entirely on which monitor they use.

Government-backed apps like SAFAR and SAMEER top out at 500 - the upper limit of India's AQI (air quality index) scale, which converts complex data on various pollutants such as PM2.5, PM10, nitrogen dioxide, sulphur dioxide, carbon monoxide and ozone, into a single number.

But private and international trackers such as IQAir and open-source monitoring platform AQI routinely show far higher numbers, often shooting past 600 and even crossing 1,000 on some days.

This contradiction leaves people asking the same question every year: Which numbers should they trust? And why doesn't India officially report air quality beyond 500?

India's official air-quality scale shows readings above 200 pose clear breathing discomfort to most people on prolonged exposure.

Readings above 400 and up to 500 are classified as 'severe' and affect healthy people while also seriously impacting those with existing diseases.

The scale, however, does not go beyond 500 - a cap set more than a decade ago when the National Air Quality Index was launched.

So why was that threshold introduced?

'It was assumed that the health impact would be the same no matter how much higher it goes because we had already hit the worst,' says Gufran Beig, founder director of SAFAR.

He admits that the 500 cap was originally set to avoid creating panic as crossing that mark signalled an alarming situation requiring immediate mitigation.

But this approach effectively flattens the data - anything above 500 is treated the same on official monitors, even if the real concentration is far higher.

'International organisations and portals don't impose such a cap,' says Mr Beig. 'That's why we see numbers going much higher on global platforms.'

Beyond the artificially imposed threshold, there's also a difference in defining hazardous air.

For example, the World Health Organization (WHO) guidelines classify PM2.5 levels - particulate matter smaller than 2.5 micrometers - above 15 micrograms per cubic metre in a 24-hour period as hazardous, while in India, the threshold is 60 micrograms.

Experts say that globally, there's no universal AQI formula. US, China and the European Union each apply their own pollutant thresholds.

Then there is also a difference in the instruments used.

The Indian pollution control board uses Beta Attenuation Monitors (BAMs), which physically measure the mass of particles in the air and are calibrated to strict, standardized metrics for every reading.

In contrast, portals like IQAir rely on sensor-based monitors that utilize laser scattering and electrochemical methods to estimate the number of particles suspended in the air. However, these have not been government approved for accuracy.

According to Mr Pathak, India's air quality framework hasn't been comprehensively revised since 2009, and he, along with other environmental scientists and activists, calls for recalibrating the scale based on the latest technology.

In summary, India's AQI doesn't stop at 500 because the pollution stops there but because the system was built with a ceiling.