Understanding India's Pollution Limit: The 500 AQI Cap Explained

Sun Nov 16 2025 06:06:53 GMT+0200 (Eastern European Standard Time)

Why does India set its air quality index (AQI) cap at 500, despite readings showing much greater pollution? This article delves into the implications of this regulation and its impact on public health perception.

India's air quality index (AQI) is capped at 500, designed initially to prevent public panic. However, private monitoring systems often report levels exceeding 1,000, leading to confusion about which numbers to trust. Experts discuss the need for revising this outdated limit and highlight discrepancies with international standards.

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.

But 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.

In contrast, international organizations and portals don't impose such a cap, which is why we see numbers going much higher on global platforms.

Experts also note that there is a difference in defining hazardous air. The World Health Organization (WHO) guidelines classify PM2.5 levels above 15 micrograms per cubic metre in a 24-hour period as hazardous, while in India, the threshold is 60 micrograms.

According to experts, the air quality framework in India hasn't been comprehensively revised since 2009, and there are calls for recalibrating the scale based on the latest technology. Removing the upper cap is crucial, say experts, as most literature indicates health symptoms worsen as pollution levels increase.

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