Looking beyond AQI: How Indian cities compare with others worldwide

Indian cities’ air pollution was even higher than the WHO set standards and worse than most cities even on the days pollution was at its lowest

In 2015, the government’s introduction of the National Air Quality Index (AQI) was considered a significant move. India, dealing with severe air quality concerns, was reliant on the US Air Quality Index measurement. But the US measure did not address the air quality standards in India. The Indian measure was much stricter—measured on a scale of 500 (the US tops at 420)—and also included measurement of lead and ammonia, which the US AQI did not.  

While AQI measures have served as an essential barometer to assess air quality, they do not relay the complete picture. The scale of India’s air quality problem gets obscured when considering AQIs.

An analysis of India’s air quality data over the last 30 days shows how problematic Indian cities’ air quality is in relation to WHO standards and other cities worldwide.

WHO standards

In 2005, the World Health Organisation (WHO) set up air quality guidelines that prescribed levels for 6 different categories that the WHO wanted countries to achieve. The body had set the PM2.5 levels at 25 microgram/cubic metre (mu/m3) for a 24-hour average, and the annual target was a much lower 10 microgram/cubic metre. Similarly, for PM10, the target was set at 50 mu/m3 for 24 hours average and that for Nitrous Oxide was set at 20 mu/m3 and sulphur dioxide at 50 mu/m3.

The WHO subsequently revised these standards earlier this year, reducing the PM2.5  concentration to 15 mu/m3 for daily average emissions.

While the Indian AQI has not incorporated the new revised standards, analysis of last month’s data shows that cities could not even achieve the 2005 targets. While on one day, October 18, Delhi’s PM2.5 concentration was lower than 25, it breached the 25 mu/m3 mark on most other days. On November 4, Delhi’s PM2.5 concentration was 14.6-times more than WHO prescribed levels in 2005.

Similarly, the PM10 concentration was 9.9-times more, and Nitrous Oxide (NO2) concentrations were 1.3-times higher. On November 7—the day with the lowest pollution levels in the last week—the PM2.5 concentration was still 9.4-times more than the 2005 set standards.

Comparison with cities

The WHO comparison only illustrates how far Indian cities are from achieving the WHO set guideline. On the other hand, a city-wise comparison shows the extent of the problem and livability with other cities. Even when air quality was at its best across all cities last month, Mumbai still had the worst PM2.5 concentration among the 14 cities considered for this analysis, and Delhi ranked among the top-5.

In terms of PM10 concentration, Delhi, on its best day of air quality, had 1.3-times higher PM10 particles per cubic metre than the next most polluted city (Dubai). In terms of Nitrous Oxide (NO2), Sulphur Dioxide (SO2) and Carbon Monoxide (CO) emissions, even though the levels in the national capital were lower than WHO set emission standards, they were still the highest among all cities.

On the worst day, PM2.5 concentration in Delhi was 1.3-times higher than the second-worst polluted city and almost 4-times more than the third polluted city. The PM 10 concentration was 3-times higher than the second most polluted city. But NO2 and SO2 emissions were lower than in Los Angeles, US and Johannesburg, South Africa, respectively.