According to the report for 2016 released by WHO on Thursday, India’s Tier 2 and Tier 3 cities, which have far poorer air quality monitoring systems, are already among the global cities with the highest levels of particulate matter (PM).

Gwalior, among the top five cities globally in terms of PM 2.5 levels, recorded an annual average of 176 micrograms per cubic metre (ug/m3) and Allahabad 170. The 20 global cities with the highest PM 2.5 levels included Patna and Raipur with 149 and 144 ug/m3, respectively.

In WHO’s last report released in 2014, about 25 Indian cities had higher air pollution levels than Beijing — earlier thought to be the city with the worst air in the world. Gwalior recorded 144 ug/m3 in the 2014 report, trailing Delhi’s 153 ug/m3 — the worst in the world that year. Cities like Kanpur, Ludhiana and Allahabad continue to feature among the top 20 cities with the highest PM 2.5 levels in the 2014 and 2016 reports. Asked if other Indian cities, which figure among the highest global contributors to PM 2.5 and PM 10, need to replicate steps taken by Delhi, one of the main authors of the study, Dr Sophie Germy, said, “A lot more needs to be done in India, and some steps need to be replicated. But even in some high-income cities, particulate matter remains a problem despite intensive monitoring and steps to control pollution.” Within India, the Central Pollution Control Board’s (CPCB) monthly air quality analysis (AQI) shows that cities like Agra, Raipur, Faridabad, Ludhiana and Patna report more poor air quality days than metropolitan cities like Delhi and Bengaluru. “Patna, Gorakhpur and Agra are reporting far more days in the very poor category than other Tier 2 and 3 cities. The dominant pollutant in these cities, even during summer months, is usually particulates, unlike cities like Delhi where pollutants like ozone and NO2 become dominant,” a CPCB scientist said. Increased construction, boom in industrial activity and sharp spikes in use of vehicles could be responsible for these trends, he said.