Cities in Tamil Nadu and Andhra Pradesh featured prominently among the world's most polluted urban centres on Monday, October 26, with several recording air quality levels worse than those in Delhi, according to AQI.in data accessed at 1:00 pm IST.Chengalpattu in Tamil Nadu ranked third globally, with an Air Quality Index (AQI) of 319, classified as severe on the displayed index. Chennai followed at fourth place with an AQI of 303.

Nellore, Tirupati, Eluru and Machilipatnam in Andhra Pradesh also featured among the 15 most polluted cities on the list.Kanpur, Sitapur, Lucknow, Prayagraj and other cities in Uttar Pradesh were also among the highest-ranked locations, while Sampit in Indonesia topped the list with an AQI of 410.The rankings offer a striking snapshot of how air pollution can become severe far beyond India's traditional pollution hotspots. But they do not necessarily mean southern India has worse air pollution than Delhi throughout the year.

WHY ARE SOUTHERN CITIES RECORDING SUCH HIGH AQI?One possible explanation is the combination of local emissions and weather conditions that allow pollutants to accumulate.Traffic exhaust, industrial activity, construction dust, road dust and emissions from other combustion sources can all contribute to poor urban air quality. Tamil Nadu's industrial and urban corridors, including areas around Chennai and Chengalpattu, have multiple potential pollution sources.

In Andhra Pradesh, traffic, industrial emissions, construction and other local sources may contribute to pollution in cities such as Nellore, Eluru and Tirupati.Chennai’s air quality worsened in 2025, with PM2.5 concentrations rising across all seasons compared with 2024, according to a Climate Trends analysis of major Indian cities.The study, “Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities: Implications for NCAP Phase-III”, found the sharpest increase during winter, when average PM2.5 levels rose from 37.8 to 45.7 micrograms per cubic metre.Summer concentrations increased from 21.3 to 23.9 g/m, while post-monsoon levels climbed from 34.1 to 36 g/m. Monsoon pollution remained relatively stable, edging up from 21.2 to 21.5 g/m, signalling growing air-quality concerns.Weather also plays a major role.

Wind speed and direction influence how quickly pollution disperses, while atmospheric stability can allow emissions to build up near the surface.A temporary spell of stagnant air can push a city's AQI sharply higher, even if its longer-term pollution levels are lower than those of another city.WHY IS DELHI'S AIR BETTER TODAY?Delhi's pollution is often associated with winter smog, when falling temperatures, weaker winds and temperature inversions trap pollutants close to the ground. Emissions from vehicles, industries, construction and crop-residue burning can add to the burden.But these conditions do not affect every city equally or at the same time.

The AQI.in snapshot shows that some southern cities experienced a sharper pollution episode on October 26, while Delhi's position in a global ranking can change with the hour.A separate report citing the Central Pollution Control Board put Delhi's AQI at 164 at 7.05 am on Monday, in the moderate category. This is not directly comparable with the AQI.in figures unless the index methodology, averaging period and monitoring coverage are the same.There is also a crucial distinction between a city's ranking and its overall pollution burden.A city can briefly enter the world's most polluted list because of a local spike, while another city with persistently high pollution may rank lower at that particular moment.The October 26 data indicates that India's air pollution problem is not confined to Delhi and the Indo-Gangetic Plain.

Southern cities, too, can experience hazardous episodes that deserve attention.However, the snapshot does not establish that Tamil Nadu and Andhra Pradesh have become more polluted than Delhi overall.- Ends