On October 26, cities in Tamil Nadu and Andhra Pradesh were highlighted as some of the most polluted urban areas globally, with air quality levels surpassing those of Delhi. Data from AQI.in, accessed at 1:00 pm IST, revealed that Chengalpattu in Tamil Nadu ranked third worldwide, with an Air Quality Index (AQI) of 319, categorised as severe. Chennai followed closely in fourth place, recording an AQI of 303.

Several cities in Andhra Pradesh, including Nellore, Tirupati, Eluru, and Machilipatnam, also appeared among the 15 most polluted cities on the list. In addition, cities in Uttar Pradesh, such as Kanpur, Sitapur, Lucknow, and Prayagraj, were noted for their high pollution levels. The Indonesian city of Sampit topped the global rankings with an AQI of 410.

The rankings provide a significant insight into the severity of air pollution in regions beyond India’s well-known polluted areas. However, they do not imply that southern India consistently experiences worse air quality than Delhi throughout the year.

Factors Contributing to High AQI in Southern Cities

Several factors may explain the elevated AQI levels in southern cities, including the interplay of local emissions and prevailing weather conditions that facilitate pollutant accumulation. Urban air quality can be adversely affected by traffic emissions, industrial activities, construction dust, and other combustion-related pollutants.

Tamil Nadu’s industrial and urban corridors, particularly around Chennai and Chengalpattu, present multiple sources of potential pollution. In Andhra Pradesh, cities like Nellore, Eluru, and Tirupati face similar challenges from traffic, industrial emissions, and construction activities.

A Climate Trends analysis revealed that Chennai’s air quality deteriorated in 2025, with PM2.5 concentrations increasing across all seasons compared to 2024. The study, titled “Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities: Implications for NCAP Phase-III”, indicated a notable rise in winter PM2.5 levels, which escalated from 37.8 to 45.7 micrograms per cubic metre. In summer, concentrations increased from 21.3 to 23.9 g/m, while post-monsoon levels rose from 34.1 to 36 g/m.

Comparative Analysis of Air Quality in Delhi

Delhi’s air quality is often linked to winter smog, characterised by lower temperatures, reduced wind speeds, and temperature inversions that trap pollutants near the ground. Contributing factors include emissions from vehicles, industries, construction, and crop-residue burning. However, these conditions do not uniformly affect all cities or at the same time.

On October 26, the AQI.in data indicated that some southern cities experienced a more acute pollution episode, while Delhi’s position in the global rankings can fluctuate frequently. A separate report from the Central Pollution Control Board recorded Delhi’s AQI at 164 at 7:05 am on the same day, categorised as moderate. This figure cannot be directly compared with AQI.in data unless the methodologies and monitoring periods align.

It is essential to differentiate between a city’s ranking and its overall pollution burden. A city may temporarily appear on the list of the world’s most polluted locations due to a local spike, while another city with consistently high pollution may rank lower at that specific moment. The data from October 26 highlights that air pollution is not solely an issue for Delhi and the Indo-Gangetic Plain; southern cities also face significant pollution challenges that warrant attention.

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