CHENNAI: Chennai recorded a sharp rise in nitrogen dioxide (NO2) levels and witnessed localised air pollution hotspots this past winter, despite a stable citywide average, according to a new analysis by the Centre for Science and Environment (CSE).
The study, carried out from October 1, 2024, to January 31, 2025, shows NO2 concentrations surging across the city, with Manali recording a dramatic 3.8-fold increase from October to December and Alandur doubling its levels over the same period.
Alongside this, Chennai’s seasonal PM2.5 average held at 36 micrograms per cubic metre (µg/m³) — a modest 1.2% rise from the past three winters — yet specific areas saw significant pollution spikes, heightening health risks.
The CSE report, drawing from eight continuous ambient air quality monitoring stations (CAAQMS) and processed via USEPA methodology, reveals stark local variations. Velachery logged the highest daily PM2.5 peak at 193 µg/m³, while Alandur and Manali topped the list of polluted zones with seasonal averages of 47 µg/m³ each.
Winter PM2.5 levels at monitoring stations exceeded annual averages by 3-40%, with Arumbakkam, Royapuram and Perungudi jumping over 35% above their yearly norms. Alandur endured 14 days of ‘poor’ and ‘very poor’ Air Quality Index (AQI) ratings, followed by Velachery with seven. The city’s peak PM2.5 day hit 119 µg/m³ on October 31, 2024, down 19% from past winters but still concerning.
Chennai’s NO2 crisis mirrors trends in other mega cities, amplifying the multi-pollutant challenge. Mumbai’s Byculla saw NO2 soar 5.7 times, while Kolkata’s Victoria recorded a 6.4-fold spike, peaking at 84 µg/m³ in December.
In comparison, Delhi’s Anand Vihar logged a 71% NO2 surge, hitting 167 µg/m³, and Hyderabad’s Zoo Park reached 93 µg/m³. Chennai’s PM2.5 hotspots also align with broader patterns: Anand Vihar averaged at 227 µg/m³, Kolkata’s Ballygunge hit 80 µg/m³, Mumbai’s Deonar matched that at 80 µg/m³ (60% above its 50 µg/m³ city average), and Bengaluru’s RVCE reached 56 µg/m³ (51% over its 37 µg/m³ average).
These spikes, driven by stagnant winter conditions and rising vehicular emissions, are a cause of concern. While Chennai saw some relief — a 29% PM2.5 drop at Kodungaiyur — its escalating NO2 levels and persistent hotspots demand urgent action.
The city’s coastal advantage pales against Delhi’s landlocked 175 µg/m³ PM2.5 average and eight ‘severe+’ AQI days, but local exposures remain a pressing concern, necessitating targeted measures to curb emissions and safeguard public health, said Anumita Roychowdhury, Executive Director, Research and Advocacy, CSE.
Can’t breathe easy
Chennai’s winter PM2.5 average 36 µg/m³, just 1.2% higher than past three winters
PM2.5 levels soared 3-40% above annual averages
Alandur, Manali topped the charts with seasonal PM2.5 averages of 47 µg/m³ each
Alandur logged 14 days of ‘poor’ or ‘very poor’ AQI; Velachery followed with 7 days
Velachery’s PM2.5 jumped 37%, Alandur 10%, and Manali 5%
Kodungaiyur cut PM2.5 by 29%, while Perungudi saw a slight drop
Manali’s NO2 spiked 3.8 times from October to December; Alandur saw a two-fold rise