CHENNAI: Chennai’s air quality deteriorated in 2025, with PM2.5 pollution levels rising across all seasons compared to 2024, according to a new analysis examining pollution patterns across major Indian cities.
The study, “Meteorology-Driven Persistence of PM2.5 Pollution in Indian Cities: Implications for NCAP Phase-III,” by Climate Trends, shows that seasonal mean PM2.5 concentrations in Chennai increased consistently in 2025, signalling emerging air-quality concerns even in a city generally considered cleaner than most Indian metros.
Data from the study show that winter (December–February) PM2.5 levels rose sharply from 37.8 micrograms per cubic metre (µg/m3) in 2024 to 45.7 µg/m3 in 2025, marking the steepest increase. Summer (March–May) concentrations also climbed from 21.3 µg/m3 in 2024 to 23.9 µg/m3 in 2025, while the monsoon season remained relatively stable, increasing marginally from 21.2 µg/m3 to 21.5 µg/m3. During the post-monsoon period (October–November), the seasonal mean rose from 34.1 µg/m3 in 2024 to 36.0 µg/m3 in 2025.
Monthly trends further reinforce this pattern. In 2024, January recorded the highest monthly mean PM2.5 level at 46.7 µg/m3, followed by November at 39.6 µg/m3 and December at 31.0 µg/m3. The lowest level was recorded in May at 16.5 µg/m3.
In contrast, 2025 saw higher winter and post-monsoon pollution, with December registering 53.7 µg/m3 — the highest monthly average across both years. January recorded 46.8 µg/m3 and November 43.5 µg/m3.
Experts say meteorological conditions play a crucial role in shaping pollution patterns across Indian cities. Sagnik Dey, head of the Centre for Atmospheric Sciences at IIT Delhi, said ventilation efficiency is a key factor influencing PM2.5 levels. The study calls for season-specific targets and meteorology-based interventions under the National Clean Air Programme to address rising pollution trends.