New Delhi: Monsoon rain may offer Delhi temporary relief from air pollution, but it can’t stop emissions driving the city’s poor air quality, states a study by Centre for Science and Environment (CSE).Monsoon: Delhi’s baseline air quality (2026), a study by CSE’s Anumita Roychowdhury and Sharanjeet Kaur, examined air quality during April-Aug 2026 to understand how much monsoon actually improves Delhi’s pollution levels. It argues that rainfall provides a natural “washout”, but pollution quickly returns once the rain stops.Delhi’s average PM2.5 concentration fell from 60.2 micrograms per cubic metre in April-May to 40.2ug/m3 during the monsoon period in June-Aug, a decline of about 33%. But the improvement did not translate into consistently clean air. Of the 92 monsoon days, only one had good air quality, while 53 days — 57.6% — were moderate and three poor.The study analysed six separate rain events during the monsoon to find that before rain, average PM2.5 was 40.6ug/m3, which fell to 32.7 during rain, but rose to 36.2 within 24 hours and 45.1ug/m3 after 48 hours. The finding highlights a central problem for Delhi: rain can remove pollution from the air, but it cannot prevent new pollution from being emitted. As soon as the rain stops, continuing emissions from vehicles, industries, waste burning and power generation can rebuild pollution levels.The problem also extends beyond particulate pollution. The study found that when PM2.5 falls, gaseous pollutants can become prominent drivers of the daily air quality index. Ground-level ozone was prominent on 20% of the monsoon days, while nitrogen dioxide was prominent on 10% and carbon monoxide on 7% of these days. The report links these pollutants to emissions from vehicles, diesel generators and industries.The authors warned that the end of the monsoon removes this natural cleaning mechanism just as Delhi enters weather conditions that can trap pollution. Relying on seasonal rainfall or temporary winter restrictions is, therefore, inadequate, they said.“While monsoon rains bring temporary relief, they only mask the underlying crisis. The fact that even heavy rainfall failed to bring consistent good air quality and that pollution rebounded within 48 hours during dry spells shows that our baseline emissions remain dangerously high. As we enter winter, we are starting from a baseline where continuous, elevated emissions will inevitably trigger severe seasonal spikes,” said Roychowdhury, executive director of research and advocacy at CSE.“Only sustained, year-round, airshed-wide emission reductions can secure cleaner air,” the report states, calling for action across transport, industry, waste management, electricity and other sectors across NCR.
