On Tuesday morning, the national capital Delhi was enveloped in thick smog as air quality plunged to perilous levels, with several parts of the city registering readings in the “severe” category. According to the Swiss air-quality technology firm IQAir, Delhi stood as the most polluted major city globally on October 21 2025. 

Data shows fine particulate matter (PM2.5) at concentrations more than 15 times the WHO’s guideline, with some readings reportedly over 59 times the limit. Monday’s Diwali fireworks, combined with cooler calm weather and lingering crop-burning emissions from nearby states, pushed pollution further into the hazardous range.

Local monitoring stations recorded AQI values above 400 in several zones, marking them as “severe” and signalling immediate health risks for residents — especially children, the elderly and those with respiratory conditions. Authorities have urged people to stay indoors and avoid strenuous outdoor activity as the smog persists. 

With the seasonal “smog window” now open for Delhi, the recurring winter spike in pollution underscores the urgent need for stronger enforcement of emissions rules, better regional coordination and long-term air-quality planning.