Delhi's air quality sinks into 'very poor' days before Diwali

Delhi's air turned foul again this week, with the city's Air Quality Index climbing past 300 and into the dreaded ''very poor'' band. By Wednesday morning itread 377, well inside the range that health officials warn can damage lungs and worsen existing illness, with children and older residents hit hardest. Authorities have pulled the trigger on Stage II of the Graded Response Action Plan, a set of measures aimed at reining in dust, vehicle fumes and other pollution sources.

The slide stings because October was unusually kind. Delhi logged its cleanest October average in eight years, according to the BBC, before a storm dumped rain and stirred up stronger winds that scrubbed the air. Once the weather calmed, north-westerly winds returned, dragging smoke from burning fields in neighbouring Punjab and Haryana straight into the capital. Experts also point to falling temperatures and sluggish winds as the smog's accomplices.

The index tracks eight major pollutants, among them PM2.5 — particles roughly 30 times thinner than a human hair that burrow deep into the lungs. Anything between 301 and 400 counts as ''very poor''; above 400 is ''severe''. With Diwali just days away, the fear is that fireworks will shove those numbers higher still. Last year, Delhi woke to a toxic haze the morning after the festival, despite a court order pushing revellers toward less-polluting crackers.

On Monday, India's Supreme Court allowed the manufacture, sale and use of certified green firecrackers across Delhi and nearby areas — but only in tight slots. They can be burst from 06:00 to 07:00 and 20:00 to 22:00 local time on 7 and 8 November, during the Diwali weekend, and they are banned within 300m of hospitals, care homes, schools and other designated silence zones. Green crackers use tweaked chemical recipes meant to emit less, and must carry QR codes so buyers and officials can check who made them and whether they are certified.

Good luck policing that. The court itself acknowledged that ordinary firecrackers have kept showing up disguised as green ones, even when a full ban was in place. It has now told police to patrol sales areas, run random QR-code checks and seize illegal stock. Restrictions on firecrackers have come and gone for years, including outright bans on making, selling and using them, and enforcing those has always been a slog. When pollution turns especially brutal, Delhi has also rolled out hybrid schooling, work-from-home days and curbs on certain vehicles.

Delhi isn't choking alone. Mumbai, India's financial hub, clocked an AQI of 322 on 24 October — also ''very poor'' — blamed on weak winds, construction dust, garbage burning, firecracker emissions and pollution drifting in from nearby regions. Coastal breezes have since done their job: the city recorded a ''satisfactory'' 89 on Wednesday, while neighbouring Navi Mumbai sat at a ''moderate'' 118 after nearly two weeks of smog that residents documented all over social media.