India's national capital and its environs were enveloped in a toxic haze and acrid stench of smoke on Thursday evening as large numbers of revelers violated the ban on firecrackers and police looked the other way to inflict a health crisis on their fellow citizens that would be far more toxic had it not been for the providential winds on Friday that helped blow away the smoke.

Across the National Capital Region (NCR), what began as a staccato of bangs and bangs late in the evening turned into a crescendo of whistling rockets, thunderous airbursts and relentless smoke-belching sparks from anars and charkhis that continued well past midnight. The Air Quality Index (AQI) was at 328 at 4pm before the start of Thursday's celebrations, classified as “very poor” and remained stable until around 9pm, after which it began to steadily deteriorate: 330 at 10pm, 338 at midnight, 347 at 3 a.m. Friday and 362 at 9 a.m. After 9 a.m. the AQI started improving and was 354 at noon, 339 at 4 p.m. and 314 at 10 p.m.

However, these numbers were all 24-hour averages. In real time, PM2.5 levels in the city increased a staggering 15-fold in some parts of the city, reaching levels of over 1,800 µg/m³ in certain residential areas. The World Health Organization sets the safe limit of PM2.5 exposure at 15 µg/m³, while India's national air quality standards set it at 60 µg/m³.

By Friday afternoon, the worst of the pollution appeared to have been swept away by strong winds and warm temperatures. Meteorological circumstances that were unusual for this time of year, but which gave the city of 20 million inhabitants a stroke of luck.

“We had steady winds throughout Diwali day and on Friday too. The wind speed was 12-16 km/h until 6 p.m. on Thursday. “It dipped slightly but remained between 3 and 7 kmph throughout the night and rose again to around 10 kmph when the sun came out on Friday,” said an India Meteorological Department official, who was not named Another climate expert described this improvement as nothing more than “luck with the weather.”

It wasn't just the sights and sounds on Thursday evening that demonstrated the brazen disregard for the fireworks ban.

Analysis of real-time pollution monitoring data by HT shows in detail how concentrations of PM2.5, ultrafine particles that mainly make up smoke, shot up in the evening: At Nehru Nagar station, adjacent to Lajpat Nagar, hourly average PM2.5 concentrations rose from 101 µg/m³ to a whopping 898 µg/m³ at 11 p.m., almost nine times higher. In Anand Vihar, adjacent to the residential colonies of Vivek Vihar, the peak level at 1 am was 992 µg/m³, more than seven times the 135 µg/m³ recorded at 6 pm.

With immediate measurements, these numbers reached even more alarming levels: 1,853 µg/m³ at Vivek Vihar and 1,527 µg/m³ at Nehru Nagar.

That these spikes were due to firecrackers is clear when one considers readings in Narela and Najafgarh, both industrial areas that were empty as people returned home to celebrate Diwali. In Najafgarh, the peak was around 247 µg/m³ and in Narela it was around 260 µg/m³ – both stations recorded 80-90 µg/m³ in the evening, making the rise the most moderate in the city.

India classifies the safe limit for PM2.5 exposure at no more than 60 µg/m³.

Other data also suggested that there were widespread violations of the fireworks ban. The Delhi Pollution Control Committee (DPCC) said that out of its 31 environmental noise monitoring stations, 22 recorded higher decibel levels this Diwali compared to last year. The highest decibel levels this Diwali were recorded at Karol Bagh in central Delhi – an average of 88.7 dB (A), about 5% higher than the average level of 84.5 dB (A) recorded last Diwali.

The Delhi Fire Department also said it received the highest number of calls for fire-related incidents since records began in 2012, at 280.

The flouting of the fireworks ban raised questions about the effectiveness of environmental regulations in a city that regularly ranks among the world's most polluted capitals. When contacted, an official from the Environment Ministry said that enforcement of the ban rested with the Delhi Police. “We have appealed to people not to burst crackers and to report incidents on 112 and 1090. The police were then responsible for taking appropriate action,” the official added.

The Delhi Police did not comment on the mass violation of the fireworks ban.

HT sent messages to several senior police officers, including the Delhi Police spokesperson and deputy commissioners of police (DCPs) of all 15 police districts, seeking data and their response to action taken against fireworks ban violators. They did not respond until press time.

What helped was simply the weather. “We were lucky in the sense that we have seen this in some previous years when wind speeds were low and pollutants hung in the air for several days. When the wind is strong, the pollution spreads within a few hours and then again there are local sources that increase the pollution,” said Mahesh Palawat, vice president at Skymet Meteorology, predicting a similar wind speed on Saturday but a decrease on Sunday .

Environmental experts pointed out that relying on favorable weather conditions is a dangerous gamble.

“October was a warmer month and Diwali day recorded fairly good wind speeds. The pollution levels on Diwali night, which reached severe levels, did not last for very long,” said Anumita Roychowdhury, executive director of research and advocacy at the Center for Science and Environment (CSE), pointing out that the peak levels of air pollution in the Diwali night was actually in serious territory.

“The firecracker burst demonstrates that while firecracker command and control measures have established the conditions for compliance, their success requires a high level of public awareness of the health risks posed by excessive and short-term exposure to such pollution.” , she added.