Delhi's air quality took a sharp plunge and entered the 'severe' zone on Friday, following night-long Diwali revelry when people set off millions of firecrackers and reduced a Supreme Court ban on their sale into a 'heap of ash'.
The pollution indicator of state-run System of Air Quality Forecasting and Research (SAFAR) turned a deep shade of brown, indicating 'severe' air quality in the city, which may affect healthy people and seriously impact those with existing respiratory or cardiovascular diseases.
The 24-hour rolling average of PM2.5 and PM10, ultrafine particulates which are upto 30 times tinier than the width of a human hair, were 424 and 571 micrograms per cubic metre (ug/m3) respectively, multiple times higher than the safe limits of 60 and 100.
The United States embassy's pollution monitor recorded 'hazardous' air quality with the index scoring an alarming 878, which the mission considers 'beyond its air quality index' (AQI), which ends at 500.
But unlike previous years, the run-up to Diwali festivities was much cleaner this time.
Even the Diwali evening was relatively quiet and promising, suggesting that the ban on sale of firecrackers in the Delhi-NCR imposed by the apex court has worked. This was captured by the Central Pollution Control Board which had Delhi's AQI (air quality index) at 319, which is considered 'very poor', for October 20.
However, since the figure was released at 5 pm, it could not quite record what followed thereafter.
As the clock ticked, frenzied celebrations picked up and noisy and relentless bursting of firecrackers continued till the wee hours, sending pollution graph off the charts.
The online indicators of pollution monitoring stations in the city glowed red, indicating a 'very poor' air quality as the volume of ultra fine particulates PM2.5 and PM10, which enter the respiratory system and manage to reach the bloodstream, sharply rose from around 7 pm on Thursday.
The line graphs of the the pollution data of the Delhi Pollution Control Committee (DPCC) stations were telling.
In station after station, the volume of PM2.5 and PM10 built up rapidly around 7 pm and peaked post midnight, soaring upto 10 times above the safe 24-hour limits.
For example, the RK Puram monitoring station recorded PM2.5 and PM10 at 878 and 1,179 micrograms per cubic metre at around 11 pm. The monitors stopped working after midnight, suggesting that the pollutants had gone through the roof.
While it is difficult to quantify the immediate effect of the ban on firecrackers, residents across the national capital felt the beginning was promising with neighbourhoods reporting much lesser noise and smoke till about 6 pm, compared to the previous years.
But as the festivities picked up, the faint echos of crackers started growing louder.
The situation was similar, if not worse, in the neighbouring regions of Delhi such as Gurugram, Noida and Ghaziabad, where crackers were burst as usual, raising question marks on the efficacy of the administration in enforcing the apex court's ban.
However, if one goes by SAFAR's forecast, post-Diwali air will not be as poor as last year, which was the worse in at least three decades. It said a host of favourable meteorological conditions were helping prevent smoke-filled air from the agricultural belt of Haryana and Punjab from entering the national capital.
Had that not been the case, Delhi's air, already saturated with pollutants, would have turned deadlier.
The Supreme Court-appointed Environment Pollution Prevention and Control Authority (EPCA), which is empowered to enforce the Graded Response Action Plan (GRAP) to combat air pollution in Delhi-NCR, kicked off a series of preventive measures on October 17.
Measures under the GRAP's 'very poor' and 'severe' categories, which include a ban on diesel generator sets, have come into effect and will remain in force till March 15.
All Photographs: Kamal Singh/PTI Photo