Delhi's air quality started worsening just ahead of Diwali as on November 3, the air quality in Delhi entered the 'very poor' category for the first time this season. The overall air quality index (AQI) of the city was 303. 

As expected, the Air Quality Index (AQI) surged to 463 on the occasion of Diwali (November 4). A thick blanket of smog shrouded the skies of Delhi, as several people complained of an itchy throat and watery eyes.

In recent times, Supreme Court has come down heavily on the bursting of firecrackers during Diwali. The apex court has banned the bursting of firecrackers saying it causes pollution. However, the court recently clarified that there is no blanket ban and only those crackers containing Barium salts are prohibited.  

Delhi govt headed by Arvind Kejriwal had put a complete ban on the sale and use of firecrackers. But with air quality reaching hazardous levels post-Diwali, the govt deployed 114 tankers to spray water across the city in a bid to reduce the mounting levels of air pollution and settle the dust.

On November 12, Delhi's AQI was 390. And the visibility in Delhi will remain poor for the next three days due to fog and smog, said Senior Scientist of the India Meteorological Department (IMD). A layer of smog shrouded Delhi-NCR as the air quality in Delhi continued to remain under the 'very poor' category.

World Health Organization (WHO) released a revised Global Air Quality Guidelines in September, announcing more stringent limits for six pollutant categories —particulate matter (PM), ozone (O3), nitrogen dioxide (NO2) sulfur dioxide (SO2) and carbon monoxide (CO). 'Air pollution is a threat to health in all countries, but it hits people in low- and middle-income countries the hardest,' said WHO Director-General Tedros Adhanom Ghebreyesus at the virtual launch of the guidelines.