As India celebrates Diwali, the air quality in several cities has deteriorated, including the AQI of India's cleanest city, Indore. The AQI in Indore breached the 400 mark in Friday, and the city has attained the “severe” category in Madhya Pradesh's financial capital.

According to the State Pollution Control Board data, the AQI in the city's Chhoti Gwaltoli area was pegged at 404 at noon, while the PM 2.5 (particulate matter) average was recorded at 255.26. The average level of PM 10 in the city was 318.08.

According to news agency PTI, the Chhoti Gwaltoli is a densely populated area of the city that sees heavy vehicular movement.

ALSO READ: Devender Singh Rana Last Rites: J-K CM Omar Abdullah, LG Manoj Sinha Attend BJP Leader's Funeral In Jammu | Watch

Dilip Vaghela, who is an environment expert and former official of the  State Pollution Control Board, told PTI, “The city started with loud Diwali fireworks from Thursday morning, which continued till late night. The situation continued in many areas on Friday also. This is the main reason for the air quality in the city reaching the severe category.”

The expert added that the city's air quality usually remains in the "satisfactory" (AQI 51-100) category.

According to the India Meteorological Department, the wind speed in the city was recorded at zero km per hour at 08.30 am on Friday. He also added that due to the calm winds, pollutants could not get scattered here and there and settled in one place, leading to the worsening of the air quality in the city.

According to news agency PTI, quoting the study by Clean Air Catalyst, a global coalition working to improve air quality, vehicular pollution and road dust are the highest contributors (70 per cent) to the deterioration of air quality in the city in normal times.

As per the MET department, an AQI between 0 and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor”, and 401 and 500 “severe”.

ALSO READ: Bhavish Aggarwal Shares Ola Diwali Celebration Video; Kunal Kamra Takes 'Service Station Dikhao' Potshot

On the ground, however, Indore has been a model city for waste management. In January, it was ranked as the cleanest city in India for the seventh year in a row under the Centre's annual Swachh Survekshan Awards.