Delhi’s air quality deteriorated to the “very poor” category on Tuesday morning from “satisfactory” on Saturday, data from the National Air Quality Index by Central Pollution Control Board showed.

The national capital’s air quality index stood at 396 on Tuesday. On Saturday, it was at 57.

Air quality index between zero and 50 is considered “good”, 51 and 100 is “satisfactory”, while 101 and 200 is termed “moderate.” Air quality index between 201 and 300 comes under the “poor” category while 301 and 400 is defined as “very poor”, and 401 and 500 is “severe.”

The Central Pollution Control Board uses 24-hour average data to measure the air quality index. Meanwhile, data from the Ministry of Earth Sciences’ System of Air Quality and Weather Forecasting And Research, or Safar, which has real-time figures, showed the city’s air quality index at be “moderate” at 127 on Tuesday noon.

According to government data presented in Rajya Sabha on July 28, Delhi did not record a single “good” air quality day between January and June, reported PTI. However, the city recorded seven “satisfactory” and 47 “moderate” air quality days during the same period.

Delhi recorded 105 “poor”, 21 “very poor” and one severe air quality day between January and June, the data showed.

Owing to the increasing air pollution, production, storage, sale and use of firecrackers in the capital till January 1, 2023.

The Delhi government banned firecrackers between September and January last year as well to prevent air pollution.

Farmers from Punjab, Haryana and Uttar Pradesh burn the residue of their paddy harvest during this season since it is a cost-effective and time-saving measure to prepare the fields for the next sowing cycle. However, this practice results in increased levels of air pollution in large areas of North India.

Lower temperatures, wind speeds, and other factors such as industrial pollution add to the problem. Often, the air quality index drops around Diwali, when firecrackers are burst.