Delhi's pollution remains severe as authorities warn of further deterioration due to stubble burning

Delhi's pollution level remained in the 'severe' category for the second day, even as authorities warned that the already toxic situation caused by smoke from fireworks is likely to aggravate further due to intensified stubble burning in neighbouring states.

The overall air quality index (AQI) was recorded at 421 which falls in the 'severe' category, according to data from the Central Pollution Control Board (CPCB).

The Centre-run System of Air Quality and Weather Forecasting And Research (SAFAR) recorded the AQI at 453.

Faridabad, Ghaziabad, Noida and Greater Noida recorded air quality in the "severe" category, while Gurgaon registered "very poor" air quality. In NCR, the highest AQI was recorded in Faridabad at 460.

SAFAR said the city's air quality has "improved significantly" since Thursday, but warned that the already toxic situation caused by smoke from fireworks is likely to aggravate further due to intensified stubble burning in neighbouring states.

"As per satellite images, heavy fire counts were recorded in the last 24 hour and the latest SAFAR model results show a movement of cold front carrying heavy air mass towards Delhi region," SAFAR said.

Elaborating on it, the weather forecast system said the air in the surrounding stubble-burning areas is already heavy due to increased moisture and pollutants.This heavy air will travel towards Delhi, where a similar situations exists, in the next 24 hours. This combined effect might add to the pollution woes.

"There is a possibility that the wind may pick up at the upper level, late in the night and push the level of pollution and keep it in severe zone tomorrow with intensified fog which will further trap the pollutants," it said.

Twenty six areas in Delhi recorded 'severe' air quality, while seven areas recorded 'very poor' air quality, according to the data of the CPCB.

On Friday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded at 303 gm-3, six times the permissable limit.

The PM10 (particles in the air with a diameter of less than 10 micrometres) level was recorded four times the permissable limit at 440 gm-3, according to SAFAR.

India's official permissible PM2.5 limit is 60 gm-3, while that of PM10 level is 100 gm-3.

A 'severe' air quality index (AQI) essentially means that even healthy people may suffer from respiratory illnesses on a prolonged exposure to such air. This air will seriously affect those with ailments, according to the advisory issued by SAFAR.

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".

AQI above 500 falls in the "severe-plus emergency" category.

AQI is the combined impact of different pollutants, including PM (particulate matter) 10, PM 2.5, nitrogen and sulphur oxides and ozone.

Delhi's air quality on Thursday went off the charts to the "severe plus emergency" category as smog caused due to smoke from firecrackers engulfed the national capital.

The overall AQI Thursday was recorded in the "severe plus emergency" category at 642, according to data from SAFAR.

The spike in pollution levels on Thursday was caused by rampant burning of firecrackers that had led to the formation of a smoky layer across the national capital and drastically reduced visibility, authorities said.