Delhi’s pollution level remained ‘severe’ for the second day as a thick haze engulfed the national capital, even as authorities said there was significant improvement in the air quality compared to Thursday.

According to data by the Central Pollution Control Board, the overall air quality index (AQI) was recorded at 426 which falls in the ‘severe’ category. The System of Air Quality and Weather Forecasting And Research (SAFAR) said the city’s air quality has “improved significantly” since Thursday, but the recovery was slow due to low surface wind speed.

“At present, it continued to be in ‘severe’ but likely to improve further and will become ‘very poor’ by afternoon and will improve further by Saturday. The contribution of PM2.5 in PM10, which was 75 per cent on Thursday (against normal 55 per cent), has been reducing,” SAFAR said.

It also said contribution to the PM2.5 pollution due to stubble emission was marginal. According to CPCB data, about 28 areas in Delhi recorded ‘severe’ air quality, while four areas recorded ‘very poor’ air quality. On Friday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded at 272 µgm-3.

According to SAFAR, the PM10 (particles in the air with a diameter of less than 10 micrometres) level was recorded six times the permissable limit at 422 µgm-3. 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.

Delhi’s air quality on Thursday went off the charts to ‘severe plus’ emergency category as smog caused due to smoke from firecrackers engulfed the national capital. The overall AQI was recorded in the “severe plus emergency” category at 642, according to SAFAR data.

The sharp spike in pollution 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 the visibility, the authorities said.

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