Slow wind speed and high humidity brought the air quality of Delhi to 'very poor' category on Sunday, authorities said. The overall air quality index (AQI) was recorded at 326, which comes under 'very poor' category, the Centre-run System of Air Quality and Weather Forecasting (SAFAR) said.
The air quality in the national capital is very poor and is expected to remain in the same category with gradual increase for the next three days as wind speed is slow and humidity is high, it said.
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According to the data by Central Pollution Control Board (CPCB), 20 areas in Delhi recorded 'very poor' air quality while 13 recorded 'poor' air quality.
On Sunday, the PM2.5 — particles in the air with a diameter of less than 2.5 micrometres — level was recorded at 163, while the PM10 level was recorded at 306, the CPCB data showed.
Ghaziabad, Faridabad, Noida and Greater Noida recorded 'poor' air quality while Gurgaon recorded moderate air quality, the data said.
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'.
"Fire counts from stubble burning declined significantly and hence have negligible impact," it said.
Significant improvement was seen in the air quality of Delhi on Wednesday and Thursday after pollutants were washed away by rain, the SAFAR said.
The rainfall however, also led to increased air capacity to hold pollutants, it said.