Delhi's air quality slips to poor category as impact of rainfall subsides: authorities

Delhi's air quality slipped into poor category as the impact of rainfall in cleansing the air subsided, with authorities predicting further deterioration in the next two days.

The city's air quality index (AQI) dropped to 247, which falls in the 'poor' category.

The national capital recorded its best air quality in moderate category in over two months on Thursday after rains washed away pollutants.

Three areas -- Jahangirpuri, Wazirpur and CRRI Mathura Road -- recorded very poor air quality while 25 areas recorded poor air quality and four recorded moderate air quality, the Central Pollution Control Board said.

According to the Centre-run System of Air Quality and Weather Forecasting (SAFAR), the air quality would deteriorate further to very poor category by Saturday as the impact of rainfall has subsided and all other meteorological conditions are "adverse".

The overall PM2.5 (fine particulate matter in the air with a diameter of less than 2.5 micrometre) level was recorded at 116 and the PM10 (fine particulate matter in the air with a diameter of less than 10 micrometre) level at 196, it said.

An AQI between 100 to 200 comes under moderate category, 201 and 300 is considered 'poor', 301 and 400 'very poor' and 401 and 500 'severe'.

Neighbouring Ghaziabad, Noida and Faridabad recorded 'poor' air quality, while Gurgaon recorded 'moderate' air quality, the CPCB data showed.

According to the Indian Institute of Tropical Meteorology, the maximum ventilation index is 6,500 sqm/second on Friday.

A ventilation index lower than 6,000 sqm/second with average wind speed less than 10 kmph are unfavourable for dispersion of pollutants.