Delhi's air quality deteriorated on Tuesday with seven areas in the national capital recording severe pollution levels, and authorities said the situation is likely to worsen over the next two days.

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The Central Pollution Control Board recorded an overall air quality index (AQI) of 355, which falls in the "very poor" category.

Six areas Ashok Vihar, Anand Vihar, Burari, Mundaka, Mathura Road, Punjabi Bagh and Wazirpur recorded severe air quality, according to CPCB.

Twenty six areas of Delhi recorded very poor air quality, while in four areas it was in the "poor" category, CPCB data showed.

An AQI between 201 and 300 is considered poor, 301 and 400 very poor and 401 and 500 is severe.

The PM2.5 (fine particulate matter in the air with a diameter of less than 2.5 micrometre) level was recorded at 208 and the PM10 level at 397, it said.

Ghaziabad recorded severe pollution level at 404 while Faridabad and Noida experienced very poor air quality.

In Gurgaon, the air quality was poor, the data showed.

The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the AQI dropped speedily as expected, but remained very poor.

"Although increasing AQI trend is predicted from tonight for next two days, it will remain in 'very poor' range only. This is mainly due to a decline in wind speed along with adverse meteorological conditions. The contribution from long-range dust or stubble biomass is negligible," SAFAR said.

According to the Indian Institute of Tropical Meteorology, the maximum ventilation index was likely around 3,500 sqm/second on Tuesday.

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

Delhi's air quality has largely remained in the "very poor" category for a week. It had improved to "poor" category for a brief period on Saturday but again slipped to "very poor" on Sunday, authorities said.