Delhi's pollution level began to rise again on Wednesday as the impact of rain subsided, causing the air quality index (AQI) to slip into the 'poor' category, authorities said.

According to the Central Pollution Control Board (CPCB) data, the overall AQI in the city was 218.

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

On Tuesday, Delhi recorded its lowest pollution levels since October last year as heavy rains lashed the city and the wind speed picked up. The national capital's air quality was recorded in the 'satisfactory' category.

On Wednesday, 27 areas in Delhi recorded 'poor' air quality while it was 'moderate' in three areas, the CPCB said.

In the National Capital Region, Noida, Faridabad, Ghaziabad, Gurgaon and Greater Noida recorded "poor" air quality, it said.

The overall PM2.5 level —fine particulate matters in the air with a diameter of less than 2.5 micrometers -- in Delhi was 101, while the PM10 level was 154, it said.

But as the impact of rains subsided, the pollution level again started to rise. It is expected to oscillate between 'moderate' and 'poor' categories for the next three days, authorities said.

The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality is likely to deteriorate now.

"It is likely to go to lower level of 'very poor' for next two days. Moderate foggy conditions due to radiation fog will prevail for the next two days over Delhi and surrounding regions," the SAFAR said.