New Delhi, Oct 27 (IANS): The air quality index (AQI) breached the 400-mark in the national capital on Thursday with Anand Vihar recording an AQI of 428, followed by Ashok Vihar at 405, both in the 'severe' category, according to Central Pollution Control Board (CPCB) data.

With Delhi's overall air quality remaining in the 'very poor' category, experts said the toxic gas can cause severe reactive airway dysfunction (RADS) even in absolutely healthy people.

The air quality in the national capital deteriorated to 'very poor' category due to calm winds and cool weather conditions, weathermen said.

According to data from the System of Air Quality and Weather Forecasting and Research (SAFAR), the concentration of (particulate matter) PM 10 and PM 2.5 was recorded at 219 and 316 in Delhi, respectively.

The AQI was 329 in PUSA, 310 at Lodhi Road, and 347 at Mathura Road.

The AQI in Noida, Greater Noida, Ghaziabad and Gurugram stood at 354, 368, 373 and 362, respectively, all under the 'very poor' category.

An AQI between zero 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'.

According to SAFAR forecast, Delhi's air quality will continue to remain under the 'very poor' category until Saturday.

According to environmentalist ChandarVeer Singh, humidity is expected to rise in the coming days as wind flow slows down, trapping particulate matter in cool weather conditions.

"The pollution levels will rise till December and every resident should be cautious and stay indoors. We as responsible citizens should also use public transport and avoid personal vehicles and contribute to reducing fumes released from vehicles. It is time for the government to take strict steps and control the rising pollution levels," he said.