New Delhi, Nov 12 (IANS): The air quality of Delhi and regions around it remained toxic between "severe" and "very-poor" levels even five days after Diwali, with weather conditions expected to be unfavourable till at least November 15.

The Air Quality Index (AQI) of Delhi was 399 at 4 p.m. considered "very-poor", which by 6 pm worsened to 404 considered "severe".

On Monday, the national capital saw variable winds with dry and cold north-westerly in the noon which improved the air quality. However by the evening, winds changed into moist easterly.

According to weather analysts, the weather conditions are expected to remain same till November 15.

With persistent threats of adverse health effects since Diwali, the System of Air Quality and Weather Forecasting And Research (SAFAR) on Monday cautioned people again against doing strenuous outdoor physical activities.

"If asthmatic, keep relief medicine handy... Stop outdoor activity early morning and after sunset. Go for a short walk instead of a jog and take more breaks. Stop any activity level if you experience any unusual coughing, chest discomfort, wheezing, breathing difficulty, or fatigue," SAFAR warned.

On Monday, apart from Gurugram (AQI 191 or moderate), all other regions in NCR suffered a severe air quality with AQI 411 in Noida, 423 in Ghaziabad, 401 in Greater Noida and 454 in Faridabad, on a scale of 0 to 500.

The major pollutant PM2.5 or particles with diameter less than 2.5mm, were well above severe levels across Delhi-NCR.

At 6 pm, the average aggregation of PM2.5 across 36 stations was 271 microgrammes per cubic meters, while the same acorss 49 areas of NCR was 265 units.

Chandni Chawk, Pitampura, Delhi University, Dhirpur and Mathura Road, among other, were the most polluted regions with PM2.5 well above 430 units by the evening.

The safe limit for PM2.5 is 60 units as per national standards and 25 units according to the international standards.

"Both PM2.5 and 10 get into the lungs and cause cardiovascular and respiratory diseases, but PM2.5 is more dangerous because it mixes with blood stream," Shambhavi Shukla, Senior research associate with the Centre for Science and Environment (CSE), told IANS.

She said some international studies have noted that particle pollutants have a direct effect on life expectancy.