New Delhi: The air quality in the National Capital Region (NCR) has deteriorated to 'severe' levels yet again this season, engulfing the region in a toxic smog.

The Air Quality Index (AQI) rose to '467' in Delhi on Wednesday, according to System for Air Quality and Weather Forecasting and Research (SAFAR). AQI above 400 falls in the 'severe' category, and experts advise even healthy people to limit their exposure to toxic air as there could be respiratory risks.

Noida was the worst hit with the AQI rising to the 'severe+' levels of 572, followed by Gurugram at '511'.

The situation had improved last week after scattered showers settled pollutants, bringing down the AQI to 'very poor' to 'poor' levels across major parts of the region.

As per the latest forecast, the air quality is not likely to improve over the next two days as conditions favour transport of biomass plume from stubble burning across north-western states to Delhi. Since the wind speed is low, pollutants are expected to remain arrested in the stagnant air, creating breathing difficulties for people. As per SAFAR, the contribution of fire counts to Capital's pollution could be anywhere around 22% on Wednesday.

No respite is expected till Friday morning, when a western disturbance approaching the upper Himalayan region, could provide some push to the winds. Though there is low likelihood of any rain in Delhi, the sky would remain partly cloudy for the next two days.

"The mixing depth (level at which pollutants mix with the air) and ventilation coefficient is showing a decrease trend over the next two days and AQI might just enter 'Severe+' category in some parts of the Capital," as per SAFAR.

While winter has already set in, the weather department predicts no major change in overall temperature across NCR/Delhi. A rise in minimum temperature is though expected over the next two days by at least 2-3°C over north-west India.