New Delhi, Oct 29 (IANS): Following Diwali, the air quality index (AQI) in the national capital on Tuesday morning was in the "very unhealthy" category, although it had crossed the hazardous category during early morning.

As per data from the US Embassy here, the PM 2.5 count on Tuesday morning stood at 297. There was a spike at 3 a.m. which took the AQI to hazardous levels of over 300. The spike lasted from 3 a.m. to 7 a.m.

The highest count registered was 306 at 3 a.m. The hazardous category causes serious aggravation of heart or lung diseases and premature mortality in persons with cardiopulmonary disease and among the elderly and poses serious risk of respiratory effects in the general population.

According to a forecast by Safar India, biomass related contribution may touch this year's peak value of 25 per cent) on Tuesday. AQI is forecast to improve to the higher-end very poor category, and a slight increase in wind speed by Wednesday is expected to help improve AQI marginally to middle-end of the very poor category.

The unfavourable factors for AQI are increasing biomass fire counts, the stubble transport level wind in a northwesterly direction, and incidents of burning firecrackers. Haryana and Punjab stubble fire counts are increasing, and the transport level wind direction is favourable for plume transport.