The air quality of the national capital improved significantly from 'severe' to 'very poor' category on Tuesday.

Delhi's overall Air Quality Index (AQI) crossed 300 on Tuesday morning which falls in the 'very poor' category, as against 440 on Monday.

An AQI between 0-50 is considered 'good', 51-100 is 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 as 'severe'. An AQI above 500 falls in the 'severe plus' category.

Air quality levels further deteriorated in Anand Vihar, recording pollution levels at 412, making it fall in 'severe' category. In Ghaziabad, air quality index was 348, and in Noida it was 427.

According to System of Air Quality and Weather Forecasting and Research (SAFAR), "A fresh water disturbance is very likely to affect the region by December 31 and improve surface wind speeds and ventilation. Improvement in AQI towards higher end or the 'very poor' category is expected. Further improvement, to the middle of the 'very poor' category, is expected by January 1, 2020".

They further advised everyone to reduce heavy exertion. People with heart or lung disease, adults and children should avoid longer or heavy exertion.

The AQI of Delhi had touched 494 in November this year, making it the highest level since it touched 497 in November 2016. In comparison, the highest AQI recorded in 2018 was 450 in December.