The air quality index in Delhi on Tuesday morning remained under "severe" category at 506 level, according to System of Air Quality Forecasting and Research (SAFAR). Delhi's adjoining areas like Noida and Gurugram saw the air quality at ''severe" level with PM 2.5 at 674 mark and "very poor category" at 383 mark, respectively.
In Delhi, the North campus area saw the worst air quality index at 7:45 am today when PM 2.5 stood at 740. In IIT Delhi, the AQI was at 460 mark, which falls under "severe" category.
An AQI between 0 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".
An advisory was issued by SAFAR -- Air Quality Forecasting system SAFAR for Metro cities -- asking people to avoid outdoor physical activity. People with heart and respiratory diseases were asked to remain indoors.
Authorities have blamed spike in post-harvest stubble burning rather than Diwali effect for Delhi's air quality. In fact, Delhi Chief Minister Arvind Kejriwal on Monday said the post-Diwali pollution level in the national capital was the lowest in five years.
The air quality in Delhi after Diwali this year was worst than 2015, 2016 and 2017. Last year, the air quality index, as per SAFAR, was noted at 642. In 2015, 2016 and 2017, the AQI on the next day of Diwali was 360, 445 and 367.
Health experts say that being exposed to such noxious air for long can cause serious damage to lungs, risks of pneumonia, extreme bronchitis and other respiratory diseases.