New Delhi, Nov 7 : The air quality in Delhi on Tuesday morning again dipped to 'severe' category after improving very slightly. On Monday evening, the air quality in Delhi-NCR improved slightly with an overall Air Quality Index (AQI) at 399, in the 'very poor' category, according to data from the System of Air Quality and Weather Forecasting And Research (SAFAR). However, on Tuesday the quality again fell into the 'severe' category. In the national capital, the Anand Vihar station remained in the 'severe' category with PM 10 at 500 and PM 2.5 also reached500 while the CO was at 112 and NO2 at 123, both under 'moderate' category, as per the Central Pollution Control Board (CPCB). The AQI between zero 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'. At Delhi Technical University (DTU) station, the PM 2.5 reached 315 under 'very poor' category while PM 10 was at 411 under 'severe' category. The CO was recorded at 103, under the 'moderate' category. The station at Dwarka sector 8 recorded PM 10 at 486 and PM 2.5 at 493 ('severe'), while CO was at 119 and NO2 was at 132, both under moderate category. However, at Dwarka sector-8 station the PM 2.5 was at 459 and PM 10 was at 457, both under severe category . The NO2 levels reached 113 and CO at 118, both under moderate category. The air quality at the Indira Gandhi International (IGI) Airport T3 area was in the 'severe' category with PM 2.5 at 441 and PM 10 at 402 while the CO reached 58 in the 'satisfactory' category. The PM 2.5 at ITO was recorded at 401, putting it in the 'severe' category while PM 10 reached 256, placing it under 'poor' category. The Nitrogen Dioxide (NO2) was recorded at 168 ('moderate') on Tuesday morning. At Lodhi Road, the AQI with PM 2.5 concentration was at 383 under the 'very poor' category, while PM (particulate matter) 10 was recorded at 357, also in the 'very poor' category while CO (Carbon Monoxide) was at 129 in moderate category. /IANS