Delhi's overall Air Quality Index (AQI) is on the verge of becoming "severe" after it deteriorated to 398 on Tuesday, according to official data.

The System of Air Quality and Weather Forecasting And Research (SAFAR) said that with the air quality dipping in the national capital, there is an increase in carbon monoxide (CO) levels in some areas, posing a threat to children and senior citizens.

The PM 2.5 and PM 10 concentration stood at 398 and 392, respectively, both under the same "very poor" category, according to the SAFAR data.

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".

The AQI in Noida stood at 462 under the "severe" category, while in Gurugram it was 398 under the "very poor" category.

The "severe" category calls for health warnings of emergency condition and even posed serious respiratory risks to the general public.

In Anand Vihar, Pusa and Mathura Road, the AQI stood at 449, 408 and 421, respectively, all under the "severe" category.

In Lodhi Road, the air quality was recorded at 369 or "very poor".

According to the forecast from SAFAR, the air quality of the national capital will deteriorate further on Wednesday.