New Delhi, Nov 27 : Delhi was enveloped with a layer of smog on Sunday morning and the air quality index (AQI) in the national capital continued to be in "very poor category" at 315. According to the System of Air Quality and Weather Forecasting And Research (SAFAR), the concentration of both PM 2.5 and PM 10 in the environment was recorded at 315 and 210 under "very poor" and "poor category" respectively. As per the SAFAR forecast, the city's air quality will further deteriorate with AQI escalating to 326 in the "very poor category" on Monday. 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". However, the AQI of Delhi's neighbouring cities of NOIDA also remained into the "very poor category" at 345 with PM 2.5 concentration at 345 and the PM 10 concentration at 207 under "very poor" and "poor category" respectively. While Gurugram's overall air quality also deteriorated further to the "very poor category" with AQI at 319. The PM 2.5 concentration was recorded at 319 and the PM 10 concentration at 191, both under "very poor" and "moderate category". /IANS