New Delhi, Dec 5 : A day after the air quality of the national capital slipped into the "severe" category, the quality index slightly improved to "very poor" category on Monday. According to the System of Air Quality and Weather Forecasting And Research (SAFAR), the city's overall Air Quality Index (AQI) was recorded at 340 in the "very poor" category this morning. The concentration of both PM 2.5 and PM 10 in the environment was recorded at 340 and 204 respectively under "very poor" and "poor category" respectively. As per the SAFAR forecast, the city's air quality will continue in "very poor" category with AQI escalating to 327 on Tuesday. Notably, 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". Meanwhile, to prevent further deterioration of the air quality, the Sub-Committee for operationalisation of the revised GRAP on Sunday invoked the Stage III of the GRAP with immediate effect in the Delhi-NCR area, in addition to all action under Stage I and Stage II of the GRAP. The air quality index at Pusa, Lodhi Road, and Mathura Road were recorded 346, 309 and 341 respectively in the very poor category this morning as per the SAFAR system. The prolonged exposure to "poor" category air quality may lead to respiratory illness. However, the overall Air Quality Index of Delhi's neighbouring cities of Noida further deteriorated into the "very poor" category with the air quality index recorded at 375. Gurugram's overall air quality has also further deteriorated to the "very poor" category as the AQI was reported at 326. /IANS