New Delhi, Jan 19 : The national capital on Friday recorded a minimum temperature at 7.1 degrees Celsius, one notch below the seasonal average, the India Meteorological Department said. The IMD's forecast showed that the maximum temperature on Friday is likely to hover around 18 degrees Celisus. Several flights operations were also reported to be delayed owing to low visibility. 'Visibility at Palam Airport (Delhi) improved from 00 m at 0430 IST to 50 m at 0500 IST and further improved to 150 m at 0630 IST and it is still continuing at 150 m,' the IMD said in tweet around 7 a.m. However, at 8:30 a.m. the visibility improved and 500 metres visibility was recorded at Palam and 400 m at Safdarjung. Moreover, the air quality continued to remain in the 'very poor' category at several stations across the city. In the Anand Vihar area, at 9 a.m., PM2.5 levels were recorded to be in the 'very poor' category standing at 348 and PM10 reached 242 or 'poor', according to the Central Pollution Control Board (CPCB). The Air Quality Index (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 IGI Airport T3 witnessed PM2.5 levels at 210 or 'poor', and PM10 was at 135, falling under the 'moderate' category. /IANS