New Delhi, Jan 11 : The national capital woke up to a minimum temperature of 5.8 degrees Celsius, which is the seasonal average, according to India Meteorological Department (IMD). It added that the maximum temperature is likely to hover around 15 degrees, making Thursday a cold day. The city, on Thursday morning, was blanketed by dense fog with lowest visibility of 500 m at Safdarjung at 8:30 a.m. while the Palam recorded 100 m at 5:00 a.m., which improved later. The IMD classifies fog intensity into four types: shallow, moderate, dense and very dense fog. The visibility ranges from 999 m to 500 m, 499 m to 200 m, 199 m to 50 m and less than 50 m, respectively. According to Indian Railways, 24 trains were running late by hours due to fog and cold wave. The Air quality continued to remain in the 'very poor' category at several stations across the city. At the Anand Vihar area, PM2.5 levels remained into the 'very poor' category standing at 355 and PM10 reached 253 or 'poor'. 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 Dwarka Sector 8 also witnessed PM2.5 levels at 332, the 'very poor' category while the PM10 was at 222, falling under the 'poor' category, again. /IANS