New Delhi, Jan 07 (ANI): Delhiites woke up to yet another cold and foggy morning on Sunday. Air Quality Index of Delhi's Lodhi Road area shows prominent pollutant PM 2.5 remains in ' very poor' category. Air pollutant PM2.5 is fine particulate matter which is a concern for health when levels in air are elevated. The tiny particles of PM2.5 reduce visibility and cause the air to appear hazy when levels are high. Fog continued to affect rail traffic in the national capital with as many as 128 trains being cancelled. At least 36 trains were delayed and 9 rescheduled as low visibility continues to hamper rail operations.