A thick grey haze swallowed the skyline, reduced visibility on roads and brought back irritation in the eyes and throat as Delhi woke up to alarmingly high pollution levels on Monday, after firecrackers were burst across the city well past the permitted hours on Diwali. A thick blanket of smog engulfed several parts of the National Capital on Monday morning, a day after Diwali celebrations, with air quality deteriorating to the ‘severe’.