Using a Lidar, a laser ranging instrument, at the University’s Bayfordbury Observatory near Hertford, the team monitored the height of the particles throughout the day. Laser pulses reflected from the particles show their arrival around midday, their growing height in the atmosphere, and their eventual departure in the evening.The atmospheric profile was measured every second, allowing the changes in the particle layering to be observed throughout the day. The particles responsible for the red sky are seen as a diagonal stripe in the profile sequence. The layer of dust arrived over Hertford around 11:00 GMT at 1 km altitude, drifted past over the next 6 hours at progressively higher altitudes, and reached 2-3 km altitude by the time it moved away from Hertford around 18:00 UTC.