The ozone loss at 12:00 GMT of each day from GOME (1996-2002) and SCIAMACHY (2003-2006) Assimilated Ozone Fields. The ozone loss is the amount of ozone in megaton necessary to fill the ozone hole to 220 Dobson units (DU) over the whole area. DU stands for the total thickness of ozone in a given vertical column if it were concentrated into a single slab at standard temperature and atmospheric pressure – 400 DUs is equivalent to a thickness of four millimetres, for example.