The OMI detector suffers from the so-called row anomaly which reduces the amount of usable pixels. The pixels affected by the row anomaly are flagged in the data and this can be seen as a north-south gap in the images. More detailed information about the row anomaly can be found here.

The East-West gap on easterly overpasses is caused by the data dumping from the satellite memory to the ground station at Svalbard. Direct Broadcast used by the OMI VFD processing is disabled during this memory dumping. For westerly overpasses, a different ground station is used. Therefore, no such gaps exists in these data.