Total ozone column retrievals from DSCOVR/EPIC compared to data from the Pandonia Global Network

Total ozone column (TO3) is one of the output products of the Earth Polychromatic Imaging Camera (EPIC), which has been observing the Earth on board the Deep Space Climate Observatory (DSCOVR) since 2015. From its unique Lagrange 1 observation point, EPIC obtains TO3 for the entire sunlit portion of our planet and therefore retrieves TO3 over a given ground location from sunrise to sunset every 65 min in the Northern Hemisphere summer and 110 min in winter. This is a much higher temporal resolution than possible for Low Earth Orbit (LEO) satellites that typically retrieve TO3 over a given ground location once per day around local noon. Therefore, when comparing time-varying TO3 from EPIC and LEO-satellites, one is limited to a rather small subset of EPIC data. As a consequence, in order to validate EPIC TO3, it is also necessary to compare them to ground-based measurements, where the full daily TO3 cycle can be covered. With currently more than 70 operational locations worldwide, the Pandonia Global Network (PGN) has officially been producing column amounts of several trace gases, including ozone, since 2018, with data records that date back as long as into 2012. The new version 1.8 PGN TO3 product has several improvements compared to previous versions, most prominently a better treatment of the effective ozone temperature and a more elaborate stray light correction for those instruments that have undergone a stray-light calibration in the laboratory. In this work we compare TO3 data from EPIC and PGN for selected ground locations with an emphasis on the influence of the solar zenith angle and the effective ozone temperature on the data.