The Earth Polychromatic Imaging Camera (EPIC) on the DSCOVR spacecraft provides measurements of Earth-reflected radiances from the entire sunlit portion of the Earth. The measurements from four EPIC UV channels are used to reconstruct global distributions of total ozone. The tropospheric ozone columns (TCO) are then derived by subtracting independently measured stratospheric ozone columns from the EPIC total ozone.

TCO data product files report gridded synoptic maps of TCO measured over the sunlit portion of the Earth disk on a 1-2 hour basis. Sampling times for these hourly TCO data files are the same as for the EPIC L2 total ozone product. This Version 1.0 of the TCO product is based on Version 3 of the EPIC L1 product and the Version 3 Total Ozone Column Product. The stratospheric columns were derived from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) ozone fields (Gelaro et al., 2017). In contrast to the EPIC total ozone maps that are reported at high spatial resolution of 18 × 18 km2 near the center of the image, the TCO maps are spatially averaged over several EPIC pixels and reported on a regular spatial grid (0.25° latitude × 0.25° longitude).

Kramarova et al. (2021) provides a detailed description of the EPIC TCO product and its evaluation against independent ozonesondes and satellite measurements.  Table 1 in Kramarova et al. (2021) lists all of the variables included in the TCO product files.  Ozone arrays in the product files are integrated vertical columns in Dobson Units (DU; 1 DU = 2.687×10^20 molecules/m^2).