The raster files available for download here are modeled based on daily global measures of CO2 concentration available from NASA JPL's Orbiting Carbon Observatory-2 (OCO2; see figure 1 for an example of coverage). CO2 concentration is defined as the average concentration of carbon dioxide in a column of dry air extending from Earth’s surface to the top of the atmosphere. The daily measures from OCO2 are concatenated for an entire year and then aggregated to a regular global 10km grid. Points flagged in the OCO2 data as lower quality are omitted. The resulting grid is then interpolated using linear interpolation to fill gaps, and produce a final yearly raster surface. Units of the raster are the CO2 concentration in parts per million (ppm).
The underlying data were produced by the OCO-2 project at the Jet Propulsion Laboratory, California Institute of Technology, and obtained from the OCO-2 data archive maintained at the NASA Goddard Earth Science Data and Information Services Center.