The OCO-2 Carbon Dioxide (Total Column Average) layer displays the column-averaged dry-air mole fraction of carbon dioxide (XCO₂) in the vertical column of the atmosphere (i.e. from Earth’s surface to the top of the atmosphere) and is measured in parts per million (ppm).

Carbon dioxide (CO₂) is an odorless, colorless gas and is the fourth most abundant component of dry air (after nitrogen, oxygen and argon). CO₂ is an important greenhouse gas that helps trap heat in the atmosphere. As a part of the carbon cycle, CO₂ can be emitted (e.g. from respiration by plants and soils or from wildfires) or absorbed (e.g. from plant photosynthesis or by dissolving into the oceans). Human activities such as the combustion of fossil fuels and biomass burning are sources of CO₂.

The Orbiting Carbon Observatory-2 (OCO-2) is a three-channel imaging grating spectrometer that collects cloud-free XCO₂ observations continuously over the globe by measuring reflected sunlight in the near-infrared. The OCO-2 Carbon Dioxide parameter is taken from the OCO-2 Level 2 Lite product. OCO-2 makes eight simultaneous, adjacent measurements, each with a spatial resolution of 2.25 km x 1.29 km. These measurements are then mapped onto a 500 m² grid. The repeat cycle for OCO-2 is every 16 days.

References: Crisp et al. The ACOS CO2 Retrieval Algorithm - Part 2: Global XCO2 data Characterization Atmos. Meas. Tech., 5, 687-707, 2012; GES DISC - OCO-2 Documents; OCO-2 Data Center