The European Space Agency (ESA) Precursors for Aerosols and Ozone Climate Change Initiative (Precursors CCI) project is part of ESA's Climate Change Initiative (CCI) to produce long term datasets of Essential Climate Variables derived from global satellite data.

This project is developing long-term climate data records of the GCOS Precursors for Aerosol and Ozone Essential Climate Variable. Precursors include the short-lived atmospheric trace gases: nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO), formaldehyde (HCHO), and ammonia (NH3).

Working in close liaison with climate data users, the project focuses on building consistent/harmonised long term multi-satellite mission climate data records from satellite instruments including GOME, SCIAMACHY, GOME-2, OMI, TROPOMI, IASI, and MOPITT.

The resulting datasets will include both single sensor level-2 and level-3 gridded products but also unique multi-sensor merged data series covering, for some variables, almost 3 decades of observations. These products will be fully documented according to CCI standards, and generated in a common data format following the netCDF CF metadata conventions.