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). These gases are emitted to the atmosphere by many different anthropogenic and natural processes and cause the formation of secondary aerosols and tropospheric ozone, which are harmful to animal and plant life, perturb the Earth's radiative balance, and affect the lifetimes of other climatically important atmospheric constituents.

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.

The final climate data research of ozone and aerosol precursors that will be delivered to users, will provide an unprecedented data set of observations documenting the variability and long-term changes of the tropospheric composition. Observations of precursor gases are needed to develop emission-based scenarios for radiative forcing by tropospheric ozone and secondary aerosols, due to both anthropogenic and natural sources. They are also useful as such to study changes in air quality and their relationship with climate changes. Users span from scientists studying atmospheric composition changes and related processes, to climate modellers and environmental services, in particular the Copernicus Atmospheric Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S). Within the project, three specific use case studies will be developed by our climate research group to assess the usability and fitness for purpose of the generated data series, addressing respectively the impact of precursors data product on CAMS reanalysis, and their use to assess global and regional modelling studies of the tropospheric composition.


Trends in HCHO columns between 2005 and 2015 observed by OMI (left) and simulated with a global model (right). The positive trends seen at high latitudes are due to the warming climate and are well reproduced by the model. The OMI data reveal clear evidence that HCHO observations reflect climate variability and its trends (Stavrakou et al., 2018). Long-term HCHO data such as shown here underline the usefulness of long-term data records, as the 5 that are planned to be developed within this proposal.