Spectral Reference Data for Atmospheric Monitoring

This project addressed the need to improve the quality of the reference spectral line data used in a wide range of spectroscopic methods that determine concentrations of greenhouse gases and pollutants in the atmosphere for climate studies and environmental monitoring. The quality of spectroscopic data depends on the accuracy of the underlying molecular spectral line data. As data is needed throughout the atmosphere, a particular challenge is understanding how the properties of the molecules to be measured vary with temperature, pressure and atmospheric composition. With the large number of existing and planned global atmospheric monitoring networks and satellites dedicated to environmental monitoring, there is a global need for a long-term infrastructure to provide high quality spectral data.

The project established a coordinated European measurement infrastructure for traceable spectral reference data to support accurate atmospheric measurement data, through:

• A central spectroscopic facility (CF) based on a modified high-resolution visible to mid-infrared Fourier-transform spectrometer was developed. It determines accurate spectral line data for key molecular species including their dependence on temperature from 200 K to 350 K and pressure from 0.01 mbar to 1000 mbar, covering the relevant conditions for tropospheric and stratospheric studies. The facility is validated via high-resolution laser-based facilities at NMIs across Europe and accurate gravimetric dilution gas reference standards and full uncertainty assessments. It has an open interface structure allowing access by the climate science community.
• Traceable spectral line data for a range of greenhouse gas species with metadata including traceability statements and uncertainty flags for key greenhouse gases: carbon dioxide, methane and nitrous oxide. This data will be included in the forthcoming revision of the widely used database of spectroscopic data HITRAN, increasing the amount of SI traceable data in the database.

The ongoing activities to produce accurate spectral line data will improve atmospheric measurements based on spectrometric methods, providing more reliable data for environmental monitoring and modelling. A key user of the HITRAN database, for example, is the Total Carbon Column Observing Network, made up of 23 ground-based atmospheric monitoring stations distributed across the globe that also validate satellite measurements. The improved data will help to remove discrepancies between satellite and surface measurements.