An online parameterization of biogenic VOC emission fluxes in the Integrated Forecasting System for atmospheric composition

 

Biogenic volatile organic compounds (BVOCs) are important contributors to atmospheric chemistry and act as precursors of secondary organic aerosol, formaldehyde (HCHO) and carbon monoxide. In presence of high NOx the emitted isoprene may also contribute significantly to the production of tropospheric ozone. As such, having a good handle on BVOC emissions is important for global air quality analyses and forecasts, as produced operationally as part of the Copernicus Atmosphere Monitoring Service (CAMS). Currently, analyses and forecasts as generated using ECMWF’s Integrated Forecasting System for atmospheric composition (IFS-COMPO), use offline monthly datasets for biogenic emissions based on CAMS-GLOB-BIO. However, this approach lacks the ability to capture the daily variability in biogenic VOC emissions, while also the near-real time forecasts have to rely on climatological emissions.

This has motivated the implementation of an online parameterization for the description of BVOC emissions based on the MEGAN scheme, as part of the ECLand module. Having the BVOC emissions as an integral part of the IFS allows the use of the latest parameterization of soil and vegetation properties, together with accurate description of meteorological quantities, which are both important drivers with respect to biogenic emissions. Also, the resulting emissions can be directly used in the atmospheric chemistry module, which has recently been updated with respect to isoprene chemistry. This also enables an indirect evaluation of the emissions using TROPOMI observations of HCHO.

In this contribution we present the current status of the implementation of the online biogenic VOC emissions module into the IFS and provide a first assessment by comparing these emissions to a reference CAMS-GLOB-BIO dataset. Also we evaluate the resulting isoprene emissions in terms of HCHO columns using TROPOMI retrievals, along with its impact on surface ozone and secondary organic aerosol. We highlight uncertainties in different aspects along the parameterization and evaluation chain.