Development of an inversion system for biogenic isoprene emissions in IFS-COMPO

We report on the development of an inversion system for biogenic emissions within ECMWF’s Integrated Forecasting System IFS-COMPO.  As part of the Horizon Europe CAMEO (CAMS EvOlution) project, a satellite-retrieval based inversion system for surface fluxes of biogenic volatile organic compounds was implemented in the IFS global model. The scheme is based on formaldehyde (HCHO) satellite observations from multiple satellite instruments. As part of the work, an assimilation capacity for formaldehyde was developed for use in IFS-COMPO, which uses the 4DVAR data assimilation technique. The extension for HCHO assimilation applies the tangent linear and adjoint of recently developed simplified formaldehyde-isoprene chemistry scheme. The purpose of the adjoint simplified chemistry scheme is to enable a modification of the isoprene fields based on the assimilation of HCHO observations. The impact of the assimilation of HCHO in IFS-COMPO is analyzed using TROPOMI S5P formaldehyde observations, with a particular focus on its impact on HCHO as well as key atmospheric reactive trace gases, such as isoprene, ozone, and carbon monoxide. We further present first optimizations of the a priori biogenic isoprene emissions based on HCHO satellite observations. Particular focus is put on the sensitivity of the implemented simplified HCHO chemistry to isoprene emissions by systematically investigating the link of isoprene and formaldehyde both in the IFS standard configuration and when using the new simplified HCHO chemistry scheme. The latter is assessed by scaling climatological a-priori isoprene emissions by differing factors and consecutively analysing the resulting variance of full-IFS-COMPO and simplified-chemistry formaldehyde in respective IFS-COMPO forecasts.