Initial steps towards an inversion system for biogenic isoprene emissions in CAMS: Verification using HALO mini-DOAS and TROPOMI observations and simplified chemistry

We report on an extensive analysis of CAMS (Copernicus Atmospheric Monitoring Service) formaldehyde (HCHO) simulations in different tropospheric regions, seasons, altitudes and air masses using a comprehensive data set of airborne measured HCHO vertical column densities and mixing ratios. The observations are derived from measurements of the HALO mini-DOAS instrument operated from aboard the German research aircraft DLR HALO during six international research missions in the years 2017 to 2019. In addition, measurements over the South American tropical rain forest in 2014 are included, as this region is of particular interest in the analysis of global biogenic emissions. The analysis of airborne measured and CAMS CY48R1 simulated HCHO vertical profiles shows an overestimation of planetary boundary layer HCHO over the Amazon rain forest by the model on average by 70%. Restricting the comparison to measurements outside of identified anthropogenic emission events (e.g. biomass burning plumes) increases this overestimation of boundary layer HCHO to a factor of five. This finding is further investigated by additionally also including vertical column density measurements of the mini-DOAS instrument to the analysis. This allows the comparison of simulated and airborne derived HCHO with respective TROPOMI satellite observations (for all airborne measurements from May 2018 onwards), hence enabling a comprehensive assessment of tropospheric HCHO. The above findings are included in ongoing research of work package 2.3 of the Horizon Europe CAMEO (CAMS EvOlution) project, which aims to develop an inversion of biogenic emissions within ECMWF’s Integrated Forecasting System (IFS). As a first step towards a successful implementation of HCHO assimilation and inversion capability within the IFS, a simplified HCHO chemistry scheme has been developed and is currently analyzed with a particular focus on its impact on other atmospheric reactive trace gases, such as isoprene and ozone, and on aerosols.