Seasonal isoprene emission estimates over tropical South America inferred from satellite observations of isoprene

Abstract. Isoprene, a volatile organic compound (VOC) emitted by plants, plays a significant role in atmospheric chemistry and climate. The Amazon rainforest is a globally-relevant source of atmospheric isoprene, influencing regional and global atmospheric composition. We report isoprene emissions for 2019 inferred from the Cross-track Infrared Sounder (CrIS) and the local sensitivities between isoprene emissions and isoprene columns determined by the GEOS-Chem chemical transport model. Compared with the MEGAN bottom-up inventory of isoprene emissions, the isoprene emission estimates inferred from CrIS have different spatial and seasonal distributions with generally lower emission rates but with higher emission rates over the north of Amazon basin and southeast of Brazil. Isoprene mole fraction data collected at the Amazon Tall Tower Observatory (ATTO) are invaluable for evaluating isoprene emission estimates. The observed mean isoprene concentration at ATTO, March—December 2019, is 3.0 ± 2.2 ppbv, which is reproduced better by the GEOS-Chem model driven by isoprene emissions inferred from CrIS (2.8 ± 1.4 ppbv) than by the MEGAN inventory (4.1±1.3 ppbv). GEOS-Chem model formaldehyde (HCHO) columns, corresponding to isoprene emissions inferred from CrIS, are generally more consistent with TROPOMI data (normalized mean error, NME = 43 %) than the HCHO columns corresponding to MEGAN isoprene emissions (NME = 50 %), as expected. They also improve the model agreement with regional TROPOMI HCHO:NO2 column ratios that are indicative of changes in photochemical regime. Our results provide confidence that we can use CrIS data to examine future impacts of anthropogenic activities on isoprene emissions from the Amazon.