Satellite Observations of Isoprene from the Thermal Infrared Imaging Spectrometer: From Cross-track Infrared Sounder towards a Next Generation of Global Observing System

Isoprene (C₅H₈), the most important of the non-methane biogenic volatile organic compounds, plays a crucial role in atmospheric chemistry: by affecting the oxidative capacity of the atmosphere through reaction with OH, and as an important precursor of O₃ and secondary organic aerosols. Its annual emissions have been estimated at 270–1,000 TgC (overwhelmingly from terrestrial plants), which is equivalent to the size of the annual biogenic CH₄ source. Accurate isoprene measurements from airplane and surface sites are sparse. Top-down constraints on the global distribution of isoprene sources have relied on an indirect approach using its oxidation product formaldehyde (HCHO). However, such estimates suffer from errors due to (1) the fact that HCHO is also derived from other volatile organic compounds, and (2) uncertainty in the isoprene-formaldehyde relationship and spatial smearing between the two. This has led to an ambiguous understanding of the various factors controlling the spatial and temporal distribution of isoprene.

Direct measurements of global atmospheric isoprene are needed to improve quantification of isoprene’s roles in atmospheric chemistry and the carbon cycle. We will present retrievals of atmospheric isoprene directly from existing CrIS satellite observations across its n₂₇ and n₂₈ spectral bands (860 to 940 cm^-1) over the Amazonian forest, as well as an evaluation of the results using a combination of in-situ measurements and GEOS-Chem modeling. Furthermore, we will report the results from recent Observation System Simulation Experiments (OSSEs) that investigate the measurement requirements for a next-generation global observing system (GOS), aiming at new capabilities for quantifying atmospheric isoprene across all seasons over the globe.