Nocturnal survival of isoprene linked to formation of upper tropospheric organic aerosol.

Isoprene is emitted mainly by terrestrial vegetation and is the dominant volatile organic compound (VOC) in Earth's atmosphere. It plays key roles in determining the oxidizing capacity of the troposphere and the formation of organic aerosol. Daytime infrared satellite observations of isoprene reported here broadly agree with emission inventories, but we found substantial differences in the locations and magnitudes of isoprene hotspots, consistent with a recent study. The corresponding nighttime infrared observations reveal unexpected hotspots over tropical South America, the Congo basin, and Southeast Asia. We used an atmospheric chemistry model to link these nighttime isoprene measurements to low-NO x regions with high biogenic VOC emissions; at sunrise the remaining isoprene can lead to the production of epoxydiols and subsequently to the widespread seasonal production of organic aerosol in the tropical upper troposphere.