The theoretical study of the degradation pathways of organic compounds in the troposphere after photoexcitation in the gas phase or in water droplets is performed by density functional theory (DFT). The theoretical results assist in the rationalization of experimental findings in collaboration with the group of Prof. Sasho Gligorovski in the State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences. Small molecules including pyruvic acid and fluorene (J. Geophys. Res.: Atmospheres 2020, 125, e2019JD031839) have so far been considered.