Real-Time Probing of Atmospheric Photochemical Reaction by Ultrashort Eextreme Ultraviolet Pulses: Nitrous Acid Release from o-Nitrophenol

O rtho nitrophenol (NP) is produced by the combustion of wood or coal and are widely distributed in the gas phase and in organic aerosols in the atmosphere [1] . The photolysis of NP is considered as a source of nitrous acid (HONO). HONO is known for early-morning photochemical generation of OH radicals, which are responsible for ozone formation and photochemical smog. Therefore, NP can be considered as a key pollutant, whose photochemistry needs to be understood. We investigate the photolysis of o -NP by time-resolved photoelectron spectroscopy using extreme ultraviolet (EUV) femtosecond pulses and reveal the dissociation dynamics summarized in Fig. 1 including the structures of key intermediates [2] .