Aqueous-phase photochemical formation of hydroxyl radical in authentic cloudwaters and fogwaters

Aqueous-phase photochemical reactions initiated by simulated sunlight and 313-nm light form hydroxyl radical ( . OH) in authentic cloudwater and fogwater samples from various locations in the U.S. The quantum yields for . OH formation at 313 nm and the photoformation rates of . OH under sunlight conditions were quantified by the formation of phenol from the . OH-mediated oxidation of added benzene. Based on this technique, the measured photoformation rates of . OH several cloudwaters and fog-waters ranged from 0.32 to 3.0 μM h −1 under midday equinox sunlight conditions. These rates of aqueous-phase . OH photoformation are of the same magnitude as previously published estimated rates of . OH incorporation from gas-to-drop partitioning of . OH and from the aqueous-phase decomposition of O 3 transfered from the gas to the drop