We report water aerosol formation upon irradiation of wet air with a KrF laser at 248 nm. It occurred at temperatures ranging from 0 to 50 °C and at relative humidity values from ca. 10% to 100%. Aerosols were detected either by light scattering or by differential mobility analyses, and particle growth from 10 nm to sub-micrometers was observed. Photodissociation of oxygen was proposed as the initial step of the reactions leading to formation of the final stable molecule of hydrogen peroxide as a nucleus with a low vapor pressure. Simulations of the chemical kinetics by considering wet air revealed that the amount of the final product could be controlled by laser operational conditions such as laser repetition rates and pulse energies. KrF laser light can reach a few kilometers in the atmosphere owing to a small absorption cross section of oxygen and yet can produce water aerosol.
2012 The Chemical Society of Japan