Upper limit for the UV absorption cross sections of H2SO4

An upper limit for the gas phase absorption cross sections for H2SO4 over the wavelength range 195 to 330 nm has been determined. Absorption measurements were made using a diode array spectrometer and a 100 cm long heated absorption cell. Gas phase H2SO4 was generated in a gas flow by titrating (equilibrating)known amounts of SO, via the reaction SO3 + H2O <----> H2SO4 (3) at elevated temperatures, similar to 500 K. Upper limits to the H2SO4 absorption cross sections were obtained, < 1 x 10(-21) cm(2) molecule(-1), and provide an upper limit to the atmospheric photolysis rate of H2SO4. The implications of this cross section limit to stratospheric sulfur chemistry are discussed.