Kinetics of aerosol formation in irradiated gaseous NO2–SO2 mixtures

We observe in gaseous mixtures of NO2 and SO2 the formation of white particles upon irradiation with 488 nm laser light and have measured the time of irradiation necessary for first detecting visually these particles at various total pressures, mole ratio of SO2 to NO2, and light intensities. A proposed simple reaction mechanism, up to the first reaction step of photoexcited NO2 and SO2, is consistent with the observations. The quenching coefficient of NO2* by SO2 is 5.7×1013 cm3/mole sec and the coefficient of the assumed rate-determining initial step, NO2*+SO2, is 8.2×1010 cm3/mole sec.