Sulphuric acid aerosols in low oxygen environments

Experiments on sulphuric acid nucleation in low oxygen atmospheres were done in order to investigate the role of nucleation in the Archean atmosphere. Nucleation initiated by photolysis of SO₂ and subsequent reaction between atomic O and SO₂ was measured with a PSM and a separate CPC. The parameters were <10 ppm O₂ with varying levels of SO₂ (4 levels from 40 to 105 ppb), RH (3 levels from 0 to 51%), UV light (254 nm, 4 levels from 55 to 100% power), and ionization (2 levels: Background (∼3 cm⁻³ s⁻¹) and increased w. gamma sources (∼42 cm⁻³ s⁻¹)). We find that nucleation is possible under these conditions and that the measured formation rates correlate positively with all varied parameters. This suggests that the sulphuric acid nucleation system could have played a role in the Archean atmosphere.