Laboratory study on new particle formation from the reaction OH + SO₂: influence of experimental conditions, H₂O vapour, NH₃ and the amine tert-butylamine on the overall process

The exponent for H₂SO₄ from different measurement series was in the range of 1.7-2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H₂O vapour was found to be 3.1 representing an upper limit.

Addition of 1.2×10¹¹ molecule cm⁻³ or 1.2×10¹² molecule cm⁻³ of NH₃ (range of atmospheric NH₃ peak concentrations) revealed that NH₃ has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions, i.e. a rise of the particle number by 1-2 orders of magnitude at RH = 13% and only by a factor of 2-5 at RH = 47% (NH₃ addition: 1.2×10¹² molecule cm⁻³).

Using the amine tert-butylamine instead of NH₃, the enhancing impact of the base for nucleation and particle growth appears to be stronger. Tert-butylamine addition of about 10¹⁰ molecule cm⁻³ at RH = 13% enhances particle formation by about two orders of magnitude, while for NH₃ only a small or negligible effect on nucleation in this range of concentration appeared. This suggests that amines can strongly influence atmospheric H₂SO₄-H₂O nucleation and are probably promising candidates for explaining existing discrepancies between theory and observations.