The following study extends previous work on modelling multicomponent surface tensions and the impact they have on aerosol and climate modelling. Mixed dicarboxylic acid and ammonium sulfate solution surface tensions have been measured experimentally and were modelled using an additive, a semi-empirical and two thermodynamic methods. A thermodynamic method with parameters fitted to binary solution data reproduced experimental results most closely with average absolute deviation from the experimental data over all measurements of 2.6%, compared with 7.7% for the additive, 8.1% for the semi-empirical and 7.3% for the other thermodynamic method. The choice of surface tension modelling method can lead to differences of up to 50% in the critical saturation ratios of aerosol particles. When applied to a trimodal aerosol distribution this leads to a difference in dry diameter for activation of 30 to 40 nm. This is greater than the difference induced by changing inorganic to organic mass ratios (>10 nm).