Implications for Atmospheric Chemistry: Calculation of Cloud Activation Potential. Based on Kӧhler theory, the cloud condensation nucleation activity of aerosol particles depends on particle size and chemical composition, the latter being the determining factor for smaller particles. Surface-active species are of specific importance to cloud activation, given their propensity to depress the surface tension at the moment of particle nucleation. As a result, the water vapor supersaturation ratio needed for cloud activation is decreased. Following procedures laid out in our previous work inspired by that of the McNeil group, we calculated the critical supersaturation ratio required for CCN formation (𝑠 % * /𝑠 % ) for the dimer standards using the following equation: 68