Condensation nuclei supersaturation spectrum: analysis of the relationship between the saturation droplet radius and the critical supersaturation in the Laktionov isothermal chamber

Computations testing the uniqueness of the relationship between the saturation droplet radius r100 and the critical supersaturation S, have been performed for condensation nuclei (CN) of different chemical composition: pure salts, mixtures of salts and partly insoluble nuclei; indeed, the reliability of this relationship is the key-point in determining the CN supersaturation spectrum by an isothermal chamber. The results show that in the case of typical natural inorganic aerosols the dependence of Sc, on r100 is practically unique for all the CN considered, as the uncertainty in the CN electrolytic composition can lead to a maximum error of about 8% on the activated nuclei counts; by using Laktionov's relationship this error can reach about 12%. When surface-active organic materials are present, the relationship between r100 and S,. is significantly modified ; the activated nuclei counts can differ, for continental aerosols, up to +100% from the corresponding counts of pure inorganic aerosols. Also a decrease in nuclei counts can be predicted ; values up to — 80% have been determined. In conclusion, when the Laktionov isothermal chamber is used, simultaneous measurements characterizing the organic materials are required for an accurate determination of the CN supersaturation spectrum.