Characterisation of surfactants in PM1 aerosols from diffrent regions of Europe and correlations with cloud occurence
Résumé
The importance of the surface tension term of the Köhler equation in the activation of sub-micron particles into cloud droplets in the atmosphere has been evidenced by several works. But information on the compounds actually lowering the surface tension sub-micron particles (= “surfactants”) in the atmosphere remains scarce. This presentation reports the characterization of the surfactants present in PM1 aerosols in different regions of Europe: Lyon, France, Rogoznica, Croatia, and Pallas, Finland: concentrations in the air and in the particle volume, adsorption isotherms and Critical Micelle Concentration (CMC). At the remote site of Pallas, Finland, the surfactant concentrations and their correlations with the PM1 population and with other PM1 chemical components (inorganic ions) indicated that these compounds were present in the entire particle size distribution, not only in a few large particles, as it has been hypothesized. At all sites, and in nearly all samples, the CMC obtained from the surfactant adsorption isotherms was low (≤ mM) so that, combined with the observed concentrations, the surfactants found in these PM1 samples should strongly depress the surface tension of the sub-micron particles until activation (Growth Factor = 5 - 10), thus enhance their CCN ability.
In Pallas, the potential role of surfactants on cloud formation was also explored by performing statistical analyses between the surfactants properties in PM1 aerosols and cloud occurrence over 9 months (237 aerosol samples and 257 cloud events). The results will be presented.