Adsorption of organic molecules may explain growth of newly nucleated clusters and new particle formation

Abstract

New particle formation consists of homogeneous nucleation of thermodynamically stable clusters followed by growth of these clusters to a detectable size. For new particle formation to take place, these clusters need to grow sufficiently fast to escape coagulation with preexisting particles. Previous studies indicated that condensation of low-volatility organic vapor may play an important role in the initial growth of the clusters. However, due to the relatively high vapor pressure and partial molar volume of even highly oxidized organic compounds, the strong Kelvin effect may prevent typical ambient organics from condensing on these small clusters. Here we show that the adsorption of organic molecules onto the surface of clusters, not considered previously, may significantly reduce the saturation ratio required for the condensation of organics to occur and therefore may provide a physicochemical explanation for the enhanced initial growth by condensation of organics despite the strong Kelvin effect. © 2013 American Geophysical Union. All Rights Reserved.