Flux-induced growth of atmospheric nano-particles by organic vapors

Description

Atmospheric aerosols strongly influence climate by changing the reflectivity and lifetime of clouds. Model simulations show that nearly half of the global cloud condensation nuclei in the atmospheric boundary layer may be formed through new particle formation. New particle formation consists of formation of thermodynamically stable clusters from trace gas molecules (homogeneous nucleation) followed by growth of these clusters to a detectable size (~3 nm). While many studies indicate that organics enhance the initial growth of the clusters and therefore new particle formation, it is suggested that the strong increase of surface equilibrium vapor concentration due to cluster curvature (Kelvin effect) may prevent ambient organics from condensing on these small clusters. Here, particle number flux due to heterogeneous nucleation, in which organic molecules condense on cluster surfaces to form critical embryos, is examined. We find that the flux induced by heterogeneous nucleation of organic vapors can effectively grow clusters substantially smaller than the Kelvin diameter, traditionally considered as the minimum particle size that can be grown through condensation. Including this flux leads to a factor of up to 300 increase in the predicted rates of new particle formation and the subsequent production of cloud condensation nuclei.