Cloud droplet activation of polymerized organic aerosol

High-molecular-weight organic compounds represent an important fraction in atmospheric aerosols, but their interactions with atmospheric water vapour are not well understood. Specifically, the hygroscopicity of polymerized atmospheric aerosols is larger than expected for their high molecular weights and is not a strong function of the degree of polymerization, but their cloud-nucleating activity declines as polymerization progresses.We apply a Flory–Huggins based theory for polymer–water interactions to describe water activity in aqueous solutions of atmospherically relevant oligomers and polymers, and show via experiments on particles composed of commercial polymers that it is consistent with observed particle hygroscopic growth and cloud formation behaviour