Influence of Lowering Soot‐Water Contact Angle on Ice Nucleation of Ozone‐Aged Soot

Organic‐lean and organic‐rich size‐selected soot particles were exposed to a varying O 3 concentration, progressively decreasing the soot‐water contact angle ( θ ) to study its impact on ice nucleation (IN). The IN ability of fresh and O 3 ‐aged soot between 218 and 233 K was observed while monitoring the particle mass and size distributions. The properties of fresh and O 3 ‐aged bulk organic‐lean soot samples with a low and high O 3 ‐adsorption were characterized for soot‐water θ , chemical composition, functional groups, soot‐water interaction ability and porosity. By retaining the soot porosity between aged and unaged samples, we demonstrate that a decrease in θ after O 3 ‐aging enhances organic‐lean soot IN via pore condensation and freezing. Fresh organic‐rich soot exhibits suppressed homogeneous freezing, but after O 3 ‐aging it freezes within uncertainty of the homogeneous freezing threshold of solution drops, because of increased hydrophilicity.