HYGROSCOPIC PROPERTIES OF CARBON AND DIESEL SOOT PARTICLES

Laboratory experiments were performed in order to study the hygroscopi c properties of freshly produced carbon and diesel soot particles at s ubsaturations (i.e. at relative humidity < 100%). Wetted carbon aggreg ates collapsed to a more compact structure. In contrast, the diesel co mbustion particles exhibited a much smaller restructuring combined wit h condensational growth. The hygroscopicity of the diesel particles wa s enhanced when the sulfur content of the fuel was increased or when t he particles were subjected to an ozone and UV pre-treatment. By extra polating the data with a Kohler model critical supersaturations were c alculated. Freshly emitted combustion particles are unlikely to act as cloud condensation nuclei whereas an aging of the particles will enha nce their nucleation ability. (C) 1997 Elsevier Science Ltd.