Microstructural rearrangement of sodium chloride condensation aerosol particles on interaction with water vapor

The interaction of water vapor with submicron NaCl condensation aerosols ha s been investigated with a tandem differential mobility analyzer (TDMA) and compared to experiments with NaCl dispersion and PbS condensation aerosols . The mobility equivalent diameters of the NaCl condensation aerosol partic les decreased by up to 50% when exposed to relative humidities (RH) below t he deliquescence threshold. The extent of shrinking was determined by relat ive humidity, initial particle size (19-200 nm) and aerosol generation para meters. Above similar to 75% RH hygroscopic growth was observed in agreemen t with Kohler theory. Dynamic shape factors for the NaCl condensation aeros ol particles before and after humidification were calculated, indicating a transformation from sparse branched-chain to more compact agglomerates. The investigated PbS particles shrank much less but still significantly when e xposed to water vapor, which is discussed in View of the microstructural re arrangement processes at work. (C) 2000 Elsevier Science Ltd. All rights re served.