Effect of solubility limitation on hygroscopic growth and cloud drop activation of SOA particles produced from traffic exhausts

Research output: Contribution to journalArticle


Hygroscopicity measurements of secondary organic aerosol (SOA) particles often show inconsistent results between the supersaturated and subsaturated regimes, with higher activity as cloud condensation nucleus (CCN) than indicated by hygroscopic growth. In this study, we have investigated the discrepancy between the two regimes in the Lund University (LU) smog chamber. Various anthropogenic SOA were produced from mixtures of different precursors: anthropogenic light aromatic precursors (toluene and m-xylene), exhaust from a diesel passenger vehicle spiked with the light aromatic precursors, and exhaust from two different gasoline-powered passenger vehicles. Three types of seed particles were used: soot aggregates from a diesel vehicle, soot aggregates from a flame soot generator and ammonium sulphate (AS) particles. The hygroscopicity of seed particles with condensed, photochemically produced, anthropogenic SOA was investigated with respect to critical supersaturation (sc) and hygroscopic growth factor (gf) at 90% relative humidity. The hygroscopicity parameter κ was calculated for the two regimes: κsc and κgf, from measurements of sc and gf, respectively. The two κ showed significant discrepancies, with a κgfsc ratio closest to one for the gasoline experiments with ammonium sulphate seed and lower for the soot seed experiments. Empirical observations of sc and gf were compared to theoretical predictions, using modified Köhler theory where water solubility limitations were taken into account. The results indicate that the inconsistency between measurements in the subsaturated and supersaturated regimes may be explained by part of the organic material in the particles produced from anthropogenic precursors having a limited solubility in water.


External organisations
  • Scania’s Association of Local Authorities (Kommunförbundet Skåne)
  • Research Institutes of Sweden (RISE)
  • University of Applied Sciences and Arts Northwestern Switzerland (FHNW)
  • SWECO Environment AB
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Meteorology and Atmospheric Sciences
  • Environmental Sciences


  • Critical supersaturation, Hygroscopic growth, Particles, SOA, Solubility, Traffic exhausts
Original languageEnglish
Pages (from-to)359-383
JournalJournal of Atmospheric Chemistry
Issue number4
Early online date2018 Nov 23
Publication statusPublished - 2018 Dec
Publication categoryResearch