Advanced Applications of Cloud Condensation Nuclei Activity
The cloud condensation nuclei (CCN) activity of both primary and secondary sources of aerosol was studied to gain a deeper understanding of how aerosols affect climate and health. CCN from secondary organic aerosol (SOA) was studied in four different systems: longifolene, isoprene, amines and uncombusted gasoline. Primary aerosol from electronic cigarette (E-cig) liquids was also studied.
The CCN activity of longifolene SOA increased over time, but could not be seen with the use of the typical κ-hygroscopicity parameter. To further investigate the cause of this, volatility data was taken at various thermodenuder temperatures and then used to model the formation of reaction products. Modeling showed that extremely low volatility organic compounds (ELVOCs) are produced via this pathway.
To further investigate changing hygroscopicity of SOA, isoprene SOA and isoprene + longifolene SOA was studied in addition to longifolene. The CCN/CN ratio of 100 nm particles at ~0.2% supersaturation was plotted, resulting in a sigmoid indicative of a critical time, at which 50% of the particles activated. This plot and critical time were then recreated using gas-phase decay data of the precursors, resulting in a similar sigmoid that predicted the critical time within 0.15 hours of the initial critical times. This indicates that gas phase vapors may influence CCN activation and changing hygroscopicity.
The potential health effects of aerosols produced by electronic cigarettes was studied by atomizing dilute E-cig liquid into a scanning mobility particle sizer (SMPS) coupled with a CCN counter. Flavorings were found to effect the enhanced condensational growth (ECG) potential, and mass spectra of the liquids also showed significant differences in the composition of the liquids.
The hygroscopity of amines was studied in 2 methods: temperature changes and alcohol amines. Temperature effects the evaporation of salts that form from amine oxidation. Hygroscopicity cannot be predicted using average molecular weights from the PiLS-ToF-MS.
The CCN potential of uncombusted gasoline was studied relative to commercial blends. Hygroscopicity was dependent on blend and changed over time for one commercial blend, but not the other, indicating not all fuel blends have the same CCN activity.