Improving our understanding of aerosol formation, transformation and lifetime in controlled atmospheres

Gas-particle partitioning is an essential property of secondary organic aerosol (SOA) and is
dependent on the vapour pressure of a specific compound. Group contribution methods
have been developed to model saturation vapour pressures, but these predictions are
unvalidated for many atmospherically relevant SOA. In this research, single-particle
levitation will be used for the experimental determination of pure component vapour pressure
via electrodynamic balance of a binary droplet, which will be validated against model
predictions in UManSysProp. Accurate quantification of the partitioning properties of aerosol
can contribute towards our ability to detect the presence of aerosol vapour in relevant
conditions. Gas-particle partitioning measurements are relevant towards detecting trace
components, for example, in explosive detection. Current techniques assume that the air
sampled is only gaseous. However, recognising that the trace components can be between
the gas and particle phase suggests that detecting the condensed phase can lead to
enhanced sensitivity of detection methods. This is due to the partitioning of the aerosol
concentrating the amount of analyte into the condensed phase. Previous work has provided
preliminary data to examine the concentrating effect of aerosol, for example, a solid trace
explosive surrogate analyte was allowed to equilibrate in a permeation oven of a chosen
temperature (<55C/328.15K) and vapour was collected by a porous polymer sorbent
(TenaxTM). The outflow of vapour was quantified and characterised by TD-GC-MS. To
incorporate the concentrating effect of aerosol, Tween-20 as a compound will be used as a
surrogate for ambient particles, allowing the study of the accretion of a semi-volatile
component from an explosive and thus providing an enhancement in detection sensitivity.