10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Refining Equilibrium Partitioning: Detailed Chemical Composition, Viscosity and Diffusion Measurements
KELLY PEREIRA, Alfie Mayhew, Grazia Rovelli, Young-Chul Song, Aleksandra Marsh, Stephen Ingram, Simon O'Meara, David Topping, Jonathan P. Reid, Jacqueline F. Hamilton, University of York
Abstract Number: 839 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) constitutes a considerable proportion of ambient particulate matter and exhibits substantial chemical complexity. Equilibrium partitioning is a fundamental theorem governing the growth and loss of SOA. However, recent literature has suggested that gas-particle partitioning may be kinetically limited, preventing volatilisation from the SOA due to the physical state of the particle (e.g. viscous, glassy). To predict the properties and impacts of SOA in the atmosphere, the processes controlling non-equilibration must be known. This work combines several key components to investigate the effect of the physical state of the SOA on equilibrium partitioning, including detailed chemical speciation and bulk compositional measurements, single particle viscosity/diffusion measurements and modelled simulations for the refinement of predictive tools for multicomponent mixtures.
Experiments were performed in a 300L in-house built continuous flow reactor. Over 50 experiments were performed, investigating SOA formation from the photo-oxidation of α-pinene, β-caryophyllene, limonene and toluene under varying %RH, NOx and VOC mixing ratios. SOA mass was collected using an electrical low pressure impactor, minimising potential artefacts associated with conventional filter extraction methods. SOA composition was investigated using a variety of state-of-the-art techniques, including ultra-high performance liquid chromatography ultra-high resolution mass spectrometry, 1H and two-dimensional 1H-13C heteronuclear single quantum correlation (HSQC) nuclear magnetic resonance spectroscopy, Fourier transform infra-red spectroscopy and CHNS elemental analysis. High performance liquid chromatography ion trap mass spectrometry coupled to an automated fraction collector was also used for the isolation and collection of individual compounds in α-pinene SOA, providing authentic standards for quantification. Up to 40% of the generated α-pinene SOA mass (by weight) has been quantified, with a range of 3 to 40% depending on experimental conditions (e.g. with/without NOx). Bulk compositional techniques indicate subtle changes in the functionality of the SOA with varying %RH and NOx mixing ratios, which has little impact on bulk SOA metrics such as average carbon oxidation state. In contrast, individual α-pinene SOA species displayed marked differences in their concentrations during the same experiments. This suggests that the metrics that describe bulk SOA properties are rather insensitive to molecular levels changes, possibly as a result of the production of similar functionalities under varying chamber conditions. Detailed compositional data combined with viscosity and diffusion measurements has the potential to lead to considerable advances in our understanding of the dynamic mechanisms controlling equilibrium partitioning. To our knowledge, this is first study which has combined both detailed chemical composition, viscosity/diffusion measurements and multicomponent model simulations.