Volatility of molecular components of aPinene SOA modulated by inorganic seed composition

The effective saturation vapor concentration (Log C*_eff) of a molecule represents an important variable that governs the ability of molecule to nucleate new particles and partition into pre-existing aerosols. Thus, the saturation vapor concentration affects the chemical composition and the mass yields of ambient aerosol, ultimately affecting air pollution and climate.¹ The determination of saturation vapor concentration is straight forward for small molecules, and those readily synthesized. However, the oxidation of volatile organic compounds creates a complex mixture of molecules, which is not easily separated to determine their saturation vapor concentration. Furthermore, SOA can often be mixed with other particles, containing species such as inorganic salts (e.g., ammonium sulfate) or mineral dust, impacting the non-ideality of the aerosols.

 

A thermal denuder coupled to a scanning mobility particle sizer (TD-SMPS) has been employed to determine the saturation vapor concentration of single component systems.² However, the lack of chemical resolution prevents its applicability to determine the saturation vapor concentration of more complex organic mixtures such SOA.³ Consequently, considerably uncertainties still exists regarding the saturation vapor concentration of ambient SOA components. To address this issue, here we deployed an extractive electrospray ionization mass spectrometer (EESI-MS) coupled with a TD-SMPS (hence TD-SMPS+EESI) to provide molecular formula separation of complex mixtures together with their saturation vapor concentrations.⁴ We performed measurements on a complex mixture of known species (PEG-300) to demonstrate the ability to extract the saturation vapor concentration. We have generated SOAs derived from the ozonolysis of α-pinene in an atmospheric simulation chamber to extract their C*_eff’s under three conditions: without seeds present, with ammonium sulfate seeds, and with a mixed iron/ammonium sulfate seeds. The presence of seed modulates the extracted C*_eff values from SOA samples, suggesting there are non-ideal interactions between the underlying seed. Further, the presence of iron in the seed significantly exacerbates these non-ideal interactions, which indicates that knowing the underlying seed composition is important for understanding C*_eff.

References:

 

(1) Ciarelli, G.; Haddad, I. E.; Bruns, E.; Aksoyoglu, S.; Möhler, O.; Baltensperger, U.; Prévôt, A. S. H. Constraining a hybrid volatility basis-set model for aging of wood-burning emissions using smog chamber experiments: A box-model study based on the VBS scheme of the CAMx model (v5.40). Geosci. Model Dev. 2017, 10 (6), 2303-2320. DOI: 10.5194/gmd-10-2303-2017.

(2) Kostenidou, E.; Karnezi, E.; Kolodziejczyk, A.; Szmigielski, R.; Pandis, S. N. Physical and Chemical Properties of 3-Methyl-1,2,3-butanetricarboxylic Acid (MBTCA) Aerosol. Environmental Science & Technology 2018, 52 (3), 1150-1155. DOI: 10.1021/acs.est.7b04348.

(3) Cappa, C. D.; Wilson, K. R. Multi-generation gas-phase oxidation, equilibrium partitioning, and the formation and evolution of secondary organic aerosol. Atmos. Chem. Phys. 2012, 12 (20), 9505-9528. DOI: 10.5194/acp-12-9505-2012.

(4) Bell, D. M.; Zhang, J.; Top, J.; Bogler, S.; Surdu, M.; Slowik, J. G.; Prevot, A. S. H.; El Haddad, I. Sensitivity Constraints of Extractive Electrospray for a Model System and Secondary Organic Aerosol. Analytical Chemistry 2023, 95 (37), 13788-13795. DOI: 10.1021/acs.analchem.3c00441.