Effects of Organic Water on Inorganic Aerosol Thermodynamics

Stylianos Kakavas, Athanasios Nenes, SPYROS PANDIS, University of Patras

     Abstract Number: 249
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
In this work we present the effects of secondary organic aerosol water (SOAW) on inorganic aerosol thermodynamics. Organic aerosol although less hygroscopic than inorganic, could also contribute significantly to the total atmospheric aerosol water levels (Guo et al., 2015). The added water mass can induce secondary inorganic aerosol formation since more of the gas phase components partition to the aerosol to satisfy equilibrium (e.g., Ansari and Pandis, 2000). These feedbacks are usually not considered in chemical transport models simulations.

For that purpose, we use a new developed inorganic aerosol thermodynamics module, ISORROPIA-lite (Kakavas et al., 2022), an accelerated and simplified version of the widely used ISORROPIA-II (Fountoukis and Nenes, 2007), which considers secondary organic aerosol water to thermodynamic equilibrium and assumes that the aerosol is in metastable equilibrium (aerosol exists only in liquid form) using binary activity coefficients from precalculated tables. We used ISORROPIA-lite in PMCAMx chemical transport model simulations over Europe and continental United States to study organic aerosol water effects.

Simulations considering the effects of secondary organic aerosol water show average increases of the concentrations of the inorganic semivolatile components and especially that of nitrate within 0.25 μg m⁻³ over continental Europe and US. However, the temporal evolution shows that except organic water could highly contribute to the total PM₁ water mass, can also increase the concentrations of fine nitrate and ammonium within 1.5 μg m⁻³ in places where secondary organic aerosol and RH levels are high.

References
[1] Ansari, A. S. and Pandis, S. N. (2000) Environ. Sci. Technol. 34, 71–77.
[2] Fountoukis, C. and Nenes, A. (2007) Atmos. Chem. Phys. 7, 4639-4659.
[3] Guo, H., Xu, L., Bougiatioti, A., Cerully, K. M., Capps, S. L., Hite Jr., J. R., Carlton, A. G., Lee, S.-H., Bergin, M. H., Ng, N. L., Nenes, A., and Weber, R. J. (2015) Atmos. Chem. Phys. 15, 5211–5228.
[4] Kakavas, S, Pandis, S. N. and Nenes, A. (2022) Tellus B, 74, pp. 1-23.