Acidity effects on the formation of α-pinene ozone SOA in the presence of inorganic seed

A 2 m3 chamber was used to explore the effect of relative humidity (RH) and inorganic composition on aerosol yield due to aerosol phase heterogeneous processes in the α-pinene ozone oxidation system. The inorganic compositions considered range from pure aqueous sulfuric acid to a completely neutralized acid, ammonium sulfate. The heterogeneous organic mass (OMH) and the organic mass from partitioning (OMP) were decoupled from the total organic mass to consider the effect of acidity parameters solely on the aerosol mass fraction they impact the most (OMH). An experiment with aqueous ammonium sulfate was preformed in a 25 m3 chamber to determine the distribution of α-pinene ozone products for an explicit multiproduct model used in the decoupling process. Both RH and inorganic seed composition were found to influence heterogeneous aerosol yield, due to the acid catalytic nature of the reactions that lead to this mass. The highest heterogeneous aerosol yields were found under conditions of low RH and strongly acidic inorganic seed compositions. A multiple linear regression model is presented and analyzed to show that both RH and inorganic seed composition significantly influence the production of aerosol mass through heterogeneous processes. The results presented here aid our understanding of the development of heterogeneous mass in the presence of inorganic aerosols and will be useful for modeling heterogeneous aerosol mass.