Liquid–liquid phase separation in secondary organic aerosol particles produced from α -pinene ozonolysis and α -pinene photooxidation with/without ammonia

Abstract

Abstract. Recently, liquid–liquid phase separation (LLPS) of secondary organic\naerosol (SOA) particles free of inorganic salts has been intensively studied\ndue to the importance of cloud condensation nuclei (CCN) properties.\nIn this study, we investigated LLPS in four different types of SOA particles\ngenerated from α -pinene ozonolysis and α -pinene\nphotooxidation in the absence and presence of ammonia ( NH3 ). LLPS was observed\nin SOA particles produced from α -pinene ozonolysis at\n ∼95.8 \u2009% relative humidity (RH) and α -pinene\nozonolysis with NH3 at ∼95.4 \u2009%\u2009RH. However, LLPS was\nnot observed in SOA particles produced from α -pinene photooxidation\nand α -pinene photooxidation with NH3 . Based on datasets of the average\noxygen to carbon elemental ratio ( O:C ) for different types of SOA particles\nfrom this study and from previous studies, there appears to be a relationship\nbetween the occurrence of LLPS and the O:C of the SOA particles. When LLPS\nwas observed, the two liquid phases were present up to ∼100 \u2009%\u2009RH. This result can help more accurately predict the CCN\nproperties of organic aerosol particles.