No abstract

Abstract. Recently, liquid–liquid phase separation (LLPS) of secondary organic aerosol (SOA) particles free of inorganic salts has been intensively studied due to the importance of cloud condensation nuclei (CCN) properties. In this study, we investigated LLPS in four different types of SOA particles generated from α-pinene ozonolysis and α-pinene photooxidation in the absence and presence of ammonia (NH3). LLPS was observed in SOA particles produced from α-pinene ozonolysis at ∼95.8 % relative humidity (RH) and α-pinene ozonolysis with NH3 at ∼95.4 % RH. However, LLPS was not observed in SOA particles produced from α-pinene photooxidation and α-pinene photooxidation with NH3. Based on datasets of the average oxygen to carbon elemental ratio (O:C) for different types of SOA particles from this study and from previous studies, there appears to be a relationship between the occurrence of LLPS and the O:C of the SOA particles. When LLPS was observed, the two liquid phases were present up to ∼100 % RH. This result can help more accurately predict the CCN properties of organic aerosol particles.

No abstract

An indoor smog chamber facility has been built for carrying out secondary organic aerosol (SOA) formation and for studying physicochemical properties of SOA. This facility comprises of ~7 m 3 FEP Teflon reactor placed in temperature controlled room coupled with instruments for gas and particle phase data. Detailed characterization experiments have been presented describing control of reactor temperature, relative humidity (RH), effective mixing time, wall loss rates of gases and particles, light source, and air purification. This chamber showed a wide range of temperature control with acceptable precision (i.e., 18-33 ± 0.5°C). The gas wall loss rates for NO, NO 2 , and O 3 were found to be 3.78 × 10 -4 min . Particle wall loss constant was found to be 3.96 × 10 -3 min -1 at D p = 100 nm. SOA yields of dark α-pinene ozonolysis ranged from 0.025 to 0.378 for α-pinene concentrations from 10 ppb to 100 ppb.

No abstract