Simultaneously Characterizing the Volatility Distribution and Phase State of Submicron Secondary Organic Aerosols Using a Vocus Vaporization Inlet for Aerosols with a Chemical Ionization Mass Spectrometer

Volatility and viscosity are important parameters affecting the formation, reaction, and fate of atmospheric organic aerosols. In this study, a Vaporization Inlet for Aerosol (VIA) coupled with a Vocus chemical ionization mass spectrometer (Vocus-CIMS) using NH₄⁺ adduct ionization is employed to simultaneously detect and quantify the molecular composition and volatility of organic aerosols through a program-controlled temperature ramp, thereby providing viscosity information. Volatility calibration was conducted with a series of reference aerosol particles with different chemical compositions, covering a vapor pressure range from 10^–1 to 10^–8 Pa. Secondary organic aerosols (SOA) produced from the potential aerosol mass reactor were analyzed by the VIA-CIMS. Chemical species ranging from semivolatile to low-volatility, including highly oxygenated dimers, were identified. Individual ions from the collected mass spectra were fitted and grouped by volatility basis sets to yield the volatility distribution of the SOA, allowing for the quantification of the glass transition temperatures and viscosities. Results show that β-caryophyllene ozonolysis SOA has lower volatility and is more viscous than the α-pinene SOA. This approach enables the online quantification of SOA particle chemical composition and volatility distribution, while simultaneously characterizing particle phase state, such as viscosity and water diffusion time, providing crucial insights into their chemical processes and climate impacts.