Investigating the chemical composition of mixed organic–inorganic particles by “soft” vacuum ultraviolet photoionization: The reaction of ozone with anthracene on sodium chloride particles

The ozone reaction with anthracene coated sodium chloride particles is measured by single photon ionization of the resulting volatilized gas phase molecules. To investigate in detail the organic fraction of particles, a vacuum ultraviolet aerosol mass spectrometer (VUV-AMS) has been developed at the Chemical Dynamics Beamline at the Advanced Light Source. This instrument combines a thermal vaporization particle source with tunable synchrotron radiation. Since VUV is a “soft” ionization method, the roles of both the vaporization and ionization steps on the fragmentation patterns of C30H62 hydrocarbons are observed. Conditions can be found to obtain mass spectra without significant fragmentation of the molecules. This technique is used to characterize the products of the heterogeneous reaction of gas phase ozone with particle phase anthracene on size-selected sodium chloride particles, conducted in a flow tube experiment. The recorded fragment-free mass spectra show several new products from mono- to penta-oxygenated anthracene. The kinetics of the product formation and particle size measurements are simultaneously recorded, revealing that an increase of the particle size accompanies the formation of the products.