On-line fast analysis of light hydrocarbons, PAH and radicals by molecular-beam time of flight mass spectrometry

Volatile organic compounds (VOC) and polycyclic aromatic hydrocarbons (PAH), emitted in the environmentfrom a wide range of combustion sources, are hazardous to human health and consideredimportant precursors of both primary and secondary particulate pollutants. In the present work, lighthydrocarbons up to C9, as main components of combustion-derived VOC, and PAH produced in fuel-richconditions of premixed ethylene flames were analyzed by implementing a molecular-beam time of flightmass spectrometer (MB-TOFMS), purposely built for on-line fast monitoring of the environmental impactof combustion systems. The reliability of the MB-TOFMS was preliminarily verified on a slightly-sootingflame, comparing the results with those obtained by batch sampling and gas chromatographic techniques.Electron ionization (EI) and multi-photon ionization (MPI) were used as MB-TOFMS sources andtested on combustion gases of a no-sooting premixed ethylene flame where VOC and PAH are present intraces not detectable with batch sampling and conventional analytical techniques. The mass identificationaccuracy was improved and guaranteed by systematically performing internal mass calibration,exploiting the formation of "in situ" clusters from combustion water in the molecular beam apparatus.Selective and sensitive monitoring of light hydrocarbons and PAH, derived from oxidation and pyrolysisreactions featuring combustion, was shown to be especially effective when using the MB-TOFMSequipped with MPI source. This technique showed to be effective also for the detection of radical speciesthat are important for the risk assessment of aerosol and fundamental understanding of aerosolchemistry at a molecular level.