Molecular Composition of Monoterpene Secondary Organic Aerosol at Low Mass Loading

• Published in: Environmental science & technology Vol. 44; no. 20; pp. 7897 - 7902
• Main Authors: Gao, Yuqian, Hall, Wiley A, Johnston, Murray V
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.10.2010
• Subjects: Aerosols; Applied sciences; Chemical compounds; Chromatography, Liquid; Environmental Measurements Methods; Environmental science; Exact sciences and technology; Fourier transforms; Ions; Mass spectrometry; Monoterpenes - chemistry; Organic Chemicals - chemistry; Pollution; Scientific imaging; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry; Ozonolysis; High resolution; Photochemical oxidants; Hydrocarbon; Ozone; Secondary pollutant; Artefact; Liquid chromatography; Volatile organic compound; Electrospray; Terpene; Ionization; Mass spectrometry MS/MS; Aerosols; Monoterpene; Air pollution; Reactor; Mass spectrometry; Organic compounds; Particle number
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es101861k

The molecular composition of secondary organic aerosol (SOA) from the ozonolysis of monoterpenes (α-pinene and β-pinene) was studied by liquid chromatography mass spectrometry and high-resolution Fourier transform ion cyclotron resonance mass spectrometry techniques, both employing electrospray ionization (ESI). SOA particles were generated in a flow tube reactor with a reaction time of 23 s. A microsampling assembly in combination with ESI-FTICR analysis permitted SOA with a mass loading as low as 3.5 μg/m3 to be characterized with high accuracy and precision mass analysis. Hundreds of product molecular formulas were identified that were common to all mass loadings; however the relative intensities changed significantly. In particular, a species with the (neutral molecule) formula C17H26O8 increased substantially in intensity relative to other products as the mass loading decreased. Tandem mass spectrometry (MSn) of this species showed it to be a dimer of C9H14O4 and C8H12O4, most likely pinic acid and terpenylic acid, respectively. LCMS analysis showed different elution times for the dimer and monomer species, confirming that the dimer was not an artifact of ESI analysis. The particle number concentration increased linearly with ozone concentration (the limiting reactant in the experiment), arguing against gas phase dimerization as the rate limiting step in particle formation.