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Updated: Jun 8, 2026

Production and Measurement of Organic Particulate Matter in the Harvard Environmental Chamber
Published on: November 18, 2018
Molecular composition of monoterpene secondary organic aerosol at low mass loading
Yuqian Gao1, Wiley A Hall, Murray V Johnston
1Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
Abstract:
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/m(3) 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 C(17)H(26)O(8) increased substantially in intensity relative to other products as the mass loading decreased. Tandem mass spectrometry (MS(n)) of this species showed it to be a dimer of C(9)H(14)O(4) and C(8)H(12)O(4), 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.
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