Molecular characterization of monoterpene ozonolysis products using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry

Abstract

A detailed knowledge of the chemical composition of secondary organic aerosols (SOA) is required to better understand their roles in climate change, biogeochemical cycling and public health. The chemical composition of the SOA produced by the ozonolysis of limonene was investigated using electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR) mass spectrometry. SOA was generated in a 1.5 m3 teflon chamber with 500 ppb of limonene and 250 ppb of O3, without the presence of hydroxyl radical scavenger. We have identified approximately 1300-1500 molecular masses from negative-ion spectra in the range of 105 \u3c m/z \u3c 870 in each of two samples. The double bond equivalency (DBE), the number of rings and unsaturated bonds, values range from 1 to 13. This indicates the formation of a wide variety of chemical compounds. Several regions of high peak number density were observed in the mass ranges of 170 \u3c m/z \u3c 280, 350 \u3c m/z \u3c 480, 550 \u3c m/z \u3c 650 and 730 \u3c m/z \u3c 850. These regions are generally referred to as monomers, dimers, trimers, and tetramers of oxidized monoterpene units. The average DBE values for monomer to tetramer regions increase from 3.7 to 9.4 and the oxidation number decreases from -0.4 to -0.7. These results suggest that high MW organic compounds in the SOA samples are more unsaturated and less-oxidized. Both the oxygen to carbon (0.2-2) and hydrogen to carbon (0.5-1.1) ratios for limonene-SOA are different from those for α-pinene-SOA, 0.2-1 and 1.1-1.9 (Putman et al., 2010). We will compare the chemical composition of limonene-SOA with that of α- and β-pinene-SOA. We will also discuss the MSn fragmentation behavior of major ions for the structural elucidation of the oligomers