[A-AS04] Atmospheric Chemistry

[AAS04-22] LC/MS analysis of molecular markers present in biogenic secondary organic aerosols collected during year-round observations at a cool-temperature forest

*Kei Sato¹, Sathiyamurthi Ramasamy¹, Satoshi Inomata¹, Yuzo Miyazaki² (1.National Institute for Environmental Studies, 2.Hokkaido University)

Keywords:Bigenic volatile organic compound, Secondary organic aerosol, Organosurfate, Nitrooxy organosulfate, Organic nitrogen

To understand formation processes for organic nitrogen and dimeric compounds present in forest aerosols, we analyzed molecular markers present in forest aerosols collected during year-round observations using negative/mode electrospray ionization-liquid chromatography-mass spectrometry (ESI-LC/MS). Thirty-seven aerosol filter samples were collected at Tomakomai Experimental Forest between January and December in 2013, and 33 of the collected samples were analyzed in this study. Molecular markers analyzed in this study were cis-pinic acid, 3-methyl-1,2,3-butanetricarboxylic acid (3-MBTCA), α-pinene-derived dimer detected by ESI at m/z 357 (α-pinene dimer), isoprene-derived olganosulfate detected at m/z 215 (isoprene OS), and isoprene-derived nitrooxyorganosulfate detected at m/z 260 (isoprene NOS). Each aerosol filter sample was extracted in methanol; the extract was concentrated under gentle stream of nitrogen; the concentrated extract was dissolved in an analytical solvent to obtain an analytical sample; and the analytical sample was analyzed by an LC/MS instrument (Sato et al., 2007). The seasonal change in the concentration of cis-pinic acid, formed from α-pinene oxidation, was peaked in spring and fall, whereas the seasonal change in the concentration of 3-MBTCA, formed from oxidation of pinonic acid, was peaked in summer. Very similar results were reported in a previous paper on the GC/MS analysis of the same samples (Müller et al., 2017). The seasonal change in the concentration of α-pinene dimer was similar to that of cis-pinic acid, suggesting that a major formation process of the detected dimers was the atmospheric oxidation of α-pinene. The seasonal changes in the concentrations of isoprene OS and isoprene NOS, which are derived from isoprene epoxydiol (IEPOX), were peaked at fall and summer, respectively. The seasonal change in the concentration of isoprene NOS agreed well with that of 2-methyltetrols, molecular markers of isoprene secondary organic aerosol. These results suggest that a major formation process of isoprene NOS is secondary organic aerosol formation from isoprene in the presence of air pollutants.



References

Sato, K., Hatakeyama, S., Imamura, T., Secondary organic aerosol formation during the photooxidation of toluene: NO x dependence of chemical composition, J. Phys. Chem. A 111, 9796-9808 (2007).

Müller, A., Miyazaki, Y., Tachibana, E., Kawamura, K., Hiura, T., Evidence of a reduction in cloud condensation nuclei activity of water-soluble aerosols caused by biogenic emissions in a cool-temperate forest, Sci. Rep., 7, 8452 (2017).