Effects of NOx on the molecular composition of secondary organic aerosol formed by the ozonolysis and photooxidation of α-pinene. (October 2017)

• Record Type: Journal Article
• Authors: Park, Jun-Hyun; Babar, Zaeem Bin; Baek, Sun Jong; Kim, Hyun Sik; Lim, Ho-Jin
• Is Part Of: Atmospheric environment. Volume 166(2017)
• Page Start: 263
• Page End: 275
• Publication Date: 2017-10
• Subjects: Secondary organic aerosol -- α-Pinene -- NOx effect -- Molecular composition -- Fourier transform ion cyclotron resonance mass spectrometry; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2017.07.022
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: The molecular composition of secondary organic aerosol (SOA), obtained from the ozonolysis and photooxidation of α-pinene, was investigated using ultrahigh-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) in negative ion mode electrospray ionization (ESI). SOA formation was performed in an indoor smog chamber. The molecular formulae of individual species were identified on the basis of the measured ionic mass using guidelines, such as number of atoms, elemental ratios, and the nitrogen rule. In each of the SOAs obtained, 815–3501 monomeric and oligomeric (mainly dimeric) species were identified below m/z 800. From ozonolysis, mainly 95% of the typical oxygenated species (CHO) were detected, whereas from photooxidation under high NOx conditions, 32% of nitrogen-containing species (CHON) were detected. Several common intense species (e.g., C9 H14 O6, C10 H14 O6, C10 H16 O5, C17 H26 O7, C19 H28 O9, C10 H15 NO8, and C10 H15 NO9 ) could be listed as candidate tracers for the conventional tracers for α-pinene SOA. The increased percentage of CHON as a primary effect of NOx on the SOA composition evidently affected other physicochemical parameters, such as elemental ratios (i.e., O/C, H/C, and N/C), the double-bond equivalent (DBE), the carbon oxidation state (OSC ), and the organic-mass-to-carbon ratio (OM/OC). The O/C and OM/OC for CHON were greater than those observed for CHO, indicating that nitrogen preferentially exists in the oxidized form (e.g., -ONO2 ). The complexity of oligomerization was observed in DBE and OM/OC according to the number of carbon atoms. Graphical abstract: Highlights: The detailed molecular composition of SOA was identified by ultra-high resolution mass spectrometry. N-containing species were largely found in SOA formed under high NOx photooxidation. N-containing species were present in high O/C ratios with elevated carbon oxidation states. Several common abundant species demonstrate potential to be tracers for α-pinene SOA.