Analysis of the Unresolved Organic Fraction in Atmospheric Aerosols with Ultrahigh-Resolution Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy: Organosulfates As Photochemical Smog Constituents

Abstract

Complementary molecular and atomic signatures obtained from Fourier transform ion cyclotron resonance (FTICR) mass spectra and NMR spectra provided unequivocal attribution of CHO, CHNO, CHOS, and CHNOS molecular series in secondary organic aerosols (SOA) and high-resolution definition of carbon chemical environments. Sulfate esters were confirmed as major players in SOA formation and as major constituents of its water-soluble fraction (WSOC). Elevated concentrations of SO(2), sulfate, and photochemical activity were shown to increase the proportion of SOA sulfur-containing compounds. Sulfonation of CHO precursors by means of heterogeneous reactions between carbonyl derivatives and sulfuric acid in gas-phase photoreactions was proposed as a likely formation mechanism of CHOS molecules. In addition, photochemistry induced oligomerization processes of CHOS molecules. Methylesters found in methanolic extracts of a SOA subjected to strong photochemical exposure were considered secondary products derived from sulfate esters by methanolysis. The relative abundance of nitrogen-containing compounds (CHNO and CHNOS series) appeared rather dependent on local effects such as biomass burning. Extensive aliphatic branching and disruption of extended NMR spin-systems by carbonyl derivatives and other heteroatoms were the most significant structural motifs in SOA. The presence of heteroatoms in elevated oxidation states suggests a clearly different SOA formation trajectory in comparison with established terrestrial and aqueous natural organic matter.

Physico-chemical characterization of SOA derived from catechol and guaiacol – a model substance for the aromatic fraction of atmospheric HULIS

“…11a) and is comparable to other SOA samples from photooxidation Schmitt-Kopplin et al, 2010). The distribution of the m/z signal in ICR-FT/MS is very similar between the catechol-and guaiacol-aerosol extracts.…”

“…Electrospray injection was followed in negative mode with an APOLLO II electrospray source in flow injection at 2 µl/min (Gaspar et al, 2009, andSchmitt-Kopplin et al, 2010). The molecular formulae were batch-calculated by a software tool, written in-house and achieving a maximum mass error of ≤0.2 ppm.…”

“…Furthermore, light-absorption of organic materials plays an important role for the radiative forcing (Shapiro et al, 2009). To complete and confirm spectroscopic results ultrahigh resolution mass spectroscopy (ICR-FT/MS, Schmitt-Kopplin et al, 2010) and imaging by electron microscopy are used in the present study.…”

Oligomer Formation Pathways in Secondary Organic Aerosol from MS and MS/MS Measurements with High Mass Accuracy and Resolving Power

“…Correlating measured oligomer elemental formulas with predicted formulas based on combinations of known monomers and intermediates has suggested that carboxylic acid groups [12], the stabilized Criegee intermediate [8], and hydroperoxide intermediates [8,12] may be important monomer building blocks. Recently, accurate mass analysis has been extended to tandem mass spectrometry (MS n ) experiments either by direct infusion [9,13] or coupled with liquid chromatography [14] to more fully characterize specific oligomer products of interest.…”

Aerosols and health: a challenge for chemical and biological analysis

“…Still a large fraction of the organic inventory of emission-and ambient-PM is unidentified [3]. As described in the review within this topical collection, several high-end analytical chemical approaches based on mass spectrometry, such as comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry [23] or ultra-high resolution mass spectrometry [21] can be used to address the yet unknown chemical space of aerosol PM. An important aspect for all mass spectrometric technologies, however, in this context is the ionization method used for the mass spectrometric detection.…”