Characterization of water-soluble organic matter in urban aerosol by 1H-NMR spectroscopy

Abstract

The functional and 13C isotopic compositions of water-soluble organic carbon (WSOC) in atmospheric aerosol were determined by nuclear magnetic resonance (1H-NMR) and isotope ratio mass spectrometry (IRMS) in an urban location in the Southern Mississippi Valley. The origin of WSOC was resolved using the functional distribution of organic hydrogen, δ13C ratio, and positive matrix factorization (PMF). Three factors were retained based on NMR spectral bins loadings. Two factors (factors 1 and 3) demonstrated strong associations with the aliphatic region in the NMR spectra and levoglucosan resonances. Differences between the two factors included the abundance of the aromatic functional group for factor 1, indicating fresh emissions and, for factor 3, the presence of resonances attributed to secondary ammonium nitrate and low δ13C ratio values that are indicative of secondary organic aerosol. Factors 1 and 3 added 0.89 and 1.08 μgC m−3, respectively, with the highest contribution in the summer and fall. Factor 2 retained resonances consistent with saccharides and was attributed to pollen particles. Its contribution to WSOC varied from 0.22 μgC m−3 in winter to 1.04 μgC m−3 in spring.

Structural signatures of water-soluble organic aerosols in contrasting environments in South America and Western Europe

“…3, regardless of the studied environment, all aerosol WSOC samples exhibit the same major proton types; however, they differ in terms of the relative distribution of the major proton regions. Overall, the relative content of the proton functional groups obtained in this study are within the range of those published for WSOC hydrophobic acid fractions or "humic-like substances (HULIS)" from atmospheric aerosols (e.g., Graham et al, 2002;Decesari et al, 2005;Song et al, 2012;Chalbot et al, 2014Chalbot et al, , 2016Lopes et al, 2015). For the South American sites, the saturated aliphatic protons are the most important component (36e59%), followed by unsaturated (20e33%) and oxygenated (13e40%) aliphatic protons, and a less contribution from aromatic protons (2.0e10%).…”

“…The presence of polyols and anhydrosugars associated with pollen and fresh smoke particles (with high HeCeO/SAliphatics (>0.4) but low HeCeC¼O/SAliphatics (<0.25) ratios) could contribute for the clear separation of these PM 10 samples from the remaining WSOC samples that are impacted by anthropogenic-related processes. Particularly, the aerosol WSOC samples collected in PV during IBB and MBB emissions are characterized by HeCeO/ SAliphatics and HeCeC¼O/SAliphatics ratios comparable to those computed for primary emissions from biomass burning (Chalbot et al, 2016) and pollen-dominated coarse particles (Chalbot et al, Fig. 4.…”

“…2) of the WSOC samples collected in PV -MBB, Medellín, Bogota, and Buenos Aires exhibit two distinct peaks at d 1 H 3.98 and 4.61 ppm, which are likely assigned to the protons in the H-O-groups of a sugar alcohol skeleton, thus supporting the contribution of fungal spores and pollen into the water-soluble OA composition at these locations. Nevertheless, H-C-O structures in PV e MBB and Bogota may also have a secondary origin, as a result of photochemical reactions (e.g., stronger solar radiation in Bogota, Table S1), and/or atmospheric aging of primary OA during warmer conditions (e.g., average temperature of 26 C in PV e MBB, Table S1) (Shakya et al, 2012;Chalbot et al, 2016). The strong H-C-O signature in the NMR spectra of samples from Medellín and Buenos Aires during winter and winter/spring seasons, could also be attributed to the presence of carbohydrate-like moieties likely derived from plant cellulose and hemicellulose pyrolysis, which underpins the contribution of biomass burning emissions to the urban OA.…”

“…The approach chosen to fulfill this objective encompasses functional group analysis using proton nuclear magnetic resonance ( 1 H NMR) spectroscopy. This strategy has been successfully applied to different aerosol WSOC samples, namely from biomass burning aerosols, marine organic aerosols, secondary organic aerosols (SOA), urban aerosols, rural aerosols, and size-fractionated atmospheric aerosols Tagliavini et al, 2006;Decesari et al, 2007;Chalbot et al, 2014Chalbot et al, , 2016Lopes et al, 2015). In this study, the acquired 1 H NMR datasets were further used to build fingerprints for source contribution analysis, following the method of Decesari et al (2007).…”

“…In the quest for untangle the complex molecular composition of the water-soluble component of OA, it has been shown that the WSOC consists of a highly diverse suite of oxygenated compounds, including dicarboxylic acids, keto-carboxylic acids, aliphatic aldehydes and alcohols, saccharides, saccharide anhydrides, aromatic acids, phenols, but also amines, amino acids, organic nitrates, and organic sulfates (e.g., Duarte et al, 2007Duarte et al, , 2008Duarte et al, , 2015Timonen et al, 2013;Ng et al, 2010;Cleveland et al, 2012;Shakya et al, 2012;Pietrogrande et al, 2013;Chalbot et al, 2014;Paglione et al, 2014;Lopes et al, 2015;Chalbot et al, 2016). A common ground of the available compositional datasets on aerosol WSOC is that they refer to studies carried out in urban, rural, and remote locations predominantly at North America and Europe, besides a few urban sites in Asia.…”