scholarly journals Analysis of functional groups in atmospheric aerosols by infrared spectroscopy: method development for probabilistic modeling of organic carbon and organic matter concentrations

2020 ◽  
Vol 13 (3) ◽  
pp. 1517-1538
Author(s):  
Charlotte Bürki ◽  
Matteo Reggente ◽  
Ann M. Dillner ◽  
Jenny L. Hand ◽  
Stephanie L. Shaw ◽  
...  
Keyword(s):  
Cluster Analysis ◽  
Organic Matter ◽  
Organic Carbon ◽  
Functional Groups ◽  
Method Development ◽  
Estimation Method ◽  
Chemical Species ◽  
Monitoring Network ◽  
Ftir Spectra ◽  
Absorption Bands

Abstract. The Fourier transform infrared (FTIR) spectra of fine particulate matter (PM2.5) contain many important absorption bands relevant for characterizing organic matter (OM) and obtaining organic matter to organic carbon (OM∕OC) ratios. However, extracting this information quantitatively – accounting for overlapping absorption bands and relating absorption to molar abundance – and furthermore relating abundances of functional groups to that of carbon atoms poses several challenges. In this work, we define a set of parameters that model these relationships and apply a probabilistic framework to identify values consistent with collocated field measurements of thermal–optical reflectance organic carbon (TOR OC). Parameter values are characterized for various sample types identified by cluster analysis of sample FTIR spectra, which are available for 17 sites in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network (7 sites in 2011 and 10 additional sites in 2013). The cluster analysis appears to separate samples according to predominant influence by dust, residential wood burning, wildfire, urban sources, and biogenic aerosols. Functional groups calibrations of aliphatic CH, alcohol COH, carboxylic acid COOH, carboxylate COO, and amine NH2 combined together reproduce TOR OC concentrations with reasonable agreement (r=0.96 for 2474 samples) and provide OM∕OC values generally consistent with our current best estimate of ambient OC. The mean OM∕OC ratios corresponding to sample types determined from cluster analysis range between 1.4 and 2.0, though ratios for individual samples exhibit a larger range. Trends in OM∕OC for sites aggregated by region or year are compared with another regression approach for estimating OM∕OC ratios from a mass closure equation of the major chemical species contributing to PM fine mass. Differences in OM∕OC estimates are observed according to estimation method and are explained through the sample types determined from spectral profiles of the PM.

scholarly journals Analysis of functional groups in atmospheric aerosols by infrared spectroscopy: method development for probabilistic modeling of organic carbon and organic matter concentrations

2019 ◽  
Author(s):  
Charlotte Bürki ◽  
Matteo Reggente ◽  
Ann M. Dillner ◽  
Jenny L. Hand ◽  
Stephanie L. Shaw ◽  
...  
Keyword(s):  
Cluster Analysis ◽  
Organic Matter ◽  
Organic Carbon ◽  
Method Development ◽  
Estimation Method ◽  
Ftir Spectra ◽  
Model Parameters ◽  
Probabilistic Framework ◽  
Absorption Bands ◽  
Homogeneous Groups

Abstract. The Fourier transform infrared (FTIR) spectra of fine particulate matter (PM2.5) contain many important absorption bands relevant for characterizing organic matter (OM) and obtaining organic matter to organic carbon (OM/OC) ratios. However, extracting this information quantitatively – accounting for overlapping absorption bands and relating absorption to molar abundance – poses several challenges. For instance, a subset of model parameters lead to calibrations that test almost indistinguishably well against laboratory standards generate substantially different predictions in ambient samples. Furthermore, additional parameters related to molecular structure are required to estimate carbon content from functional group (FG) abundance. However, since many carbon atoms can be branched (not fully functionalized) or polyfunctional, these parameters are not well constrained for ambient sample mixtures. In this work, we present a probabilistic framework to characterize combinations of these parameters that are consistent with field measurements of organic carbon (OC), for which estimates from thermal optical reflectance (TOR) measurements are used. Uncertainties in this probabilistic framework characterize the plausibility of many different parameter values that yield acceptable predictions (to the extent that they can be evaluated) neglected in conventional estimates of statistical uncertainties. Based on calibrations of aliphatic CH, alcohol COH, carboxylic acid COO, carboxylate COO, and amine NH2, we find model parameters for approximately homogeneous groups of samples determined from cluster analysis of FTIR spectra available for 17 sites in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network (7 sites in 2011 and 10 additional sites in 2013). These groups are interpreted as being predominantly influenced by dust, residential wood burning, wildfire, urban sources, and biogenic aerosols. The resulting calibrations reproduce TOR OC concentrations (R2 = 0.96) and provide OM/OC values consistent with our current best estimate of ambient OC. The mean OM/OC ratios corresponding to sample types determined from cluster analysis range between 1.4 and 2.0, though ratios for individual samples exhibit a larger range. Trends in OM/OC for sites aggregated by region or year are compared with another regression approach for estimating OM/OC ratios from a mass balance of the major chemical species contributing to PM fine mass. Differences in OM/OC estimates are observed according to estimation method and are explained through the sample types determined from spectral profiles of the PM.

scholarly journals Belowground allocation and dynamics of recently fixed plant carbon in a California annual grassland soil

2021 ◽  
Author(s):  
Christina Fossum ◽  
Katerina Estera-Molina ◽  
Mengting Yuan ◽  
Don Herman ◽  
Ilexis Chu-Jacoby ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Functional Groups ◽  
Heavy Fraction ◽  
Light Fraction ◽  
Pulse Field ◽  
Annual Grassland ◽  
Plant Shoots ◽  
California Annual Grassland ◽  
C Nmr

Plant roots and the organisms that surround them are a primary source for stabilized organic C, particularly in grassland soils, which have a large capacity to store organic carbon belowground. To quantify the flow and fate of plant fixed carbon (C) in a Northern California annual grassland, we tracked plant carbon from a five-day 13CO2 pulse field labeling for the following two years. Soil and plant samples were collected immediately after the pulse labeling, and again at three days, four weeks, six months, one year, and two years. Soil organic matter was fractionated using a sodium polytungstate density gradient to separate the free-light fraction (FLF), occluded-light fraction (OLF), and heavy fraction (HF). Using isotope ratio mass spectrometry, we measured 13C enrichment and total C content for plant shoots, roots, soil, soil dissolved organic carbon (DOC), and the FLF, OLF, and HF. The HF was further analyzed by solid state 13C NMR spectroscopy. At the end of the labeling period, the largest amount of 13C was recovered in plant shoots (60%), but a substantial amount (40%) was already found belowground in roots, soil, and soil DOC. Density fractionation of 4-week soil samples (from which living roots were removed) indicated that the highest isotope enrichment was in the mineral-rich heavy fraction, with similar enrichment of the FLF and OLF. At the 6-month sampling, after the dry summer period during which plants senesced and died, the amount of label in the FLF increased such that it was equal to that in the HF. By the 1-year sampling, 13C in the FLF had declined substantially and continued to decline by the 2-year sampling. 13C recovery in the OLF and HF, however, was qualitatively stable between sampling times. By the end of the 2-year experiment, 69% of remaining label was in the HF, 18% in the FLF and 13% in the OLF. While the total 13C content of the HF did not change significantly from the 4-week to the 2-year sample time, 13C NMR spectroscopic analysis of spring HF samples from 2018, 2019, and 2020 suggests that the relative proportion of aliphatic/alkyl functional groups declined in the newly formed SOC over the 2-year period. Simultaneously, aromatic and carbonyl functional groups increased, and the proportion of carbohydrate groups remained relatively constant. In summary, our results indicate that initial associations between minerals and root-derived organic matter are significant and form rapidly; by 4 weeks, a substantial amount (17%) of the total plant-derived 13C had become associated with the heavy fraction (HF) of soil. While the majority of annual C input cycles rapidly (<2-year timescale), a sizeable proportion (~12% of the original inputs) persisted for 2 years.

scholarly journals Identification of humic-like substances (HULIS) in oxygenated organic aerosols using NMR and AMS factor analyses and liquid chromatographic techniques

2014 ◽  
Vol 14 (1) ◽  
pp. 25-45 ◽  
Author(s):  
M. Paglione ◽  
A. Kiendler-Scharr ◽  
A. A. Mensah ◽  
E. Finessi ◽  
L. Giulianelli ◽  
...  
Keyword(s):  
Factor Analysis ◽  
Organic Carbon ◽  
Ion Exchange ◽  
Functional Groups ◽  
Organic Aerosols ◽  
Chemical Species ◽  
Water Soluble ◽  
Proton Nuclear Magnetic Resonance ◽  
Data Series ◽  
Aerosol Composition

Abstract. The atmospheric organic aerosol composition is characterized by a great diversity of functional groups and chemical species, challenging simple classification schemes. Traditional offline chemical methods identify chemical classes based on the retention behaviour on chromatographic columns and absorbing beds. Such an approach led to the isolation of complex mixtures of compounds such as the humic-like substances (HULIS). More recently, online aerosol mass spectrometry (AMS) was employed to identify chemical classes by extracting fragmentation patterns from experimental data series using statistical methods (factor analysis), providing simplified schemes for the classification of oxygenated organic aerosols (OOAs) on the basis of the distribution of oxygen-containing functionalities. The analysis of numerous AMS data sets suggested the occurrence of very oxidized OOAs which were postulated to correspond to HULIS. However, only a few efforts were made to test the correspondence of the AMS classes of OOAs with the traditional classifications from the offline methods. In this paper, we consider a case study representative of polluted continental regional background environments. We examine the AMS factors for OOAs identified by positive matrix factorization (PMF) and compare them to chemical classes of water-soluble organic carbon (WSOC) analysed offline on a set of filters collected in parallel. WSOC fractionation was performed by means of factor analysis applied to proton nuclear magnetic resonance (NMR) spectroscopic data, and by applying an ion-exchange chromatographic method for direct quantification of HULIS. Results show that the very oxidized low-volatility OOAs from AMS correlate with the NMR factor showing HULIS features and also with true "chromatographic" HULIS. On the other hand, UV/VIS-absorbing polyacids (or HULIS {sensu stricto}) isolated on ion-exchange beds were only a fraction of the AMS and NMR organic carbon fractions showing functional groups attributable to highly substituted carboxylic acids, suggesting that unspeciated low-molecular weight organic acids contribute to HULIS in the broad sense.

scholarly journals Towards Organic Carbon Isotope Records from Stalagmites: Coupled δ13C and 14C Analysis Using Wet Chemical Oxidation

Radiocarbon ◽  
2019 ◽  
Vol 61 (03) ◽  
pp. 749-764
Author(s):  
Franziska A Lechleitner ◽  
Susan Q Lang ◽  
Negar Haghipour ◽  
Cameron McIntyre ◽  
James U L Baldini ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Carbon Isotope ◽  
Method Development ◽  
Chemical Oxidation ◽  
Low Concentrations ◽  
Crucial Information ◽  
Isotopic Characterization ◽  
Wet Chemical

AbstractSpeleothem organic matter can be a powerful tracer for past environmental conditions and karst processes. Carbon isotope measurements (δ13C and 14C) in particular can provide crucial information on the provenance and age of speleothem organic matter, but are challenging due to low concentrations of organic matter in stalagmites. Here, we present a method development study on extraction and isotopic characterization of speleothem organic matter using a rapid procedure with low laboratory contamination risk. An extensive blank assessment allowed us to quantify possible sources of contamination through the entire method. Although blank contamination is consistently low (1.7 ± 0.34 – 4.3 ± 0.86 μg C for the entire procedure), incomplete sample decarbonation poses a still unresolved problem of the method, but can be detected when considering both δ13C and 14C values. We test the method on five stalagmites, showing reproducible results on samples as small as 7 μg C for δ13C and 20 μg C for 14C. Furthermore, we find consistently lower non-purgeable organic carbon (NPOC) 14C values compared to the carbonate 14C over the bomb spike interval in two stalagmites from Yok Balum Cave, Belize, suggesting overprint of a pre-aged or even fossil source of carbon on the organic fraction incorporated by these stalagmites.

scholarly journals Seasonal and spatial variability of the organic matter-to-organic carbon mass ratios in Chinese urban organic aerosols and a first report of high correlations between aerosol oxalic acid and zinc

2013 ◽  
Vol 13 (1) ◽  
pp. 1247-1277 ◽  
Author(s):  
L. Xing ◽  
T.-M. Fu ◽  
J. J. Cao ◽  
S. C. Lee ◽  
G. H. Wang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Oxalic Acid ◽  
Spatial Variability ◽  
Southern China ◽  
Chemical Species ◽  
Dicarboxylic Acids ◽  
Mass Ratio ◽  
Mass Ratios ◽  
Carbon Mass

Abstract. We calculated the organic matter to organic carbon mass ratios (OM/OC mass ratios) in PM2.5 collected from 14 Chinese cities during summer and winter of 2003 and analyzed the causes for their seasonal and spatial variability. The OM/OC mass ratios were calculated two ways. Using a mass balance method, the calculated OM/OC mass ratios averaged 1.92 ± 0.39 yr-round, with no significant seasonal or spatial variation. The second calculation was based on chemical species analyses of the organic compounds extracted from the PM2.5 samples using dichloromethane/methanol and water. The calculated OM/OC mass ratio in summer was relatively high (1.75 ± 0.13) and spatially-invariant, due to vigorous photochemistry and secondary OA production throughout the country. The calculated OM/OC mass ratio in winter (1.59 ± 0.18) was significantly lower than that in summer, with lower values in northern cities (1.51 ± 0.07) than in southern cities (1.65 ± 0.15). This likely reflects the wider usage of coal for heating purposes in northern China in winter, in contrast to the larger contributions from biofuel and biomass burning in southern China in winter. On average, organic matters constituted 36% and 34% of Chinese urban PM2.5 mass in summer and winter, respectively. We reported, for the first time, high correlations between Zn and oxalic acid in Chinese urban aerosols in summer. This is consistent with the formation of stable Zn oxalate complex in the aerosol phase previously proposed by Furukawa and Takahashi (2011). We found that many other dicarboxylic acids were also highly correlated with Zn in the summer Chinese urban aerosol samples, suggesting that they may also form stable organic complexes with Zn. Such formation may have profound implications for the atmospheric abundance and hygroscopic property of aerosol dicarboxylic acids.

scholarly journals Response of the chemical structure of soil organic carbon to modes of maize straw return

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shuqing Zheng ◽  
Jiuming Zhang ◽  
Fengqin Chi ◽  
Baoku Zhou ◽  
Dan Wei ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Functional Groups ◽  
Chemical Structure ◽  
Plant Residues ◽  
Straw Mulching ◽  
Soil Microbial ◽  
Straw Return ◽  
And Function

AbstractElucidating the chemical structure of soil organic matter (SOM) is important for accurately evaluating the stability and function of SOM. Aboveground vegetation directly affects the quantity and quality of exogenous organic matter input into the soil through plant residues and root exudates, which in turn affects soil microbial species, community structure, and activity, and ultimately impacts the chemical structure of SOM. In this study, a 13C nuclear magnetic resonance technique was used to analyze the chemical structure characteristics of soil organic carbon (SOC) under various rates of straw returning combined with rotary tillage and under full straw mulching. The results showed that full straw returning with rotary tillage and full straw mulching more effectively increased the SOC content than reduced rate of straw returning (1/2 and 1/3 of full straw) with rotary tillage. The contents of alkyl C and alkoxy C in the functional groups of SOC under various straw returning treatments were increased compared with those under the treatment of maize stubble remaining in soil (CK). Furthermore, the contents of aromatic C and carboxyl C were decreased, which were consistent with the chemical shift changes of SOC. Compared with CK treatment, straw returning decreased the content of aromatic C in the functional groups of SOC, but increased the content of alkoxy C, which could be associated with the change in integral areas of absorption peaks of alkyl C and alkoxy C moving toward left and right, respectively. The content of total SOC was significantly positively (P < 0.05) correlated with that of alkoxy C and significantly negatively (P < 0.01) correlated with that of aromatic C. The molecular structure of SOC tends to be simplified due to the decreasing in refractory C and the increasing in easily decomposed C after straw returning to the field.

Solution-state NMR investigation of the sorptive fractionation of dissolved organic matter by alkaline mineral soils

2013 ◽  
Vol 10 (4) ◽  
pp. 333 ◽  
Author(s):  
Perry J. Mitchell ◽  
André J. Simpson ◽  
Ronald Soong ◽  
Adi Oren ◽  
Benny Chefetz ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Functional Groups ◽  
Two Dimensional ◽  
Alkaline Soils ◽  
Dimensional Solution ◽  
Solution State ◽  
Before And After ◽  
Mineral Soils

Environmental context Dissolved organic matter plays a key role in global carbon cycling and environmental contaminant transport. We use one- and two-dimensional solution-state nuclear magnetic resonance spectroscopy to characterise dissolved organic matter before and after binding to alkaline subsoils with low organic carbon content. The results show that the dissolved organic matter is selectively fractionated through preferential binding of specific organic carbon functional groups. Abstract Sorption to clay minerals is a prominent fate of dissolved organic matter (DOM) in terrestrial environments. Previous studies have observed that DOM is selectively fractionated by interactions with both pure clay minerals and acidic mineral soils. However, the specific DOM functional groups that preferentially sorb to mineral surfaces in alkaline soils require further examination because higher basicity could change the nature of these sorptive interactions. Biosolids-derived DOM was characterised using one- and two-dimensional solution-state NMR spectroscopy before and after sorption to three alkaline subsurface mineral soils with varying mineralogy. Carboxylic DOM components sorbed preferentially to all soils, likely due to cation bridging and ligand exchange mechanisms. Aliphatic constituents were selectively retained only by a soil with high clay mineral content, possibly by van der Waals interactions with montmorillonite surfaces. Polar carbohydrate and peptide components of the DOM did not exhibit preferential sorption and may remain mobile in the soil solution and potentially stimulate microbial activity. A relatively low signal from aromatic DOM components prevented a full assessment of their sorption behaviour. The results suggest that DOM is selectively fractionated by similar interactions in both acidic and alkaline soils that may play a key role in the chemical and biochemical processes of subsurface environments.

scholarly journals Identification of humic-like substances (HULIS) in oxygenated organic aerosols using NMR and AMS factor analyses and liquid chromatographic techniques

2013 ◽  
Vol 13 (6) ◽  
pp. 17197-17252 ◽  
Author(s):  
M. Paglione ◽  
A. Kiendler-Scharr ◽  
A. A. Mensah ◽  
E. Finessi ◽  
L. Giulianelli ◽  
...  
Keyword(s):  
Factor Analysis ◽  
Organic Carbon ◽  
Ion Exchange ◽  
Functional Groups ◽  
Organic Aerosols ◽  
Chemical Species ◽  
Sensu Stricto ◽  
Water Soluble ◽  
Data Series ◽  
Aerosol Composition

Abstract. The atmospheric organic aerosol composition is characterized by a great diversity of functional groups and chemical species challenging simple classification schemes. Traditional off-line chemical methods identified chemical classes based on the retention behavior on chromatographic columns and absorbing beds. Such approach led to the isolation of complex mixtures of compounds such as the humic-like substances (HULIS). More recently, on-line aerosol mass spectrometry (AMS) was employed to identify chemical classes by extracting fragmentation patterns from experimental data series using statistical methods (factor analysis), providing simplified schemes for oxygenated organic aerosols (OOAs) classification on the basis of the distribution of oxygen-containing functionalities. The analysis of numerous AMS datasets suggested the occurrence of very oxidized OOAs which were postulated to correspond to the HULIS. However, only a few efforts were made to test the correspondence of the AMS classes of OOAs with the traditional classification from the off-line methods. In this paper, we consider a case study representative for polluted continental regional background environments. We examine the AMS factors for OOAs identified by positive matrix factorization (PMF) and compare to chemical classes of water-soluble organic carbon (WSOC) analysed off-line on a set of filters collected in parallel. WSOC fractionation was performed by means of factor analysis applied to H-NMR spectroscopic data, and by applying an ion-exchange chromatographic method for direct quantification of HULIS. Results show that the very oxidized low-volatility OOAs from AMS correlate with the NMR factor showing HULIS features and also with true "chromatographic" HULIS. On the other hand, UV/VIS-absorbing polyacids (or HULIS sensu stricto) isolated on ion-exchange beds were only a fraction of the AMS and NMR organic carbon fractions showing functional groups attributable to highly substituted carboxylic acids, suggesting that unspeciated low-molecular weight organic acids contribute to HULIS in the broad sense.

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