Nana Suto’s research while affiliated with Japan Automobile Research institute and other places

Ammonia gas (NH3) is an important alkaline air pollutant and a precursor to particulate matter, and its source has been thought to be agricultural, but in recent years, nonagricultural sources have been suspected. In this study, stable nitrogen isotope ratios of ammonium (δ15N-NH4+) in fine particulate matter (PM2.5) were measured at a suburban site and a rural site in Japan. Then, the long-term sources of NH4+ were identified using the δ15N-NH3 and an isotopic mixing model. The results showed that the averaged contribution from nonagricultural sources was 67% at the suburban site and 78% at the rural site. We also reanalyzed NH3 data collected at the same location. The result showed that the averaged contribution of nonagricultural sources to NH3 was 39%. This result is reasonable because bottom-up estimates are close to the contribution, and the NH3 emissions are affected by warm season activities in the rural site. It was first found that the sources vary greatly, depending on the gas and particles. Back-trajectory results suggested that PM2.5 measured at the rural site was derived from the Asian continent. We inferred that the NH4+ had been formed on the continent and that these particles thus represent transboundary pollution.

The sources and seasonal trends of water-soluble organic carbon (WSOC) in carbonaceous aerosols are of significant interest. From July 2017 to July 2019, we collected samples of PM2.5 (particulate matter, aerodynamic diameter<2.5µm) from one suburban and one rural site in Japan. The average δ13CWSOC was -25.2±1.1 ‰ and -24.6±2.4 ‰ at the suburban site and rural site, respectively. At the suburban site, the δ13CWSOC was consistent with the δ13C of burned C3 plants, and a high correlation was found between WSOC concentrations and non-sea-salt potassium concentrations; these results suggest that the main source of WSOC at this site was biomass burning of rice straw. At the rural site, the average δ13CWSOC was significantly heavier from autumn to spring (-23.9±2.1 ‰) than in summer (-27.4±0.7 ‰) (p<0.01). The δ13CWSOC from autumn to spring was consistent with that of biomass burning of rice straw, whereas that in summer was considered to reflect mainly the formation of secondary organic aerosols from biogenic volatile organic compounds (VOCs). The heaviest δ13CWSOC (-21.3±1.9 ‰) was observed from February to April 2019, which may be explained by long-range transport of C4 plant burning such as corn from overseas. Thus, the present study indicates that δ13CWSOC is potentially useful for elucidating the sources and atmospheric processes that contribute to seasonal variations of WSOC concentration.

Rationale There has never been a highly sensitive method for simultaneously measuring the δ¹⁵N and δ¹⁸O values of nitrate ions (NO3⁻) and the δ¹⁵N values of ammonium ions (NH4⁺) in particulate matter using denitrifying bacteria. In this study, we explored a method that combines use of an anion exchange resin and denitrifying bacteria to make such measurements. Methods The δ¹⁵N‐NH4⁺ values of samples obtained by the hypobromite and denitrifying bacteria method were measured by isotope ratio mass spectrometry. Tests (effect of flow rate, breakthrough, and acid concentration) were conducted to verify the removal of NO3⁻ using an AG1‐X8 anion exchange resin for NH4⁺ measurements and the enrichment of NO3⁻. For aerosol samples, the optimized method was used to measure the δ¹⁵N‐NO3⁻, δ¹⁸O‐NO3⁻, and δ¹⁵N‐NH4⁺ values of atmospheric particulate matter (PM2.5, aerodynamic diameter < 2.5 μm). Results The δ¹⁵N‐NO3⁻ and δ¹⁸O‐NO3⁻ values measured following extraction with 1–6 mol/L HCl, at sample flow rates of 1–2 mL/min, with total anion amounts of less than 2.2 mmol, and in concentration tests were found to be in very close agreement with reagent values. The precisions and the accuracies of the δ¹⁵N‐NH4⁺ and δ¹⁵N‐NO3⁻ values were in all cases less than 1‰. In addition, the accuracies for the δ¹⁸O‐NO3⁻ values were less than 1.4‰ and generally acceptable. The δ¹⁵N‐NH4⁺, δ¹⁵N‐NO3⁻, and δ¹⁸O‐NO3⁻ values in six PM2.5 samples were similar to those reported in previous studies. Conclusions Our proposed method for removing anions using the AG1‐X8 resin, for isotopic analysis using denitrifying bacteria, and for concentrating samples containing low concentrations of NO3⁻ will make it possible to perform high‐precision and accurate analyses easily and inexpensively. These methods are applicable not only to aerosols but also to samples from diverse locations such as rivers, the ocean, and Antarctica.

The sources and seasonal trends of water-soluble organic carbon (WSOC) in carbonaceous aerosols are of significant interest. From July 2017 to July 2019, we collected samples of PM2.5 (particulate matter, aerodynamic diameter

Liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) is used to analyze various types of samples, including foodstuffs, to determine their authenticity and trace their origin on the basis of their stable carbon isotope ratios (δ13C). However, multicomponent samples are difficult to analyze. For example, determining the δ13C values of the organic acids in honey is complicated by the presence of large amounts of carbohydrates. Herein, we present a heart-cutting two-dimensional LC/IRMS method for analysis of honey samples. In this method, the organic acids in the samples were first separated from the carbohydrates by a size-exclusion column, and then the organic acids were separated from each other by a reverse-phase column connected to the first column via a switching valve. By means of this method, the δ13C values for three organic acids in high-carbohydrate-content simulated honey samples could be determined with high accuracy and precision (≤0.3‰ and ≤0.1‰, respectively). In addition, the gluconic acid δ13C values for 25 honey samples were determined with high precision and found to range from -31.7 to -28.5‰ (mean: -30.0 ± 0.7‰). These values shed some light on the mechanism of gluconic acid production. Taken together, our results suggest that this two-dimensional LC method has the potential to be more effective than one-dimensional LC for use in isotopic research.

Stable carbon isotope ratios (δ ¹³ C) for glucose, fructose, disaccharides, trisaccharides, and organic acids in 116 commercial honey samples were measured by LC/IRMS. On the basis of EA/IRMS and LC/IRMS authenticity criteria, 39 of the samples were judged to have been adulterated. The δ ¹³ C values for organic acids from pure honey, reported here for the first time, ranged from −33.6 to −26.5‰. The mean Δδ ¹³ C (glucose–organic acids) value was +3.7 ± 0.9‰. Glucose and organic acid δ ¹³ C values were strongly correlated (R = 0.71, P < 0.001). Gluconic acid, the predominant organic acid in honey, has been reported to be produced via decomposition of glucose by bee glucose-oxidase and certain Gluconobacter spp. This fact was confirmed by isotope analysis.

The cover image, by Nana Suto and Hiroto Kawashima, is based on the Research Article Online wet oxidation/isotope ratio mass spectrometry method for determination of stable carbon isotope ratios of water‐soluble organic carbon in particulate matter, https://doi.org/10.1002/rcm.8240.

Rationale Water‐soluble organic carbon (WSOC) is formed by oxidation of organic compounds in particulate matter (PM) and accounts for 25–80% of the organic carbon in PM. Stable carbon isotope ratio (δ¹³C) analysis is widely used to identify the sources of PM, but determining the δ¹³C values of WSOC is complicated and requires a time‐consuming pretreatment process. Methods We have developed an online wet oxidation/isotope ratio mass spectrometry method with a reduced pretreatment time. We have measured the δ¹³C values of WSOC by using this method. Results The method showed high accuracy (0.1‰) and precision (0.1‰) for levoglucosan, and the limit of detection was sufficiently low for WSOC analysis. Using this method, we determined δ¹³C values of WSOC in PM2.5 samples collected in Japan during the period from July to November and found that the values ranged from −26.5‰ to −25.0‰ (average, −25.8‰). Conclusions Our simple, low‐blank method could be used for rapid quantitative analysis of the δ¹³C values of WSOC in PM2.5. We propose that this online method be used as a standard method for δ¹³C analysis of WSOC.

Rationale Liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) has been used to authenticate and trace products such as honey, wine, and lemon juice, and compounds such as caffeine and pesticides. However, LC/IRMS has several disadvantages, including the high cost of the CO2 membrane and blocking by solidified sodium persulfate. Here, we developed an improved system for determining carbon isotope ratios by LC/IRMS. Methods The main improvement was the use of a post‐column pump. Using the improved system, we determined δ¹³C values for glucose with high accuracy and precision (0.1‰ and 0.1‰, respectively; n = 3). The glucose, fructose, disaccharide, trisaccharide, and organic acid constituents of the honey samples were analyzed by LC/IRMS. Results The δ¹³C values for glucose, fructose, disaccharides, trisaccharides, and organic acids ranged from –27.0 to –24.2‰, –26.8 to –24.0‰, –28.8 to –24.0‰, –27.8 to –22.8‰, and –30.6 to –27.4‰, respectively. The analysis time was 1/3–1/2 the times required for analysis by previously reported methods. Conclusions The column flow rate could be arbitrarily adjusted with the post‐column pump. We applied the improved method to 26 commercial honey samples. Our results can be expected to be useful for other researchers who use LC/IRMS.

The compound specific isotope analysis is nowadays an important and powerful tool in geochemical, environmental and forensics field. On November 2013, Aqli Foods Corporation in Japan dealt with complaints about stench from frozen foods produced. Subsequently, very high concentrations of organophosphorus pesticide as malathion, ethylbenzene and xylene were detected in recovered frozen foods. In particular case, we present the method to measure the stable carbon isotope ratio (δ¹³C) of nine malathion emulsion pesticides using gas chromatography/isotope ratio mass spectrometry (GC/IRMS) to identify the source. The δ¹³C values of malathion ranged from − 30.6‰ to − 29.5‰. Because malathion used in all malathion emulsions sold in Japan is imported from the same overseas company, Cheminova, Denmark. The δ¹³C values of ethylbenzene ranged from − 28.2‰ to − 20.8‰ and those of m,p-xylene from − 28.7‰ to − 25.2‰. The differences in the δ¹³C values may be because of the material itself and chemical processing. We also determined the ratio of ethylbenzene to m,p-xylene and finally categorized the nine malathion samples into five groups on the basis of this ratio and the δ¹³C values of ethylbenzene and m,p-xylene. The results of isotopic fractionation during volatilization (refrigerate, room temperature and incubator) was negligible small.